From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756698Ab1LWKxp (ORCPT ); Fri, 23 Dec 2011 05:53:45 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:42779 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756635Ab1LWKxk (ORCPT ); Fri, 23 Dec 2011 05:53:40 -0500 Date: Fri, 23 Dec 2011 11:51:28 +0100 From: Ingo Molnar To: Frank Rowand Cc: Mathieu Desnoyers , Greg KH , "devel@driverdev.osuosl.org" , Peter Zijlstra , "linux-kernel@vger.kernel.org" , "lttng-dev@lists.lttng.org" , Mathieu Desnoyers , Andrew Morton , Linus Torvalds , Thomas Gleixner , Steven Rostedt , Arnaldo Carvalho de Melo Subject: Re: [lttng-dev] [PATCH 09/11] sched: export task_prio to GPL modules Message-ID: <20111223105128.GF4749@elte.hu> References: <1322780830.4699.62.camel@twins> <20111201231751.GA4961@kroah.com> <20111205141749.GC28866@elte.hu> <20111206214446.GD1247@kroah.com> <20111208052354.GC9485@elte.hu> <20111208232709.GA19820@kroah.com> <20111219104915.GA19861@elte.hu> <20111219153053.GA21548@Krystal> <20111220110813.GA19105@elte.hu> <4EF10237.8040700@am.sony.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4EF10237.8040700@am.sony.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=AWL,BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] 0.0 AWL AWL: From: address is in the auto white-list Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Frank Rowand wrote: > On 12/20/11 03:08, Ingo Molnar wrote: > > > > (Cc:-ing Arnaldo on this as well.) > > > > * Mathieu Desnoyers wrote: > > > > < snip > > > > I think your concentration on ABIs is missing a very fundamental > > property of instrumentation: > > > > the life-time and persistence of instrumentation data is > > typically very short ('days' is already an exception - typical > > is minutes, at most hours), and for that reason we havent been > > getting much pressure from users to maintain a perf.data ABI - > > but we are doing it nevertheless. > > > > Instrumentation is fundamentally about the 'here and now' and so > > it fundamentally differs from things like backup formats and > > database formats. An ABI does not hurt and we are maintaining > > it, but you are overrating its importance significantly. > > Just to provide visibility to a different use case... > > The life time of my data is typically weeks, months, or years > (though I am not likely to re-process year old raw data). I'm not saying that it's absolutely never done: for example monitoring/logging on a production box and evaluating events only once per month would certainly qualify. I just say that the overwhelming majority of usecases utilize traces on a short time-span and that we must keep the common usecase in mind when supporting not so common usecases. It's the same deal as with -rt: compared to the 'normal' usage of Linux -rt is somewhat of a special case - yet it's still something very much worth doing, as long as the main usecase is always kept in mind. Thanks, Ingo