From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755098AbYIWCbk (ORCPT ); Mon, 22 Sep 2008 22:31:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754094AbYIWCba (ORCPT ); Mon, 22 Sep 2008 22:31:30 -0400 Received: from tomts20.bellnexxia.net ([209.226.175.74]:56297 "EHLO tomts20-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754841AbYIWCb3 (ORCPT ); Mon, 22 Sep 2008 22:31:29 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AqEEAFTt10hMQWq+/2dsb2JhbACBXbUcgWY Date: Mon, 22 Sep 2008 22:31:15 -0400 From: Mathieu Desnoyers To: Darren Hart Cc: Roland Dreier , Linus Torvalds , Masami Hiramatsu , Martin Bligh , Linux Kernel Mailing List , Thomas Gleixner , Steven Rostedt , "Frank Ch. Eigler" , systemtap-ml Subject: Re: Unified tracing buffer Message-ID: <20080923023115.GE24937@Krystal> References: <33307c790809191433w246c0283l55a57c196664ce77@mail.gmail.com> <48D7F5E8.3000705@redhat.com> <33307c790809221313s3532d851g7239c212bc72fe71@mail.gmail.com> <48D81B5F.2030702@redhat.com> <33307c790809221616h5e7410f5gc37c262d83722111@mail.gmail.com> <48D832B6.3010409@redhat.com> <20080923020216.GC24937@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 22:30:50 up 110 days, 7:11, 7 users, load average: 0.30, 0.24, 0.27 User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Darren Hart (darren@dvhart.com) wrote: > On Mon, Sep 22, 2008 at 7:02 PM, Mathieu Desnoyers > > So only in the specific case of instrumentation of things like locking, > > where it is possible to insure that instrumentation is synchronized with > > the instrumented operation, does it make a difference to choose the TSC > > (which implies a slight delta between the TSCs due to cache line delays > > at synchronization and delay due to TSCs drifts caused by temperature) > > over an atomic increment. > > > > Hrm, i think that overlooks the other reason to use a time based counter over > an atomic increment: you might care about time. Perhaps one might be less > concerned with actual order tightly grouped events and more concerned with the > actual time delta between more temporally distant events. In that case, using > a clocksource would still be valuable. Although admitedtly the caller could > embed that in their payload, but since we seem to agree we need some kind of > counter, the time-based counter appears to be the most flexible. > > Thanks, > See my answer to Linus for a proposal on how to do both :) Mathieu > -- > Darren Hart > -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68