From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762758AbdAEPSk (ORCPT ); Thu, 5 Jan 2017 10:18:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:25455 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180AbdAEPSU (ORCPT ); Thu, 5 Jan 2017 10:18:20 -0500 Subject: Re: [PATCH v2] locking/pvqspinlock: Relax cmpxchg's to improve performance on some archs To: Pan Xinhui , Peter Zijlstra References: <1482697561-23848-1-git-send-email-longman@redhat.com> <20170103161836.GY3107@twins.programming.kicks-ass.net> <20170104094149.GD25813@worktop.programming.kicks-ass.net> <006322ad-2e72-c8fe-361f-233f1821063a@linux.vnet.ibm.com> Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Boqun Feng From: Waiman Long Organization: Red Hat Message-ID: <349c5926-cd35-2313-b8a0-ebfe6eb5e4a0@redhat.com> Date: Thu, 5 Jan 2017 10:17:46 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <006322ad-2e72-c8fe-361f-233f1821063a@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 05 Jan 2017 15:17:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/05/2017 03:16 AM, Pan Xinhui wrote: > > > 在 2017/1/4 17:41, Peter Zijlstra 写道: >> On Tue, Jan 03, 2017 at 05:07:54PM -0500, Waiman Long wrote: >>> On 01/03/2017 11:18 AM, Peter Zijlstra wrote: >>>> On Sun, Dec 25, 2016 at 03:26:01PM -0500, Waiman Long wrote: >>>>> A number of cmpxchg calls in qspinlock_paravirt.h were replaced by >>>>> more >>>>> relaxed versions to improve performance on architectures that use >>>>> LL/SC. >>>> Claim without numbers ;-) >>> >>> Well it is hard to produce actual numbers here as I don't have the >>> setup >>> to gather data. >> >> Surely RHT has big PPC machines around? I know that getting to them is a >> wee bit of a bother, but they should be available somewhere. >> > hi, > > I do some tests about cmpxchg and cmpxchg_acquire before on ppc. > > loops in 15s of each cmpxchg is below. > > cmpxchg_relaxed: 336663 > cmpxchg_release: 369054 > cmpxchg_acquire: 363364 > cmpxchg: 179435 > > so cmpxchg is really expensive than others. > but I also have doubt about the cmpxchg_relaxed, it should be the > cheapest, but from the tests, release/acquire are faster than it. > > thanks > xinhui > Thanks for doing the test. It looks like we should just focus on using either cmpxchg_release or cmpxchg_acquire and forget about cmpxchg_relaxed. Cheers, Longman