From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753860AbYI3Sfm (ORCPT ); Tue, 30 Sep 2008 14:35:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752936AbYI3Sfd (ORCPT ); Tue, 30 Sep 2008 14:35:33 -0400 Received: from tomts43.bellnexxia.net ([209.226.175.110]:48184 "EHLO tomts43-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752835AbYI3Sfd (ORCPT ); Tue, 30 Sep 2008 14:35:33 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AhUFAHAO4khMQWq+/2dsb2JhbACBZr4PgWk Date: Tue, 30 Sep 2008 14:35:31 -0400 From: Mathieu Desnoyers To: Steven Rostedt Cc: Martin Bligh , Peter Zijlstra , linux-kernel@vger.kernel.org, prasad@linux.vnet.ibm.com, Linus Torvalds , Thomas Gleixner , od@suse.com, "Frank Ch. Eigler" , Andrew Morton , hch@lst.de, David Wilder , Tom Zanussi Subject: Re: [RFC PATCH] LTTng relay buffer allocation, read, write Message-ID: <20080930183531.GA20670@Krystal> References: <20080927134012.GA11930@Krystal> <1222535419.16700.300.camel@lappy.programming.kicks-ass.net> <20080929155004.GA11029@Krystal> <1222709445.23876.70.camel@twins.programming.kicks-ass.net> <20080929203124.GA23070@Krystal> <33307c790809301022q2821ecc7iabf41eb513707e0c@mail.gmail.com> <33307c790809301023v1b0755fbsab1bbfa9bfaad58@mail.gmail.com> <20080930181436.GA19690@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: 14:30:19 up 117 days, 23:10, 9 users, load average: 0.47, 0.39, 0.44 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 * Steven Rostedt (rostedt@goodmis.org) wrote: > > On Tue, 30 Sep 2008, Mathieu Desnoyers wrote: > > > > In Steven's scheme, the event IDs in the 4 bytes are reserved for > > (useless) internal use ;) They can therefore not be used for specific > > tracer event IDs, which I think is a misuse of the precious bits > > otherwise available to store really useful event IDs. > > I'm using them, so they must not be totally useless. ;-) > > But ftrace has its own event ids and I don't want the ring buffer to ever > have to know about them. > > -- Steve > You are actually using them to put redundant information that could be encoded differently and thus save 4 bits per event records, more or less what will be needed by most tracers (15 IDs, 1 reserved for an extended ID field). So the fact that you use them does not mean they are really required, and I don't think such duplicated information actually makes things more solid. Maybe just more obscure ? Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68