From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7852) id 5F7B93858437; Thu, 29 Sep 2022 00:48:14 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 5F7B93858437 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1664412494; bh=HPoMXqU+zc9xrfrt6OCO1w8f6t/pfAm7017v3EACY1Q=; h=From:To:Subject:Date:From; b=ZnHah/dGfvSejhsk+N13vU28zDPDsGl4Pe4nsyvCLJnCv6y3jwCWDIb+FX7OaZFaN XxG9VZFq1sKkYtNlKYmGXLUAycUFz7CzjF5at91WlnjFUDlr1XIKJKWcEKWqU3x4iY AyLYRXVHtuLa2qB6V3Ib8Qmp6gDCkvmorjdpHlx0= 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] nptl: Effectively skip CAS in spinlock loop X-Act-Checkin: glibc X-Git-Author: Jangwoong Kim <6812skiii@gmail.com> X-Git-Refname: refs/heads/release/2.33/master X-Git-Oldrev: 60b8295333a076ff853c1093c502c7bf5197ab2e X-Git-Newrev: 8b9ad5ec93ce8941a1e53cc3beea84293d998d2c Message-Id: <20220929004814.5F7B93858437@sourceware.org> Date: Thu, 29 Sep 2022 00:48:14 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8b9ad5ec93ce8941a1e53cc3beea84293d998d2c commit 8b9ad5ec93ce8941a1e53cc3beea84293d998d2c Author: Jangwoong Kim <6812skiii@gmail.com> Date: Tue Dec 14 21:30:51 2021 +0900 nptl: Effectively skip CAS in spinlock loop The commit: "Add LLL_MUTEX_READ_LOCK [BZ #28537]" SHA1: d672a98a1af106bd68deb15576710cd61363f7a6 introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop if atomic load fails. But, "continue" inside of do-while loop does not skip the evaluation of escape expression, thus CAS is not skipped. Replace do-while with while and skip LLL_MUTEX_TRYLOCK if LLL_MUTEX_READ_LOCK fails. Reviewed-by: H.J. Lu (cherry picked from commit 6b8dbbd03ac88f169b65b5c7d7278576a11d2e44) Diff: --- nptl/pthread_mutex_lock.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 2895926953..253743f76c 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -138,10 +138,9 @@ __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); + while (LLL_MUTEX_READ_LOCK (mutex) != 0 + || LLL_MUTEX_TRYLOCK (mutex) != 0); mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8; }