From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754821AbYIVXQ5 (ORCPT ); Mon, 22 Sep 2008 19:16:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753589AbYIVXQt (ORCPT ); Mon, 22 Sep 2008 19:16:49 -0400 Received: from smtp-out.google.com ([216.239.33.17]:5679 "EHLO smtp-out3.google.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753543AbYIVXQs (ORCPT ); Mon, 22 Sep 2008 19:16:48 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=message-id:date:from:to:subject:cc:in-reply-to: mime-version:content-type:content-transfer-encoding: content-disposition:references:x-gmailtapped-by; b=kwyr31QJFn2KRC3pNs5q0KyE6nodJDm+1MU0brXRsPXnA+MiseviEoRr7wLpFRMbO YC+WxRcy9w8bJI82AAv1Q== Message-ID: <33307c790809221616h5e7410f5gc37c262d83722111@mail.gmail.com> Date: Mon, 22 Sep 2008 16:16:41 -0700 From: "Martin Bligh" To: "Masami Hiramatsu" Subject: Re: Unified tracing buffer Cc: "Linux Kernel Mailing List" , "Linus Torvalds" , "Thomas Gleixner" , "Mathieu Desnoyers" , "Steven Rostedt" , od@novell.com, "Frank Ch. Eigler" , systemtap-ml In-Reply-To: <48D81B5F.2030702@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <33307c790809191433w246c0283l55a57c196664ce77@mail.gmail.com> <48D7F5E8.3000705@redhat.com> <33307c790809221313s3532d851g7239c212bc72fe71@mail.gmail.com> <48D81B5F.2030702@redhat.com> X-GMailtapped-By: 172.24.198.101 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >> One thing that I think is still important is to have a unified timestamp >> mechanism on everything, so we can co-ordinate different things back >> together in userspace from different trace tools, so I intend to keep >> that at a lower level, but I think you're right that the event id, etc can >> move up into separate layers. > > I'm not so sure that the unified 'timestamp' must be required by all tracers. > If you just need to merge and sort per-cpu data, you can use an atomic > sequential number for it. > IMHO, the unified 'timestamp' would better be an option, because some > architectures can't support it. I think preparing timestamp-callback > function will help us. An atomic sequential number is: (a) far less meaningful than a timestamp for the user (b) more expensive to compute in many cases. I think we came up with a way to approximate this, using a callback every ms or so as the higher order bits, and a sequential counter in the lower order for those broken platforms. But perhaps it would be better if we started with a discussion of which platforms can't do global timestamps, and why not? I know some of them are fixable, but perhaps not all.