Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756725Ab0LISLi (ORCPT ); Thu, 9 Dec 2010 13:11:38 -0500 Received: from smtp-out.google.com ([74.125.121.35]:52386 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755581Ab0LISLh convert rfc822-to-8bit (ORCPT ); Thu, 9 Dec 2010 13:11:37 -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=TnCWE7caeUrBdF9ttb7LXD6k3u9GojDHxe5q1c4V9iRiWob/Ku+DbLEM5GEXXOvqjk 3ma7QeVTo3DTozM36Rtg== MIME-Version: 1.0 In-Reply-To: <1291917330.6803.7.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> Date: Thu, 9 Dec 2010 10:11:33 -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: 1225 Lines: 29 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 -- 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/