From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7852) id 79DDC385829F; Thu, 29 Sep 2022 00:48:19 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 79DDC385829F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1664412499; bh=jslezKZvejmBDy1U+BRoQKdTIGJ/CJ2GLYqIKtNewKw=; h=From:To:Subject:Date:From; b=amn8saxTk2kGxJKjPcza7HKX7QYhMabR7L0Rznjp7pNHdqWOBp2GRPQmWJZGMl64J hPXo/89L3wA1OME7Hqaei7YTvIU4bLbis8PG71KI/GgNUzmNhoaI3lZQjc1gHyJuif 9N+JfI04kEZZwpuyQrDW1kTJt5F2RrolMwHwtPv8= Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Sunil Pandey To: glibc-cvs@sourceware.org Subject: [glibc/release/2.33/master] sysdeps: Add 'get_fast_jitter' interace in fast-jitter.h X-Act-Checkin: glibc X-Git-Author: Noah Goldstein X-Git-Refname: refs/heads/release/2.33/master X-Git-Oldrev: 8b9ad5ec93ce8941a1e53cc3beea84293d998d2c X-Git-Newrev: 870d564e7cd7335734273c8f0fc01a49f5feccc5 Message-Id: <20220929004819.79DDC385829F@sourceware.org> Date: Thu, 29 Sep 2022 00:48:19 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=870d564e7cd7335734273c8f0fc01a49f5feccc5 commit 870d564e7cd7335734273c8f0fc01a49f5feccc5 Author: Noah Goldstein 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. The implementation generally uses 'HP_TIMING_NOW' iff it is inlined (avoid any potential syscall paths). Reviewed-by: H.J. Lu (cherry picked from commit 911c63a51c690dd1a97dfc587097277029baf00f) Diff: --- sysdeps/generic/fast-jitter.h | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) 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 + . */ + +#ifndef _FAST_JITTER_H +# define _FAST_JITTER_H + +# include +# 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) +{ +# if HP_TIMING_INLINE + hp_timing_t jitter; + HP_TIMING_NOW (jitter); + return (uint32_t) jitter; +# else + return 0; +# endif +} + +#endif