From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753455AbZBDFzw (ORCPT ); Wed, 4 Feb 2009 00:55:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751120AbZBDFzo (ORCPT ); Wed, 4 Feb 2009 00:55:44 -0500 Received: from casper.infradead.org ([85.118.1.10]:49571 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbZBDFzo (ORCPT ); Wed, 4 Feb 2009 00:55:44 -0500 Date: Tue, 3 Feb 2009 21:55:52 -0800 From: Arjan van de Ven To: Andrew Morton Cc: Corrado Zoccolo , linux-kernel@vger.kernel.org Subject: Re: Negative values in /proc/latency_stats Message-ID: <20090203215552.38193470@infradead.org> In-Reply-To: <20090203214609.39c9c6b2.akpm@linux-foundation.org> References: <4e5e476b0901310542n796dafbem5c656da07a2f8a56@mail.gmail.com> <20090202205545.4e1a32ea.akpm@linux-foundation.org> <20090203161648.361a924a@infradead.org> <20090203214609.39c9c6b2.akpm@linux-foundation.org> Organization: Intel X-Mailer: Claws Mail 3.7.0 (GTK+ 2.14.5; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 3 Feb 2009 21:46:09 -0800 > > + * (note: the average latency is the acummulated latency deviced > > by the number > > + * of times) > > I was surprised at this. Is the stack backtracer sufficiently > reliable/repeatable for this to work? yep it is, at least on x86 and x86-64. > > > + * Negative latencies (caused by time going backwards) are also > > explicitly > > + * skipped. > > Are we sure that this was the cause of the problem? not 100%, but if you add only positive numbers..... the only other option is an overflow.. but that would be such a huge latency that that is not very believable. > > Which time source is the caller using here, and why is it going > backwards? scheduler clock. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org