Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754174Ab3JBP5V (ORCPT ); Wed, 2 Oct 2013 11:57:21 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:41439 "EHLO mail-lb0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753662Ab3JBP5S (ORCPT ); Wed, 2 Oct 2013 11:57:18 -0400 MIME-Version: 1.0 In-Reply-To: <1380709565-22153-1-git-send-email-daniel.lezcano@linaro.org> References: <1380709565-22153-1-git-send-email-daniel.lezcano@linaro.org> Date: Wed, 2 Oct 2013 17:57:17 +0200 Message-ID: Subject: Re: [PATCH V2] tick: Make sleep length calculation more accurate From: Frederic Weisbecker To: Daniel Lezcano Cc: Thomas Gleixner , Stephen Boyd , LKML , patches@linaro.org, "linaro-kernel@lists.linaro.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1600 Lines: 44 2013/10/2 Daniel Lezcano : > The sleep_length is computed in the tick_nohz_stop_sched_tick function but it > is used later in the code with in between the local irq enabled. > > cpu_idle_loop > tick_nohz_idle_enter [ exits with local irq enabled ] > __tick_nohz_idle_enter > tick_nohz_stop_sched_tick > ... > > arch_cpu_idle > menu_select [ uses here 'sleep_length' ] > ... > > Between the computation of the sleep length and its usage, some interrupts > may occur, making the sleep length shorter than actually it is because of the > interrupt processing So, do you mean that the ts->sleep_length would return a value that is too long given that the CPU already spent some time to service the irqs since we computed the sleep length in tick_nohz_idle_enter()? But then tick_nohz_irq_exit() should take care of that as it calls again tick_nohz_stop_sched_tick(). So I'm a bit confused. > or different if the timer itself expired. Same here, if the timer expired, it triggers an interrupt which can do two things: 1) reprogram a new timer and this recompute sleep_length 2) set_need_resched() and then exit the idle loop, so arch_cpu_idle() won't even be called. Or the timer interrupts hlt, but then menu_select() was called before. So I probably missed something here. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/