From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-x112f.google.com (mail-yw1-x112f.google.com [IPv6:2607:f8b0:4864:20::112f]) by sourceware.org (Postfix) with ESMTPS id 958C7385742B for ; Wed, 27 Apr 2022 16:25:44 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 958C7385742B Received: by mail-yw1-x112f.google.com with SMTP id 00721157ae682-2ef5380669cso24773427b3.9 for ; Wed, 27 Apr 2022 09:25:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ncDTQec44/w+Mxx13HRviQ3b81/2y1gooYKT62Z3/4Y=; b=I1gu2hLrDrIBN45I5/JBet15DQKdi7QdLfgoVaX1TON6KWN7upN4dTQKhWgbGxibfi nhbdd5DWDFosjw9gNV2JqWb1hqH6nyTxKqknTSSmFHZNytzggL+toRNQsfLb8ZZwKFIB z1nkWo37i5GVcbrTBdJy3BEG062ymw9jRyGeR7V57zp43fUgVqDzrQ0DGVMahqq/Cmnf XNnW1vrNaMKdZodU05jdp1HpuDXQ5I5y38Griun29SRcLAReyki7s3yYOJvq8uxvSLjQ i4TmqeaOJpUAA4+7lb8gc112g0n7ny4CGtjA1Rjqwsqd7nXyjQw/ICYN5IepS6a8R95x Mfsg== X-Gm-Message-State: AOAM5312ljwudRrnfWEriAwtVyZ80MJjeivpSTJdu75JDOWKNxUsBy9W Tp+ynugJ+I8fPvfO3t4ZWZiCWVq0CQ68RQwLPgDwbHzo X-Google-Smtp-Source: ABdhPJzQ3rYAlB4UP+HHCfOrdfeD8qJVVELl8M3Ur7x01exLyaS9sSS5oQQ04y+n8b2FU3BCYL5J658hYt9VGpxefQU= X-Received: by 2002:a81:c44b:0:b0:2d6:4726:ef4b with SMTP id s11-20020a81c44b000000b002d64726ef4bmr28259900ywj.184.1651076743848; Wed, 27 Apr 2022 09:25:43 -0700 (PDT) MIME-Version: 1.0 References: <20220404213942.652799-1-goldstein.w.n@gmail.com> In-Reply-To: <20220404213942.652799-1-goldstein.w.n@gmail.com> From: Noah Goldstein Date: Wed, 27 Apr 2022 11:25:33 -0500 Message-ID: Subject: Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h To: GNU C Library Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-7.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, KAM_SHORT, 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 16:25:46 -0000 On Mon, Apr 4, 2022 at 4:39 PM Noah Goldstein 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 > + . */ > + > +#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 (); > +} > + > +#endif > -- > 2.25.1 > Ping.