From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752644AbaE0UWn (ORCPT ); Tue, 27 May 2014 16:22:43 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:43266 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752108AbaE0UWl (ORCPT ); Tue, 27 May 2014 16:22:41 -0400 Message-ID: <5384F410.6000604@codeaurora.org> Date: Tue, 27 May 2014 13:22:40 -0700 From: Stephen Boyd User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Arnd Bergmann CC: Corey Minyard , linux-rt-users@vger.kernel.org, minyard@acm.org, Stanislav Meduna , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm: Set hardirq tracing to on when idling References: <1401045323-7116-1-git-send-email-minyard@acm.org> <6082113.tHepRBe99K@wuerfel> <5384E892.90808@codeaurora.org> <10128642.DD2TJ8Ps9I@wuerfel> In-Reply-To: <10128642.DD2TJ8Ps9I@wuerfel> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/27/14 12:39, Arnd Bergmann wrote: > On Tuesday 27 May 2014 12:33:38 Stephen Boyd wrote: >> On 05/27/14 12:27, Arnd Bergmann wrote: >>> On Tuesday 27 May 2014 11:53:59 Stephen Boyd wrote: >>>> On 05/27/14 11:49, Arnd Bergmann wrote: >>>>> You also commented in that thread about stop_critical_timings()/ >>>>> start_critical_timings(). Corey, can you look at that, too? I >>>>> think it's designed to avoid the issue you are seeing but >>>>> for some reason doesn't. >>>> I sent a patch last week to "solve" this problem. I'm not sure if it's >>>> right but it works for me. >>>> >>>> https://lkml.org/lkml/2014/5/19/607 >>> I think that one was also wrong, as the intention of the existing >>> stop_critical_timings() function is already to do the same that >>> Corey's patch does, i.e. stop the trace before we go to idle as >>> if we were turning IRQs on. >> stop_critical_timings() is called in the generic idle loop. It looks >> like stop_critical_timings() just isn't written correctly. All it does >> is turn off the tracer, but it doesn't prevent future calls to >> spinlocks, etc. from causing the tracer to turn on again between calls >> to stop/start_critical_timings(). It seems better to prevent any more >> tracing from happening between a call to stop_critical_timings() and >> start_critical_timings() so we don't have to litter calls to that >> function throughout the idle path. > But are there any such calls in the idle function? I understand what > you are doing in your patch, but I don't see why you have to actually > do it. > Yes in my build it happens immediately after in rcu_enter_idle(). It would also happen if you had a cpuidle driver that notified the core that the timers stop during idle (FEAT_C3_STOP). In that case we would call clockevents_notify() which will call raw_spin_lock_irqsave(). -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation