From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752607Ab3ADGu6 (ORCPT ); Fri, 4 Jan 2013 01:50:58 -0500 Received: from mail-wi0-f171.google.com ([209.85.212.171]:41517 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751138Ab3ADGu4 (ORCPT ); Fri, 4 Jan 2013 01:50:56 -0500 X-Greylist: delayed 1059 seconds by postgrey-1.27 at vger.kernel.org; Fri, 04 Jan 2013 01:50:56 EST Message-ID: <50E6764C.9060608@linaro.org> Date: Fri, 04 Jan 2013 07:27:24 +0100 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: rafael.j.wysocki@intel.com CC: Russ Anderson , linux-pm@vger.kernel.org, pdeschrijver@nvidia.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, rja@americas.sgi.com Subject: Re: [PATCH] cpuidle - fix lock contention in the idle path References: <1356516108-11191-1-git-send-email-daniel.lezcano@linaro.org> <20130102211314.GA29447@sgi.com> In-Reply-To: <20130102211314.GA29447@sgi.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/02/2013 10:13 PM, Russ Anderson wrote: > On Wed, Dec 26, 2012 at 11:01:48AM +0100, Daniel Lezcano wrote: >> The commit bf4d1b5ddb78f86078ac6ae0415802d5f0c68f92 introduces >> a lock in the cpuidle_get_cpu_driver function. This function >> is used in the idle_call function. >> >> The problem is the contention with a large number of cpus because >> they try to access the idle routine at the same time. >> >> The lock could be safely removed because of how is used the >> cpuidle api. The cpuidle_register_driver is called first but >> until the cpuidle_register_device is not called we don't >> enter in the cpuidle idle call function because the device >> is not enabled. >> >> The cpuidle_unregister_driver function, leading the a NULL driver, >> is not called before the cpuidle_unregister_device. >> >> This is how is used the cpuidle api from the different drivers. >> >> However, a cleanup around the lock and a proper refcounting >> mechanism should be used to ensure the consistency in the api, >> like cpuidle_unregister_driver should failed if its refcounting >> is not 0. >> >> These modifications will need some code reorganization and rewrite >> which does not fit with a fix. > > I agree. > >> The following patch is a hot fix by returning to the initial behavior >> by removing the lock when getting the driver. > > The patch fixes the problem. Verified on a system with 1024 cpus. > Thanks. > >> Signed-off-by: Daniel Lezcano > > Reported-by: Russ Anderson > Acked-by: Russ Anderson Hi Rafael, could you consider this patch for merging ? Thanks -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog