public inbox for glibc-cvs@sourceware.org help / color / mirror / Atom feed
From: Sunil Pandey <skpgkp2@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.33/master] Add LLL_MUTEX_READ_LOCK [BZ #28537] Date: Thu, 29 Sep 2022 00:48:04 +0000 (GMT) [thread overview] Message-ID: <20220929004804.28D06385829F@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8844d9b22dfa00675ef4f4e14ffe107a173bc068 commit 8844d9b22dfa00675ef4f4e14ffe107a173bc068 Author: H.J. Lu <hjl.tools@gmail.com> Date: Tue Nov 2 18:33:07 2021 -0700 Add LLL_MUTEX_READ_LOCK [BZ #28537] CAS instruction is expensive. From the x86 CPU's point of view, getting a cache line for writing is more expensive than reading. See Appendix A.2 Spinlock in: https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/xeon-lock-scaling-analysis-paper.pdf The full compare and swap will grab the cache line exclusive and cause excessive cache line bouncing. Add LLL_MUTEX_READ_LOCK to do an atomic load and skip CAS in spinlock loop if compare may fail to reduce cache line bouncing on contended locks. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com> (cherry picked from commit d672a98a1af106bd68deb15576710cd61363f7a6) Diff: --- nptl/pthread_mutex_lock.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 0fd7467b97..ac8a472c08 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -56,6 +56,11 @@ #define FORCE_ELISION(m, s) #endif +#ifndef LLL_MUTEX_READ_LOCK +# define LLL_MUTEX_READ_LOCK(mutex) \ + atomic_load_relaxed (&(mutex)->__data.__lock) +#endif + static int __pthread_mutex_lock_full (pthread_mutex_t *mutex) __attribute_noinline__; @@ -133,6 +138,8 @@ __pthread_mutex_lock (pthread_mutex_t *mutex) break; } atomic_spin_nop (); + if (LLL_MUTEX_READ_LOCK (mutex) != 0) + continue; } while (LLL_MUTEX_TRYLOCK (mutex) != 0);
reply other threads:[~2022-09-29 0:48 UTC|newest] Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20220929004804.28D06385829F@sourceware.org \ --to=skpgkp2@sourceware.org \ --cc=glibc-cvs@sourceware.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).