From: Noah Goldstein <goldstein.w.n@gmail.com>
To: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h
Date: Wed, 27 Apr 2022 11:25:33 -0500 [thread overview]
Message-ID: <CAFUsyfJdsxxYNTM0NUNJTH9iejfs3PG3Bgq1+6Pdtb=3THuAmA@mail.gmail.com> (raw)
In-Reply-To: <20220404213942.652799-1-goldstein.w.n@gmail.com>
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.
next prev parent reply other threads:[~2022-04-27 16:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-04 21:39 Noah Goldstein
2022-04-27 16:25 ` Noah Goldstein [this message]
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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