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* [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
@ 2022-04-04 21:39 Noah Goldstein
  2022-04-27 16:25 ` Noah Goldstein
                   ` (2 more replies)
  0 siblings, 3 replies; 10+ messages in thread
From: Noah Goldstein @ 2022-04-04 21:39 UTC (permalink / raw)
  To: libc-alpha

'get_fast_jitter' is meant to be used purely for performance
purposes. In all cases it's used it should be acceptable to get no
randomness (see default case). An example use case is in setting
jitter for retries between threads at a lock. There is a
performance benefit to having jitter, but only if the jitter can
be generated very quickly and ultimately there is no serious issue
if no jitter is generated.

The implementation generally uses 'HP_TIMING_NOW' or another cycle
counter when the architecture supports it. The default case just
returns zero.
---
 sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
 sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
 sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
 sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
 sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
 sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
 6 files changed, 198 insertions(+)
 create mode 100644 sysdeps/aarch64/fast-jitter.h
 create mode 100644 sysdeps/alpha/fast-jitter.h
 create mode 100644 sysdeps/generic/fast-jitter.h
 create mode 100644 sysdeps/s390/fast-jitter.h
 create mode 100644 sysdeps/sparc/fast-jitter.h
 create mode 100644 sysdeps/x86_64/fast-jitter.h

diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
new file mode 100644
index 0000000000..fb09d2632c
--- /dev/null
+++ b/sysdeps/aarch64/fast-jitter.h
@@ -0,0 +1,33 @@
+/* Fast jitter on arm with HP_TIMING_NOW
+   Copyright (C) 2022-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+#include <hp-timing.h>
+
+static inline uint32_t
+get_fast_jitter (void)
+{
+  hp_timing_t jitter;
+  HP_TIMING_NOW (jitter);
+  return (uint32_t) jitter;
+}
+
+#endif
diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
new file mode 100644
index 0000000000..0a24290eaa
--- /dev/null
+++ b/sysdeps/alpha/fast-jitter.h
@@ -0,0 +1,34 @@
+/* Fast jitter on alpha with rpcc
+   Copyright (C) 2022-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+
+static inline uint32_t
+get_fast_jitter (void)
+{
+  unsigned long int x_;
+  asm volatile ("rpcc %0" : "=r"(x_));
+  /* Don't both with process offset.  We only need jitter not
+     monotonic cycle count.  */
+  return (uint32_t) x;
+}
+
+#endif
diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
new file mode 100644
index 0000000000..63bcf3ccd7
--- /dev/null
+++ b/sysdeps/generic/fast-jitter.h
@@ -0,0 +1,35 @@
+/* Fallback for fast jitter just return 0.
+   Copyright (C) 2019-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+
+/* Baseline just return 0.  We could create jitter using a clock or
+   'random_bits' but that may imply a syscall and the goal of
+   'get_fast_jitter' is minimal overhead "randomness" when such
+   randomness helps performance.  Adding high overhead the function
+   defeats the purpose.  */
+static inline uint32_t
+get_fast_jitter (void)
+{
+  return 0;
+}
+
+#endif
diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
new file mode 100644
index 0000000000..eb905b1413
--- /dev/null
+++ b/sysdeps/s390/fast-jitter.h
@@ -0,0 +1,33 @@
+/* Fast jitter on s390 with HP_TIMING_NOW
+   Copyright (C) 2022-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+#include <hp-timing.h>
+
+static inline uint32_t
+get_fast_jitter (void)
+{
+  hp_timing_t jitter;
+  HP_TIMING_NOW (jitter);
+  return (uint32_t) jitter;
+}
+
+#endif
diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
new file mode 100644
index 0000000000..f4413754c5
--- /dev/null
+++ b/sysdeps/sparc/fast-jitter.h
@@ -0,0 +1,33 @@
+/* Fast jitter on sparc with HP_TIMING_NOW
+   Copyright (C) 2022-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+#include <hp-timing.h>
+
+static inline uint32_t
+get_fast_jitter (void)
+{
+  hp_timing_t jitter;
+  HP_TIMING_NOW (jitter);
+  return (uint32_t) jitter;
+}
+
+#endif
diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
new file mode 100644
index 0000000000..1140f1c295
--- /dev/null
+++ b/sysdeps/x86_64/fast-jitter.h
@@ -0,0 +1,30 @@
+/* X86 use rdtsc to quickly generate pseudo-random for jitter
+   Copyright (C) 2022-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+#include <stdint.h>
+
+static inline uint32_t
+get_fast_jitter (void)
+{
+  return __builtin_ia32_rdtsc ();
+}
+
+#endif
-- 
2.25.1


^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-04 21:39 [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h Noah Goldstein
@ 2022-04-27 16:25 ` Noah Goldstein
  2022-04-27 17:47 ` Adhemerval Zanella
  2022-04-27 20:13 ` [PATCH v2] " Noah Goldstein
  2 siblings, 0 replies; 10+ messages in thread
From: Noah Goldstein @ 2022-04-27 16:25 UTC (permalink / raw)
  To: GNU C Library

On Mon, Apr 4, 2022 at 4:39 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> 'get_fast_jitter' is meant to be used purely for performance
> purposes. In all cases it's used it should be acceptable to get no
> randomness (see default case). An example use case is in setting
> jitter for retries between threads at a lock. There is a
> performance benefit to having jitter, but only if the jitter can
> be generated very quickly and ultimately there is no serious issue
> if no jitter is generated.
>
> The implementation generally uses 'HP_TIMING_NOW' or another cycle
> counter when the architecture supports it. The default case just
> returns zero.
> ---
>  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
>  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
>  6 files changed, 198 insertions(+)
>  create mode 100644 sysdeps/aarch64/fast-jitter.h
>  create mode 100644 sysdeps/alpha/fast-jitter.h
>  create mode 100644 sysdeps/generic/fast-jitter.h
>  create mode 100644 sysdeps/s390/fast-jitter.h
>  create mode 100644 sysdeps/sparc/fast-jitter.h
>  create mode 100644 sysdeps/x86_64/fast-jitter.h
>
> diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> new file mode 100644
> index 0000000000..fb09d2632c
> --- /dev/null
> +++ b/sysdeps/aarch64/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on arm with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> new file mode 100644
> index 0000000000..0a24290eaa
> --- /dev/null
> +++ b/sysdeps/alpha/fast-jitter.h
> @@ -0,0 +1,34 @@
> +/* Fast jitter on alpha with rpcc
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  unsigned long int x_;
> +  asm volatile ("rpcc %0" : "=r"(x_));
> +  /* Don't both with process offset.  We only need jitter not
> +     monotonic cycle count.  */
> +  return (uint32_t) x;
> +}
> +
> +#endif
> diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> new file mode 100644
> index 0000000000..63bcf3ccd7
> --- /dev/null
> +++ b/sysdeps/generic/fast-jitter.h
> @@ -0,0 +1,35 @@
> +/* Fallback for fast jitter just return 0.
> +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +/* Baseline just return 0.  We could create jitter using a clock or
> +   'random_bits' but that may imply a syscall and the goal of
> +   'get_fast_jitter' is minimal overhead "randomness" when such
> +   randomness helps performance.  Adding high overhead the function
> +   defeats the purpose.  */
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return 0;
> +}
> +
> +#endif
> diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> new file mode 100644
> index 0000000000..eb905b1413
> --- /dev/null
> +++ b/sysdeps/s390/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on s390 with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> new file mode 100644
> index 0000000000..f4413754c5
> --- /dev/null
> +++ b/sysdeps/sparc/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on sparc with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> new file mode 100644
> index 0000000000..1140f1c295
> --- /dev/null
> +++ b/sysdeps/x86_64/fast-jitter.h
> @@ -0,0 +1,30 @@
> +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return __builtin_ia32_rdtsc ();
> +}
> +
> +#endif
> --
> 2.25.1
>

Ping.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-04 21:39 [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h Noah Goldstein
  2022-04-27 16:25 ` Noah Goldstein
@ 2022-04-27 17:47 ` Adhemerval Zanella
  2022-04-27 18:04   ` H.J. Lu
  2022-04-27 20:13 ` [PATCH v2] " Noah Goldstein
  2 siblings, 1 reply; 10+ messages in thread
From: Adhemerval Zanella @ 2022-04-27 17:47 UTC (permalink / raw)
  To: libc-alpha, Noah Goldstein



On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> 'get_fast_jitter' is meant to be used purely for performance
> purposes. In all cases it's used it should be acceptable to get no
> randomness (see default case). An example use case is in setting
> jitter for retries between threads at a lock. There is a
> performance benefit to having jitter, but only if the jitter can
> be generated very quickly and ultimately there is no serious issue
> if no jitter is generated.
> 
> The implementation generally uses 'HP_TIMING_NOW' or another cycle
> counter when the architecture supports it. The default case just
> returns zero.

I think it should ok, although I think it would be better to be sent
along with a actual usage (as the pthread mutex optimization).

> ---
>  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
>  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
>  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
>  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
>  6 files changed, 198 insertions(+)
>  create mode 100644 sysdeps/aarch64/fast-jitter.h
>  create mode 100644 sysdeps/alpha/fast-jitter.h
>  create mode 100644 sysdeps/generic/fast-jitter.h
>  create mode 100644 sysdeps/s390/fast-jitter.h
>  create mode 100644 sysdeps/sparc/fast-jitter.h
>  create mode 100644 sysdeps/x86_64/fast-jitter.h
> 
> diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> new file mode 100644
> index 0000000000..fb09d2632c
> --- /dev/null
> +++ b/sysdeps/aarch64/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on arm with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> new file mode 100644
> index 0000000000..0a24290eaa
> --- /dev/null
> +++ b/sysdeps/alpha/fast-jitter.h
> @@ -0,0 +1,34 @@
> +/* Fast jitter on alpha with rpcc
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  unsigned long int x_;
> +  asm volatile ("rpcc %0" : "=r"(x_));
> +  /* Don't both with process offset.  We only need jitter not
> +     monotonic cycle count.  */
> +  return (uint32_t) x;
> +}
> +
> +#endif
> diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> new file mode 100644
> index 0000000000..63bcf3ccd7
> --- /dev/null
> +++ b/sysdeps/generic/fast-jitter.h
> @@ -0,0 +1,35 @@
> +/* Fallback for fast jitter just return 0.
> +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +/* Baseline just return 0.  We could create jitter using a clock or
> +   'random_bits' but that may imply a syscall and the goal of
> +   'get_fast_jitter' is minimal overhead "randomness" when such
> +   randomness helps performance.  Adding high overhead the function
> +   defeats the purpose.  */
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return 0;
> +}
> +
> +#endif
> diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> new file mode 100644
> index 0000000000..eb905b1413
> --- /dev/null
> +++ b/sysdeps/s390/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on s390 with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> new file mode 100644
> index 0000000000..f4413754c5
> --- /dev/null
> +++ b/sysdeps/sparc/fast-jitter.h
> @@ -0,0 +1,33 @@
> +/* Fast jitter on sparc with HP_TIMING_NOW
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +#include <hp-timing.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +}
> +
> +#endif
> diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> new file mode 100644
> index 0000000000..1140f1c295
> --- /dev/null
> +++ b/sysdeps/x86_64/fast-jitter.h
> @@ -0,0 +1,30 @@
> +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +#include <stdint.h>
> +
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +  return __builtin_ia32_rdtsc ();

Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
only a generic implementation like:

static inline uint32_t
get_fast_jitter (void)
{
#if HP_TIMING_INLINE
  hp_timing_t jitter;
  HP_TIMING_NOW (jitter);
  return (uint32_t) jitter;
#else
  return 0;
#endif
}

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-27 17:47 ` Adhemerval Zanella
@ 2022-04-27 18:04   ` H.J. Lu
  2022-04-27 20:13     ` Noah Goldstein
  0 siblings, 1 reply; 10+ messages in thread
From: H.J. Lu @ 2022-04-27 18:04 UTC (permalink / raw)
  To: Adhemerval Zanella; +Cc: GNU C Library, Noah Goldstein

On Wed, Apr 27, 2022 at 10:48 AM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
>
> On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> > 'get_fast_jitter' is meant to be used purely for performance
> > purposes. In all cases it's used it should be acceptable to get no
> > randomness (see default case). An example use case is in setting
> > jitter for retries between threads at a lock. There is a
> > performance benefit to having jitter, but only if the jitter can
> > be generated very quickly and ultimately there is no serious issue
> > if no jitter is generated.
> >
> > The implementation generally uses 'HP_TIMING_NOW' or another cycle
> > counter when the architecture supports it. The default case just
> > returns zero.
>
> I think it should ok, although I think it would be better to be sent
> along with a actual usage (as the pthread mutex optimization).
>
> > ---
> >  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
> >  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
> >  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
> >  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
> >  6 files changed, 198 insertions(+)
> >  create mode 100644 sysdeps/aarch64/fast-jitter.h
> >  create mode 100644 sysdeps/alpha/fast-jitter.h
> >  create mode 100644 sysdeps/generic/fast-jitter.h
> >  create mode 100644 sysdeps/s390/fast-jitter.h
> >  create mode 100644 sysdeps/sparc/fast-jitter.h
> >  create mode 100644 sysdeps/x86_64/fast-jitter.h
> >
> > diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> > new file mode 100644
> > index 0000000000..fb09d2632c
> > --- /dev/null
> > +++ b/sysdeps/aarch64/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on arm with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> > new file mode 100644
> > index 0000000000..0a24290eaa
> > --- /dev/null
> > +++ b/sysdeps/alpha/fast-jitter.h
> > @@ -0,0 +1,34 @@
> > +/* Fast jitter on alpha with rpcc
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  unsigned long int x_;
> > +  asm volatile ("rpcc %0" : "=r"(x_));
> > +  /* Don't both with process offset.  We only need jitter not
> > +     monotonic cycle count.  */
> > +  return (uint32_t) x;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > new file mode 100644
> > index 0000000000..63bcf3ccd7
> > --- /dev/null
> > +++ b/sysdeps/generic/fast-jitter.h
> > @@ -0,0 +1,35 @@
> > +/* Fallback for fast jitter just return 0.
> > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +/* Baseline just return 0.  We could create jitter using a clock or
> > +   'random_bits' but that may imply a syscall and the goal of
> > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > +   randomness helps performance.  Adding high overhead the function
> > +   defeats the purpose.  */
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  return 0;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> > new file mode 100644
> > index 0000000000..eb905b1413
> > --- /dev/null
> > +++ b/sysdeps/s390/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on s390 with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> > new file mode 100644
> > index 0000000000..f4413754c5
> > --- /dev/null
> > +++ b/sysdeps/sparc/fast-jitter.h
> > @@ -0,0 +1,33 @@
> > +/* Fast jitter on sparc with HP_TIMING_NOW
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +#include <hp-timing.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +}
> > +
> > +#endif
> > diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> > new file mode 100644
> > index 0000000000..1140f1c295
> > --- /dev/null
> > +++ b/sysdeps/x86_64/fast-jitter.h
> > @@ -0,0 +1,30 @@
> > +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +#include <stdint.h>
> > +
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +  return __builtin_ia32_rdtsc ();
>
> Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
> only a generic implementation like:
>
> static inline uint32_t
> get_fast_jitter (void)
> {
> #if HP_TIMING_INLINE
>   hp_timing_t jitter;
>   HP_TIMING_NOW (jitter);
>   return (uint32_t) jitter;
> #else
>   return 0;
> #endif
> }

I'd like this version.  Noah, can you send v2?

Thanks,

-- 
H.J.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* [PATCH v2] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-04 21:39 [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h Noah Goldstein
  2022-04-27 16:25 ` Noah Goldstein
  2022-04-27 17:47 ` Adhemerval Zanella
@ 2022-04-27 20:13 ` Noah Goldstein
  2022-04-27 20:46   ` H.J. Lu
  2 siblings, 1 reply; 10+ messages in thread
From: Noah Goldstein @ 2022-04-27 20:13 UTC (permalink / raw)
  To: libc-alpha

'get_fast_jitter' is meant to be used purely for performance
purposes. In all cases it's used it should be acceptable to get no
randomness (see default case). An example use case is in setting
jitter for retries between threads at a lock. There is a
performance benefit to having jitter, but only if the jitter can
be generated very quickly and ultimately there is no serious issue
if no jitter is generated.

The implementation generally uses 'HP_TIMING_NOW' iff it is
inlined (avoid any potential syscall paths).
---
 sysdeps/generic/fast-jitter.h | 42 +++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 sysdeps/generic/fast-jitter.h

diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
new file mode 100644
index 0000000000..4dd53e3475
--- /dev/null
+++ b/sysdeps/generic/fast-jitter.h
@@ -0,0 +1,42 @@
+/* Fallback for fast jitter just return 0.
+   Copyright (C) 2019-2022 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _FAST_JITTER_H
+# define _FAST_JITTER_H
+
+# include <stdint.h>
+# include <hp-timing.h>
+
+/* Baseline just return 0.  We could create jitter using a clock or
+   'random_bits' but that may imply a syscall and the goal of
+   'get_fast_jitter' is minimal overhead "randomness" when such
+   randomness helps performance.  Adding high overhead the function
+   defeats the purpose.  */
+static inline uint32_t
+get_fast_jitter (void)
+{
+# if HP_TIMING_INLINE
+  hp_timing_t jitter;
+  HP_TIMING_NOW (jitter);
+  return (uint32_t) jitter;
+# else
+  return 0;
+# endif
+}
+
+#endif
-- 
2.25.1


^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-27 18:04   ` H.J. Lu
@ 2022-04-27 20:13     ` Noah Goldstein
  0 siblings, 0 replies; 10+ messages in thread
From: Noah Goldstein @ 2022-04-27 20:13 UTC (permalink / raw)
  To: H.J. Lu; +Cc: Adhemerval Zanella, GNU C Library

On Wed, Apr 27, 2022 at 1:05 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Wed, Apr 27, 2022 at 10:48 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> >
> >
> > On 04/04/2022 18:39, Noah Goldstein via Libc-alpha wrote:
> > > 'get_fast_jitter' is meant to be used purely for performance
> > > purposes. In all cases it's used it should be acceptable to get no
> > > randomness (see default case). An example use case is in setting
> > > jitter for retries between threads at a lock. There is a
> > > performance benefit to having jitter, but only if the jitter can
> > > be generated very quickly and ultimately there is no serious issue
> > > if no jitter is generated.
> > >
> > > The implementation generally uses 'HP_TIMING_NOW' or another cycle
> > > counter when the architecture supports it. The default case just
> > > returns zero.
> >
> > I think it should ok, although I think it would be better to be sent
> > along with a actual usage (as the pthread mutex optimization).


> >
> > > ---
> > >  sysdeps/aarch64/fast-jitter.h | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/alpha/fast-jitter.h   | 34 ++++++++++++++++++++++++++++++++++
> > >  sysdeps/generic/fast-jitter.h | 35 +++++++++++++++++++++++++++++++++++
> > >  sysdeps/s390/fast-jitter.h    | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/sparc/fast-jitter.h   | 33 +++++++++++++++++++++++++++++++++
> > >  sysdeps/x86_64/fast-jitter.h  | 30 ++++++++++++++++++++++++++++++
> > >  6 files changed, 198 insertions(+)
> > >  create mode 100644 sysdeps/aarch64/fast-jitter.h
> > >  create mode 100644 sysdeps/alpha/fast-jitter.h
> > >  create mode 100644 sysdeps/generic/fast-jitter.h
> > >  create mode 100644 sysdeps/s390/fast-jitter.h
> > >  create mode 100644 sysdeps/sparc/fast-jitter.h
> > >  create mode 100644 sysdeps/x86_64/fast-jitter.h
> > >
> > > diff --git a/sysdeps/aarch64/fast-jitter.h b/sysdeps/aarch64/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..fb09d2632c
> > > --- /dev/null
> > > +++ b/sysdeps/aarch64/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on arm with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/alpha/fast-jitter.h b/sysdeps/alpha/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..0a24290eaa
> > > --- /dev/null
> > > +++ b/sysdeps/alpha/fast-jitter.h
> > > @@ -0,0 +1,34 @@
> > > +/* Fast jitter on alpha with rpcc
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  unsigned long int x_;
> > > +  asm volatile ("rpcc %0" : "=r"(x_));
> > > +  /* Don't both with process offset.  We only need jitter not
> > > +     monotonic cycle count.  */
> > > +  return (uint32_t) x;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..63bcf3ccd7
> > > --- /dev/null
> > > +++ b/sysdeps/generic/fast-jitter.h
> > > @@ -0,0 +1,35 @@
> > > +/* Fallback for fast jitter just return 0.
> > > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +/* Baseline just return 0.  We could create jitter using a clock or
> > > +   'random_bits' but that may imply a syscall and the goal of
> > > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > > +   randomness helps performance.  Adding high overhead the function
> > > +   defeats the purpose.  */
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  return 0;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/s390/fast-jitter.h b/sysdeps/s390/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..eb905b1413
> > > --- /dev/null
> > > +++ b/sysdeps/s390/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on s390 with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/sparc/fast-jitter.h b/sysdeps/sparc/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..f4413754c5
> > > --- /dev/null
> > > +++ b/sysdeps/sparc/fast-jitter.h
> > > @@ -0,0 +1,33 @@
> > > +/* Fast jitter on sparc with HP_TIMING_NOW
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +#include <hp-timing.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +}
> > > +
> > > +#endif
> > > diff --git a/sysdeps/x86_64/fast-jitter.h b/sysdeps/x86_64/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..1140f1c295
> > > --- /dev/null
> > > +++ b/sysdeps/x86_64/fast-jitter.h
> > > @@ -0,0 +1,30 @@
> > > +/* X86 use rdtsc to quickly generate pseudo-random for jitter
> > > +   Copyright (C) 2022-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +#include <stdint.h>
> > > +
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +  return __builtin_ia32_rdtsc ();
> >
> > Why can we use HP_TIMING_NOW for x86 as well?  So you then you can use
> > only a generic implementation like:
> >
> > static inline uint32_t
> > get_fast_jitter (void)
> > {
> > #if HP_TIMING_INLINE
> >   hp_timing_t jitter;
> >   HP_TIMING_NOW (jitter);
> >   return (uint32_t) jitter;
> > #else
> >   return 0;
> > #endif
> > }
>
> I'd like this version.  Noah, can you send v2?
>

Fixed in V2, alpha arch will be slower but otherwise should be the same.

> Thanks,

>
> --
> H.J.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-27 20:13 ` [PATCH v2] " Noah Goldstein
@ 2022-04-27 20:46   ` H.J. Lu
  2022-09-11 20:27     ` Sunil Pandey
  0 siblings, 1 reply; 10+ messages in thread
From: H.J. Lu @ 2022-04-27 20:46 UTC (permalink / raw)
  To: Noah Goldstein; +Cc: GNU C Library, Carlos O'Donell

On Wed, Apr 27, 2022 at 1:13 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> 'get_fast_jitter' is meant to be used purely for performance
> purposes. In all cases it's used it should be acceptable to get no
> randomness (see default case). An example use case is in setting
> jitter for retries between threads at a lock. There is a
> performance benefit to having jitter, but only if the jitter can
> be generated very quickly and ultimately there is no serious issue
> if no jitter is generated.
>
> The implementation generally uses 'HP_TIMING_NOW' iff it is
> inlined (avoid any potential syscall paths).
> ---
>  sysdeps/generic/fast-jitter.h | 42 +++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
>  create mode 100644 sysdeps/generic/fast-jitter.h
>
> diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> new file mode 100644
> index 0000000000..4dd53e3475
> --- /dev/null
> +++ b/sysdeps/generic/fast-jitter.h
> @@ -0,0 +1,42 @@
> +/* Fallback for fast jitter just return 0.
> +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _FAST_JITTER_H
> +# define _FAST_JITTER_H
> +
> +# include <stdint.h>
> +# include <hp-timing.h>
> +
> +/* Baseline just return 0.  We could create jitter using a clock or
> +   'random_bits' but that may imply a syscall and the goal of
> +   'get_fast_jitter' is minimal overhead "randomness" when such
> +   randomness helps performance.  Adding high overhead the function
> +   defeats the purpose.  */
> +static inline uint32_t
> +get_fast_jitter (void)
> +{
> +# if HP_TIMING_INLINE
> +  hp_timing_t jitter;
> +  HP_TIMING_NOW (jitter);
> +  return (uint32_t) jitter;
> +# else
> +  return 0;
> +# endif
> +}
> +
> +#endif
> --
> 2.25.1
>

LGTM.    An arch can provide a better one if needed.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.

-- 
H.J.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-04-27 20:46   ` H.J. Lu
@ 2022-09-11 20:27     ` Sunil Pandey
  2022-09-14  1:26       ` Noah Goldstein
  2022-09-29  0:11       ` Noah Goldstein
  0 siblings, 2 replies; 10+ messages in thread
From: Sunil Pandey @ 2022-09-11 20:27 UTC (permalink / raw)
  To: H.J. Lu, Libc-stable Mailing List, Florian Weimer
  Cc: Noah Goldstein, GNU C Library

On Wed, Apr 27, 2022 at 1:47 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Wed, Apr 27, 2022 at 1:13 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > 'get_fast_jitter' is meant to be used purely for performance
> > purposes. In all cases it's used it should be acceptable to get no
> > randomness (see default case). An example use case is in setting
> > jitter for retries between threads at a lock. There is a
> > performance benefit to having jitter, but only if the jitter can
> > be generated very quickly and ultimately there is no serious issue
> > if no jitter is generated.
> >
> > The implementation generally uses 'HP_TIMING_NOW' iff it is
> > inlined (avoid any potential syscall paths).
> > ---
> >  sysdeps/generic/fast-jitter.h | 42 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 42 insertions(+)
> >  create mode 100644 sysdeps/generic/fast-jitter.h
> >
> > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > new file mode 100644
> > index 0000000000..4dd53e3475
> > --- /dev/null
> > +++ b/sysdeps/generic/fast-jitter.h
> > @@ -0,0 +1,42 @@
> > +/* Fallback for fast jitter just return 0.
> > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _FAST_JITTER_H
> > +# define _FAST_JITTER_H
> > +
> > +# include <stdint.h>
> > +# include <hp-timing.h>
> > +
> > +/* Baseline just return 0.  We could create jitter using a clock or
> > +   'random_bits' but that may imply a syscall and the goal of
> > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > +   randomness helps performance.  Adding high overhead the function
> > +   defeats the purpose.  */
> > +static inline uint32_t
> > +get_fast_jitter (void)
> > +{
> > +# if HP_TIMING_INLINE
> > +  hp_timing_t jitter;
> > +  HP_TIMING_NOW (jitter);
> > +  return (uint32_t) jitter;
> > +# else
> > +  return 0;
> > +# endif
> > +}
> > +
> > +#endif
> > --
> > 2.25.1
> >
>
> LGTM.    An arch can provide a better one if needed.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.

I would like to backport this patch to release branch 2.33, 2.34 and 2.35

Any comments/suggestions or objections on this.

commit 911c63a51c690dd1a97dfc587097277029baf00f
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date:   Wed Apr 27 15:13:02 2022 -0500

    sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h

    'get_fast_jitter' is meant to be used purely for performance
    purposes. In all cases it's used it should be acceptable to get no
    randomness (see default case). An example use case is in setting
    jitter for retries between threads at a lock. There is a
    performance benefit to having jitter, but only if the jitter can
    be generated very quickly and ultimately there is no serious issue
    if no jitter is generated.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-09-11 20:27     ` Sunil Pandey
@ 2022-09-14  1:26       ` Noah Goldstein
  2022-09-29  0:11       ` Noah Goldstein
  1 sibling, 0 replies; 10+ messages in thread
From: Noah Goldstein @ 2022-09-14  1:26 UTC (permalink / raw)
  To: Sunil Pandey
  Cc: H.J. Lu, Libc-stable Mailing List, Florian Weimer, GNU C Library

On Sun, Sep 11, 2022 at 1:27 PM Sunil Pandey <skpgkp2@gmail.com> wrote:
>
> On Wed, Apr 27, 2022 at 1:47 PM H.J. Lu via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > On Wed, Apr 27, 2022 at 1:13 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > 'get_fast_jitter' is meant to be used purely for performance
> > > purposes. In all cases it's used it should be acceptable to get no
> > > randomness (see default case). An example use case is in setting
> > > jitter for retries between threads at a lock. There is a
> > > performance benefit to having jitter, but only if the jitter can
> > > be generated very quickly and ultimately there is no serious issue
> > > if no jitter is generated.
> > >
> > > The implementation generally uses 'HP_TIMING_NOW' iff it is
> > > inlined (avoid any potential syscall paths).
> > > ---
> > >  sysdeps/generic/fast-jitter.h | 42 +++++++++++++++++++++++++++++++++++
> > >  1 file changed, 42 insertions(+)
> > >  create mode 100644 sysdeps/generic/fast-jitter.h
> > >
> > > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..4dd53e3475
> > > --- /dev/null
> > > +++ b/sysdeps/generic/fast-jitter.h
> > > @@ -0,0 +1,42 @@
> > > +/* Fallback for fast jitter just return 0.
> > > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +# include <stdint.h>
> > > +# include <hp-timing.h>
> > > +
> > > +/* Baseline just return 0.  We could create jitter using a clock or
> > > +   'random_bits' but that may imply a syscall and the goal of
> > > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > > +   randomness helps performance.  Adding high overhead the function
> > > +   defeats the purpose.  */
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +# if HP_TIMING_INLINE
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +# else
> > > +  return 0;
> > > +# endif
> > > +}
> > > +
> > > +#endif
> > > --
> > > 2.25.1
> > >
> >
> > LGTM.    An arch can provide a better one if needed.
> >
> > Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> >
> > Thanks.
> >
> > --
> > H.J.
>
> I would like to backport this patch to release branch 2.33, 2.34 and 2.35
>
> Any comments/suggestions or objections on this.

Fine by me.
>
> commit 911c63a51c690dd1a97dfc587097277029baf00f
> Author: Noah Goldstein <goldstein.w.n@gmail.com>
> Date:   Wed Apr 27 15:13:02 2022 -0500
>
>     sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
>
>     'get_fast_jitter' is meant to be used purely for performance
>     purposes. In all cases it's used it should be acceptable to get no
>     randomness (see default case). An example use case is in setting
>     jitter for retries between threads at a lock. There is a
>     performance benefit to having jitter, but only if the jitter can
>     be generated very quickly and ultimately there is no serious issue
>     if no jitter is generated.

^ permalink raw reply	[flat|nested] 10+ messages in thread

* Re: [PATCH v2] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
  2022-09-11 20:27     ` Sunil Pandey
  2022-09-14  1:26       ` Noah Goldstein
@ 2022-09-29  0:11       ` Noah Goldstein
  1 sibling, 0 replies; 10+ messages in thread
From: Noah Goldstein @ 2022-09-29  0:11 UTC (permalink / raw)
  To: Sunil Pandey
  Cc: H.J. Lu, Libc-stable Mailing List, Florian Weimer, GNU C Library

On Sun, Sep 11, 2022 at 4:27 PM Sunil Pandey <skpgkp2@gmail.com> wrote:
>
> On Wed, Apr 27, 2022 at 1:47 PM H.J. Lu via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > On Wed, Apr 27, 2022 at 1:13 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > 'get_fast_jitter' is meant to be used purely for performance
> > > purposes. In all cases it's used it should be acceptable to get no
> > > randomness (see default case). An example use case is in setting
> > > jitter for retries between threads at a lock. There is a
> > > performance benefit to having jitter, but only if the jitter can
> > > be generated very quickly and ultimately there is no serious issue
> > > if no jitter is generated.
> > >
> > > The implementation generally uses 'HP_TIMING_NOW' iff it is
> > > inlined (avoid any potential syscall paths).
> > > ---
> > >  sysdeps/generic/fast-jitter.h | 42 +++++++++++++++++++++++++++++++++++
> > >  1 file changed, 42 insertions(+)
> > >  create mode 100644 sysdeps/generic/fast-jitter.h
> > >
> > > diff --git a/sysdeps/generic/fast-jitter.h b/sysdeps/generic/fast-jitter.h
> > > new file mode 100644
> > > index 0000000000..4dd53e3475
> > > --- /dev/null
> > > +++ b/sysdeps/generic/fast-jitter.h
> > > @@ -0,0 +1,42 @@
> > > +/* Fallback for fast jitter just return 0.
> > > +   Copyright (C) 2019-2022 Free Software Foundation, Inc.
> > > +   This file is part of the GNU C Library.
> > > +
> > > +   The GNU C Library is free software; you can redistribute it and/or
> > > +   modify it under the terms of the GNU Lesser General Public
> > > +   License as published by the Free Software Foundation; either
> > > +   version 2.1 of the License, or (at your option) any later version.
> > > +
> > > +   The GNU C Library is distributed in the hope that it will be useful,
> > > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > +   Lesser General Public License for more details.
> > > +
> > > +   You should have received a copy of the GNU Lesser General Public
> > > +   License along with the GNU C Library; if not, see
> > > +   <https://www.gnu.org/licenses/>.  */
> > > +
> > > +#ifndef _FAST_JITTER_H
> > > +# define _FAST_JITTER_H
> > > +
> > > +# include <stdint.h>
> > > +# include <hp-timing.h>
> > > +
> > > +/* Baseline just return 0.  We could create jitter using a clock or
> > > +   'random_bits' but that may imply a syscall and the goal of
> > > +   'get_fast_jitter' is minimal overhead "randomness" when such
> > > +   randomness helps performance.  Adding high overhead the function
> > > +   defeats the purpose.  */
> > > +static inline uint32_t
> > > +get_fast_jitter (void)
> > > +{
> > > +# if HP_TIMING_INLINE
> > > +  hp_timing_t jitter;
> > > +  HP_TIMING_NOW (jitter);
> > > +  return (uint32_t) jitter;
> > > +# else
> > > +  return 0;
> > > +# endif
> > > +}
> > > +
> > > +#endif
> > > --
> > > 2.25.1
> > >
> >
> > LGTM.    An arch can provide a better one if needed.
> >
> > Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> >
> > Thanks.
> >
> > --
> > H.J.
>
> I would like to backport this patch to release branch 2.33, 2.34 and 2.35

Fine by me.
>
> Any comments/suggestions or objections on this.
>
> commit 911c63a51c690dd1a97dfc587097277029baf00f
> Author: Noah Goldstein <goldstein.w.n@gmail.com>
> Date:   Wed Apr 27 15:13:02 2022 -0500
>
>     sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
>
>     'get_fast_jitter' is meant to be used purely for performance
>     purposes. In all cases it's used it should be acceptable to get no
>     randomness (see default case). An example use case is in setting
>     jitter for retries between threads at a lock. There is a
>     performance benefit to having jitter, but only if the jitter can
>     be generated very quickly and ultimately there is no serious issue
>     if no jitter is generated.

^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2022-09-29  0:12 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-04-04 21:39 [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h Noah Goldstein
2022-04-27 16:25 ` Noah Goldstein
2022-04-27 17:47 ` Adhemerval Zanella
2022-04-27 18:04   ` H.J. Lu
2022-04-27 20:13     ` Noah Goldstein
2022-04-27 20:13 ` [PATCH v2] " Noah Goldstein
2022-04-27 20:46   ` H.J. Lu
2022-09-11 20:27     ` Sunil Pandey
2022-09-14  1:26       ` Noah Goldstein
2022-09-29  0:11       ` Noah Goldstein

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