From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x102d.google.com (mail-pj1-x102d.google.com [IPv6:2607:f8b0:4864:20::102d]) by sourceware.org (Postfix) with ESMTPS id B1EB4385842B for ; Wed, 27 Apr 2022 18:05:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org B1EB4385842B Received: by mail-pj1-x102d.google.com with SMTP id cu23-20020a17090afa9700b001d98d8e53b7so4452398pjb.0 for ; Wed, 27 Apr 2022 11:05:30 -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=z0biuJZhCVu4vxSnMNjW/TeZpdj4XWmrMfull/leZhU=; b=zniyKenPCbpO/wcBQEqcHsku7xFbdzaWUXeyqKtSjxeXVk+2tS3OrSnNh+mEBdxtq1 XTl9eozReSJ1MTUJKvk7QPnjLTqEei0leDL0BsNxEAa8hIex9HVYmn9gIKO44BMkOaLk 84u2UPal+LjvYNh+5IMnlXfWlaDbDHuhMgoGcxH6Osi0uBA1pP0vOZwnwMabcBUvmKSP fLyVgxtKoOJi4k6F5LNSgnNMe9JaRdu3LLsFScLma0iEG9mhXwxCBQALv6pGiD0icb5E pJaX6yO6fdRGFstp93aIaXVxbkizniUCiKwccmy9UMihu38Ao1KS3MWjV6bdwZMXOAuB kEZA== X-Gm-Message-State: AOAM532Y4cYhUQ5UH4ulg+5pfqn7joMUj3zqlOPYAK9vkkDSsKe4Jprl UG5lfZdyU4AHWiuY6yPJqNpsnWqXx9blF3oEmDnrYOVi X-Google-Smtp-Source: ABdhPJzKNsuf9C+2XVxceF8a/gnD1Y/Yb6rLsTBEIowRD+nZqjGJ5rHzOb4ZqhBz3Y/IulvcD/5fGkaBn+KnFxnkAOs= X-Received: by 2002:a17:902:eacd:b0:15c:17fc:31e with SMTP id p13-20020a170902eacd00b0015c17fc031emr28206746pld.4.1651082729475; Wed, 27 Apr 2022 11:05:29 -0700 (PDT) MIME-Version: 1.0 References: <20220404213942.652799-1-goldstein.w.n@gmail.com> In-Reply-To: From: "H.J. Lu" Date: Wed, 27 Apr 2022 11:04:53 -0700 Message-ID: Subject: Re: [PATCH v1] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h To: Adhemerval Zanella Cc: GNU C Library , Noah Goldstein Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3025.7 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 18:05:33 -0000 On Wed, Apr 27, 2022 at 10:48 AM Adhemerval Zanella via Libc-alpha 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 > > + . */ > > + > > +#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 > } I'd like this version. Noah, can you send v2? Thanks, -- H.J.