From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754693AbYI3Tyb (ORCPT ); Tue, 30 Sep 2008 15:54:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753880AbYI3TyO (ORCPT ); Tue, 30 Sep 2008 15:54:14 -0400 Received: from tomts36.bellnexxia.net ([209.226.175.93]:34910 "EHLO tomts36-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753820AbYI3TyM (ORCPT ); Tue, 30 Sep 2008 15:54:12 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AhUFAHwg4khMQWq+/2dsb2JhbACBZr1XgWk Date: Tue, 30 Sep 2008 15:54:09 -0400 From: Mathieu Desnoyers To: Martin Bligh Cc: Steven Rostedt , 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: <20080930195409.GA24169@Krystal> References: <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> <20080930183531.GA20670@Krystal> <33307c790809301244x40218be6of61b53104b8d7da3@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <33307c790809301244x40218be6of61b53104b8d7da3@mail.gmail.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 15:48:36 up 118 days, 29 min, 10 users, load average: 0.40, 0.57, 0.50 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 * Martin Bligh (mbligh@google.com) wrote: > > 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). > > You have 15 event types that are useful with no data payload at all? > I am not saying anything about the actual number of events with 0 bytes payload I actually have in my own instrumentation, if this is what you mean. I am just saying that it leaves this room available for such events. Even if there is a 32 bits payload associated with those events, the fact that we can encode the event ID in the 32 bits header will bring those events from 96 bits (due to 32 bits alignment) down to 64 bits. > > 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 ? > > This is all over 1 bit of information, right? Since you need at least 1 for > the timestamp stuff. 4 bits of information could be added to the 32-bits header if we allow tracers to register their first 15 event IDs in those 4 bits. But well... let's keep that for v2. ;) Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68