From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751121AbWFXWPT (ORCPT ); Sat, 24 Jun 2006 18:15:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751122AbWFXWPT (ORCPT ); Sat, 24 Jun 2006 18:15:19 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:32749 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S1751121AbWFXWPR (ORCPT ); Sat, 24 Jun 2006 18:15:17 -0400 Subject: Re: More weird latency trace output (was Re: 2.6.17-rt1) From: Lee Revell To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Steven Rostedt , john stultz In-Reply-To: <1151025892.17952.32.camel@mindpipe> References: <20060618070641.GA6759@elte.hu> <1150937848.2754.379.camel@mindpipe> <1150944663.2754.416.camel@mindpipe> <1151025892.17952.32.camel@mindpipe> Content-Type: text/plain Date: Sat, 24 Jun 2006 18:15:19 -0400 Message-Id: <1151187320.2931.191.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2006-06-22 at 21:24 -0400, Lee Revell wrote: > On Wed, 2006-06-21 at 22:51 -0400, Lee Revell wrote: > > How can the latency tracer be reporting 1898us max latency while the > > trace is of a 12us latency? This must be a bug, correct? > > I've found the bug. The latency tracer uses get_cycles() for > timestamping, which uses rdtsc, which is unusable for timing on dual > core AMD64 machines due to the well known "unsynced TSCs" hardware bug. > > Would a patch to convert the latency tracer to use gettimeofday() be > acceptable? OK, I tried that and it oopses on boot - presumably the latency tracer runs before clocksource infrastructure is initialized. Does anyone have any suggestions at all as to what a proper solution would look like? Is no one interested in this problem? Lee