From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755900Ab3IZITW (ORCPT ); Thu, 26 Sep 2013 04:19:22 -0400 Received: from mail-wg0-f46.google.com ([74.125.82.46]:39224 "EHLO mail-wg0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751550Ab3IZITT (ORCPT ); Thu, 26 Sep 2013 04:19:19 -0400 Message-ID: <5243EE02.9020207@linaro.org> Date: Thu, 26 Sep 2013 10:19:14 +0200 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Viresh Kumar CC: "Rafael J. Wysocki" , Lists linaro-kernel , Patch Tracking , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List Subject: Re: [PATCH 19/21] cpuidle: create list of registered drivers References: <7e9565e323c1e065eeb2a2a1075967bd21ee6066.1379779777.git.viresh.kumar@linaro.org> <5243641B.6050604@linaro.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/26/2013 08:17 AM, Viresh Kumar wrote: > On 26 September 2013 04:00, Daniel Lezcano wrote: >> If you introduce a list, you will have to introduce a lock to protect >> it. > > I missed it, should have added that :) > >> This lock will be in the fast path cpuidle_idle_call with the >> get_driver function and conforming to the comment: "NOTE: no locks or >> semaphores should be used here". >> >> A lock has been introduced in this function already and the system hangs >> with 1024 cpus. > > Hmm... I see.. I didn't knew about this expectation.. What about a rcu > read/write lock? As far as I know its too lightweight... Can we have that > in fast path? Nope, we can't use rcu in the idle path :) http://lists.infradead.org/pipermail/linux-arm-kernel/2012-February/083054.html -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog