From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752520AbaFLThN (ORCPT ); Thu, 12 Jun 2014 15:37:13 -0400 Received: from g2t2352.austin.hp.com ([15.217.128.51]:53460 "EHLO g2t2352.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751856AbaFLThM (ORCPT ); Thu, 12 Jun 2014 15:37:12 -0400 Message-ID: <1402601825.2627.5.camel@buesod1.americas.hpqcorp.net> Subject: Re: [PATCH v2 3/4] mutex: Try to acquire mutex only if it is unlocked From: Davidlohr Bueso To: Jason Low Cc: mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, paulmck@linux.vnet.ibm.com, rostedt@goodmis.org, Waiman.Long@hp.com, scott.norton@hp.com, aswin@hp.com Date: Thu, 12 Jun 2014 12:37:05 -0700 In-Reply-To: <1402511843-4721-4-git-send-email-jason.low2@hp.com> References: <1402511843-4721-1-git-send-email-jason.low2@hp.com> <1402511843-4721-4-git-send-email-jason.low2@hp.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.4 (3.6.4-3.fc18) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2014-06-11 at 11:37 -0700, Jason Low wrote: > Upon entering the slowpath in __mutex_lock_common(), we try once more to > acquire the mutex. We only try to acquire if (lock->count >= 0). However, > what we actually want here is to try to acquire if the mutex is unlocked > (lock->count == 1). > > This patch changes it so that we only try-acquire the mutex upon entering > the slowpath if it is unlocked, rather than if the lock count is non-negative. > This helps further reduce unnecessary atomic xchg() operations. > > Furthermore, this patch uses !mutex_is_locked(lock) to do the initial > checks for if the lock is free rather than directly calling atomic_read() > on the lock->count, in order to improve readability. I think this patch can be merged in 2/4, like you had in v1. Otherwise looks good.