From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26821 invoked by alias); 23 Sep 2008 02:32:20 -0000 Received: (qmail 26813 invoked by uid 22791); 23 Sep 2008 02:32:20 -0000 X-Spam-Status: No, hits=-2.4 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from tomts25-srv.bellnexxia.net (HELO tomts25-srv.bellnexxia.net) (209.226.175.188) by sourceware.org (qpsmtpd/0.31) with ESMTP; Tue, 23 Sep 2008 02:31:39 +0000 Received: from toip3.srvr.bell.ca ([209.226.175.86]) by tomts25-srv.bellnexxia.net (InterMail vM.5.01.06.13 201-253-122-130-113-20050324) with ESMTP id <20080923023115.MTIP1557.tomts25-srv.bellnexxia.net@toip3.srvr.bell.ca> for ; Mon, 22 Sep 2008 22:31:15 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AqEEAOXv10hMQWq+/2dsb2JhbACBXbUXgWY Received: from bas5-montreal19-1279355582.dsl.bell.ca (HELO krystal.dyndns.org) ([76.65.106.190]) by toip3.srvr.bell.ca with ESMTP; 22 Sep 2008 22:26:49 -0400 Received: from localhost (localhost [127.0.0.1]) (uid 1000) by krystal.dyndns.org with local; Mon, 22 Sep 2008 22:31:15 -0400 id 0017AAA5.48D854F3.00006CD9 Date: Tue, 23 Sep 2008 02:32:00 -0000 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) X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2008-q3/txt/msg00745.txt.bz2 * 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