From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7852) id 95682385782C; Wed, 28 Sep 2022 16:06:14 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 95682385782C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1664381174; bh=u2nma9EF+qe+HTmPA+qb6mugkkqeaebZSoUm6TaIeaY=; h=From:To:Subject:Date:From; b=Ss6F4dZB6x/RqQReSnrFKmUDhC54nuxIgTiMo5Oj6aXgAb4QwaiJ8x2hCzLfDPha+ P74p6nMFtcoYTxSWog8jK1QH2O/NknL8JgK29RP3yNaGkoH7zxTfCW3/cW6Kw2Yeq5 g3LEioY5ogHPlznqdvMhI8MdNcuQFAP2PUuy8FdQ= 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/2.34/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/2.34/master X-Git-Oldrev: 6bcfbee7277e4faa4b693bd965931f0d1883005d X-Git-Newrev: 43760d33d78f9ea8c8af942b570112ee801b99df Message-Id: <20220928160614.95682385782C@sourceware.org> Date: Wed, 28 Sep 2022 16:06:14 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=43760d33d78f9ea8c8af942b570112ee801b99df commit 43760d33d78f9ea8c8af942b570112ee801b99df 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 49901ffa0a..bbe754a272 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -147,10 +147,9 @@ 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; }