Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757478Ab0LIWVk (ORCPT ); Thu, 9 Dec 2010 17:21:40 -0500 Received: from smtp-out.google.com ([74.125.121.35]:27916 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757360Ab0LIWVi convert rfc822-to-8bit (ORCPT ); Thu, 9 Dec 2010 17:21:38 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=bBm1mNLeD4bra4tNT3imnd4yfYUdoXrsX9uE4/XtG1CshgPeGKmZlfnfNhIzy9Bjks oNBCUe+UYo0gdQDkJ/8w== MIME-Version: 1.0 In-Reply-To: <1291920939.6803.38.camel@twins> References: <20101208142814.GE9777@n2100.arm.linux.org.uk> <1291851079-27061-1-git-send-email-venki@google.com> <1291899120.29292.7.camel@twins> <1291917330.6803.7.camel@twins> <1291920939.6803.38.camel@twins> Date: Thu, 9 Dec 2010 14:21:33 -0800 Message-ID: Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM From: Venkatesh Pallipadi To: Peter Zijlstra Cc: Russell King - ARM Linux , Mikael Pettersson , Ingo Molnar , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, John Stultz Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2450 Lines: 65 On Thu, Dec 9, 2010 at 10:55 AM, Peter Zijlstra wrote: > On Thu, 2010-12-09 at 10:11 -0800, Venkatesh Pallipadi wrote: >> On Thu, Dec 9, 2010 at 9:55 AM, Peter Zijlstra wrote: >> > On Thu, 2010-12-09 at 09:43 -0800, Venkatesh Pallipadi wrote: >> >> >> >> The same problem will be there with below code, with irq_delta > >> >> delta, clock_task can go backwards which is not good. >> >> + ? ? ? delta -= irq_delta; >> >> + ? ? ? rq->clock_task += delta; >> >> >> >> The reason for this is rq->clock and irqtime updates kind of happen >> >> independently and specifically, if a rq->clock update happens while we >> >> are in a softirq, we may have this case of going backwards on the next >> >> update. >> > >> > But how can irq_delta > delta?, we measure it using the same clock. >> > >> >> This would be mostly a corner case like: >> - softirq start time t1 >> - rq->clock updated at t2 and rq->clock_task updated at t2 without >> accounting for current softirq >> - softirq end time t3 >> - cpu spends most time here in softirq or hardirq >> - next rq->clock update at t4 and rq->clock_task update, with delta = >> t4-t2 and irq_delta ~= t4 - t1 > > Ah, something like that would happen when we do a wakeup from > soft/hard-irq context, not an altogether uncommon occurrence. > > Wouldn't that be cured by updating the irq-time when asking for it, > something like the below? (on top of my earlier patch) This should mostly work. There would be a small window there on rq->clock=sched_clock_cpu() and system_vtime doing sched_clock_cpu() and also the overhead of doing this everytime when this going backwards may happen rarely. Thanks, Venki > > --- > Index: linux-2.6/kernel/sched.c > =================================================================== > --- linux-2.6.orig/kernel/sched.c > +++ linux-2.6/kernel/sched.c > @@ -1843,8 +1843,9 @@ void account_system_vtime(struct task_st > ?} > ?EXPORT_SYMBOL_GPL(account_system_vtime); > > -static inline u64 irq_time_cpu(int cpu) > +static u64 irq_time_cpu(int cpu) > ?{ > + ? ? ? account_system_vtime(current); > ? ? ? ?return per_cpu(cpu_softirq_time, cpu) + per_cpu(cpu_hardirq_time, cpu); > ?} > > > -- 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/