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([2804:431:c7ca:4214:b613:182d:cdde:5f86]) by smtp.gmail.com with ESMTPSA id k4-20020a9d7604000000b00605d52c6472sm1396320otl.9.2022.04.27.10.47.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Apr 2022 10:47:44 -0700 (PDT) Message-ID: Date: Wed, 27 Apr 2022 14:47:42 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h Content-Language: en-US To: libc-alpha@sourceware.org, Noah Goldstein References: <20220404213942.652799-1-goldstein.w.n@gmail.com> From: Adhemerval Zanella In-Reply-To: <20220404213942.652799-1-goldstein.w.n@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-14.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_SHORT, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Apr 2022 17:47:49 -0000 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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > +#include > + > +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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > + > +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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > + > +/* 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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > +#include > + > +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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > +#include > + > +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 > + . */ > + > +#ifndef _FAST_JITTER_H > +# define _FAST_JITTER_H > + > +#include > + > +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 }