Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757875Ab0LMPDS (ORCPT ); Mon, 13 Dec 2010 10:03:18 -0500 Received: from mail-iw0-f180.google.com ([209.85.214.180]:54979 "EHLO mail-iw0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753652Ab0LMPDR convert rfc822-to-8bit (ORCPT ); Mon, 13 Dec 2010 10:03:17 -0500 X-Greylist: delayed 1487 seconds by postgrey-1.27 at vger.kernel.org; Mon, 13 Dec 2010 10:03:16 EST DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=IsRxR8bqeajCZfMWehzekBZZKsi2Qhirtrn2kE9xhBMJsbIDzMc8GIpQo8X2fc61IF BFBWJBQDsrHD4KHv4uaiNhpJ36Ywew6UAmIyop7vOTyOV/JDTvjGEVGyWOHw9LiuI6kJ hFGTYsulQpJ/D/3BmYMvnibQ17mLggZHrq5yE= MIME-Version: 1.0 In-Reply-To: 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> Date: Mon, 13 Dec 2010 20:03:02 +0530 Message-ID: Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM From: Jack Daniel To: Venkatesh Pallipadi Cc: Peter Zijlstra , 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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1616 Lines: 38 On Thu, Dec 9, 2010 at 11:41 PM, 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 ^^^ I was curious on this line. Shouldn't this be irq_delta ~= t3 - t1 ? If so the time going backwards shouldn't happen. If it does happen then wouldn't it be better to program irq_time_cpu(cpu_of(rq)) to return t3 instead of t4? Thanks, Jack -- 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/