From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7852) id A8CC03857345; Wed, 28 Sep 2022 19:11:16 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org A8CC03857345 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1664392276; bh=hzeqVzh+wQIV1qvL9Y7BNUrqHwfL7IaV4+gr9gtbDV8=; h=From:To:Subject:Date:From; b=QiZOou2S+UaXhsum113nkB1ltQi2+olZ3jjDT5X641hr7KUKXMH3jdRWMsjTibP4w zkveZae8HtT3505wP/hinc9QneFGMgwrHLxEx4Z6oZnJMPvPZNEs+nBOEMm2TUQaeQ UL27LtWpx0fV7DEIBI2BbMVTYeZNm2CwsukC9Dw0= 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/users/skpgkp2/2.33/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/users/skpgkp2/2.33/master X-Git-Oldrev: 520639f146eecc5baee7b0a9fc8fc3f416bcbd68 X-Git-Newrev: 2574fdfc0f7ed7fe2586bd906e6076912af6cd86 Message-Id: <20220928191116.A8CC03857345@sourceware.org> Date: Wed, 28 Sep 2022 19:11:16 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2574fdfc0f7ed7fe2586bd906e6076912af6cd86 commit 2574fdfc0f7ed7fe2586bd906e6076912af6cd86 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; }