From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932571AbeD0Jlu (ORCPT ); Fri, 27 Apr 2018 05:41:50 -0400 Received: from terminus.zytor.com ([198.137.202.136]:49379 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932282AbeD0Jlr (ORCPT ); Fri, 27 Apr 2018 05:41:47 -0400 Date: Fri, 27 Apr 2018 02:41:25 -0700 From: tip-bot for Will Deacon Message-ID: Cc: tglx@linutronix.de, hpa@zytor.com, mingo@kernel.org, longman@redhat.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, peterz@infradead.org, torvalds@linux-foundation.org Reply-To: tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com, peterz@infradead.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, longman@redhat.com, will.deacon@arm.com In-Reply-To: <1524738868-31318-10-git-send-email-will.deacon@arm.com> References: <1524738868-31318-10-git-send-email-will.deacon@arm.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node Git-Commit-ID: c131a198c497db436b558ac5e9a140cdcb91b304 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: c131a198c497db436b558ac5e9a140cdcb91b304 Gitweb: https://git.kernel.org/tip/c131a198c497db436b558ac5e9a140cdcb91b304 Author: Will Deacon AuthorDate: Thu, 26 Apr 2018 11:34:23 +0100 Committer: Ingo Molnar CommitDate: Fri, 27 Apr 2018 09:48:50 +0200 locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node When a locker reaches the head of the queue and takes the lock, a concurrent locker may enqueue and force the lock holder to spin whilst its node->next field is initialised. Rather than open-code a READ_ONCE/cpu_relax() loop, this can be implemented using smp_cond_load_relaxed() instead. Signed-off-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Cc: Linus Torvalds Cc: Thomas Gleixner Cc: boqun.feng@gmail.com Cc: linux-arm-kernel@lists.infradead.org Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1524738868-31318-10-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar --- kernel/locking/qspinlock.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 56af1fa9874d..d6c3b029bd93 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -483,10 +483,8 @@ locked: /* * contended path; wait for next if not observed yet, release. */ - if (!next) { - while (!(next = READ_ONCE(node->next))) - cpu_relax(); - } + if (!next) + next = smp_cond_load_relaxed(&node->next, (VAL)); arch_mcs_spin_unlock_contended(&next->locked); pv_kick_node(lock, next);