Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753253AbZG1Bx4 (ORCPT ); Mon, 27 Jul 2009 21:53:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752922AbZG1Bxz (ORCPT ); Mon, 27 Jul 2009 21:53:55 -0400 Received: from mail-ew0-f226.google.com ([209.85.219.226]:63909 "EHLO mail-ew0-f226.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752138AbZG1Bxy (ORCPT ); Mon, 27 Jul 2009 21:53:54 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=bhWr2xVr3cCr9VTG+JF7kHxA/ci+BvDmi7qhSCkNYbEgOUbcVjJw2BNnKp4hAgm4HC MNkmeVumWCdAMPHtERjILYfMz9MjlXfwgQJxXEbOL5iDuUVOdqAiD1YSPv4fB5qEbHTC tpiQ9sJ6E8F0WI/kuSE88Heax30jzlaluPDoE= Date: Tue, 28 Jul 2009 03:53:52 +0200 From: Frederic Weisbecker To: KOSAKI Motohiro Cc: Steven Rostedt , Zhaolei , Ingo Molnar , LKML Subject: Re: [PATCH 0/3] Add walltime support for ring-buffer Message-ID: <20090728015351.GF5147@nowhere> References: <4A698F90.90501@cn.fujitsu.com> <20090728103227.D7FB.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090728103227.D7FB.A69D9226@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1819 Lines: 50 On Tue, Jul 28, 2009 at 10:43:11AM +0900, KOSAKI Motohiro wrote: > Hi Zhaolei, > > > Hi Zhaolei, > > > > Could you not just save the wall time in some 64bit format within the > > current timestamp? Right now there's three clocks that can be used by > > ftrace. Two that you can really get two (I need to add access to the > > third). The default clock is sched_clock. But there's an option to get to > > global_clock: > > > > debug/tracing/options/global-clock > > > > # echo 1 > /debug/tracing/options/global-clock > > > > Will enable the global clock. Perhaps we can add a "wall clock" version > > that will map the timestamps to the wall clock? > > > > I really hate adding any more fields to the ring buffer headers. That > > takes away from the amount that you can record per page. > > I think wall-time recording on every event is too slow. slower tracer > isn't useful. > Instead, Can we make pseudo wall-time recording event periodically? > > In nowadays, many workload run on cluster machine environment. Then > We often need compare different machines tracing log. it mean TSC isn't > sufficient. but nobody want performance reduce. > Fortunatelly, ntp time adjustment is not happend so frequently. we > don't need wall-time on _every_ event. > > Thanks. Yeah, that would really slow the tracing. Can't we get a snapshot of the couple (walltime, cpu clock) once at startup. Then we can retrieve the walltime when cpu_clock was 0 and compute the walltime for each traces at output time using the trace timestamp as a delta? Thanks, Frederic. -- 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/