From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751183AbaFLSZy (ORCPT ); Thu, 12 Jun 2014 14:25:54 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:29438 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716AbaFLSZx (ORCPT ); Thu, 12 Jun 2014 14:25:53 -0400 Message-ID: <1402597547.2627.4.camel@buesod1.americas.hpqcorp.net> Subject: Re: [PATCH v2 4/4] mutex: Optimize mutex trylock slowpath 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 11:25:47 -0700 In-Reply-To: <1402511843-4721-5-git-send-email-jason.low2@hp.com> References: <1402511843-4721-1-git-send-email-jason.low2@hp.com> <1402511843-4721-5-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: > The mutex_trylock() function calls into __mutex_trylock_fastpath() when > trying to obtain the mutex. On 32 bit x86, in the !__HAVE_ARCH_CMPXCHG > case, __mutex_trylock_fastpath() calls directly into __mutex_trylock_slowpath() > regardless of whether or not the mutex is locked. > > In __mutex_trylock_slowpath(), we then acquire the wait_lock spinlock, xchg() > lock->count with -1, then set lock->count back to 0 if there are no waiters, > and return true if the prev lock count was 1. > > However, if the mutex is already locked, then there isn't much point > in attempting all of the above expensive operations. In this patch, we only > attempt the above trylock operations if the mutex is unlocked. > > Signed-off-by: Jason Low This is significantly cleaner than the v1 patch. Reviewed-by: Davidlohr Bueso