From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751281AbWFXXtM (ORCPT ); Sat, 24 Jun 2006 19:49:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751280AbWFXXtM (ORCPT ); Sat, 24 Jun 2006 19:49:12 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:40330 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S1751279AbWFXXtK (ORCPT ); Sat, 24 Jun 2006 19:49:10 -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: <20060624221235.GA23423@elte.hu> References: <20060618070641.GA6759@elte.hu> <1150937848.2754.379.camel@mindpipe> <1150944663.2754.416.camel@mindpipe> <1151025892.17952.32.camel@mindpipe> <1151187320.2931.191.camel@mindpipe> <20060624221235.GA23423@elte.hu> Content-Type: text/plain Date: Sat, 24 Jun 2006 19:49:12 -0400 Message-Id: <1151192953.2931.208.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 Sun, 2006-06-25 at 00:12 +0200, Ingo Molnar wrote: > * Lee Revell wrote: > > The latency tracer uses get_cycles() for > > > timestamping, which uses rdtsc, which is unusable for timing on dual > > > core AMD64 machines > does it get better if you boot with idle=poll? [that could work around > the rdtsc drifting problem] Calling gettimeofday() from within the > tracer is close to impossible - way too many opportunities for > recursion. It's also pretty slow that way. That seemed to solve the drifting problem, but I still get some weird behavior. The max reported trace in dmesg still does not match /proc/latency_trace: ( posix_cpu_timer-3 |#0): new 38 us maximum-latency wakeup. preemption latency trace v1.1.5 on 2.6.17-rt1-smp-latency-trace -------------------------------------------------------------------- latency: 19 us, #74/74, CPU#0 | (M:rt VP:0, KP:0, SP:1 HP:1 #P:2) ----------------- | task: posix_cpu_timer-3 (uid:0 nice:0 policy:1 rt_prio:99) ----------------- Lee