Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750763AbWINPTJ (ORCPT ); Thu, 14 Sep 2006 11:19:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750764AbWINPTJ (ORCPT ); Thu, 14 Sep 2006 11:19:09 -0400 Received: from tomts22-srv.bellnexxia.net ([209.226.175.184]:53951 "EHLO tomts22-srv.bellnexxia.net") by vger.kernel.org with ESMTP id S1750763AbWINPTH (ORCPT ); Thu, 14 Sep 2006 11:19:07 -0400 Date: Thu, 14 Sep 2006 11:19:05 -0400 From: Mathieu Desnoyers To: Ingo Molnar , Karim Yaghmour Cc: Roman Zippel , linux-kernel@vger.kernel.org, Christoph Hellwig , Andrew Morton , Ingo Molnar , Greg Kroah-Hartman , Thomas Gleixner , Tom Zanussi , ltt-dev@shafik.org, Michel Dagenais , Douglas Niehaus Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108 Message-ID: <20060914151905.GB29906@Krystal> References: <20060914033826.GA2194@Krystal> <20060914112718.GA7065@elte.hu> <20060914135548.GA24393@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20060914135548.GA24393@elte.hu> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 11:02:51 up 22 days, 12:11, 5 users, load average: 0.21, 0.28, 0.27 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2576 Lines: 63 * Ingo Molnar (mingo@elte.hu) wrote: > > * Roman Zippel wrote: > > the key point is that we want _zero_ "static tracepoints". Firstly, > static tracepoints are fundamentally limited: > > - they can only be added at the source code level > > - modifying them requires a reboot which is not practical in a > production environment Not for kernel modules : unload/load is enough. > - there can only be a limited set of them, while many problems need > finegrained tracepoints tailored to the problem at hand Not true with the dynamic facility loading. LTTng can register new events upon module load/unload. > > - conditional tracepoints are typically either nonexistent or very > limited. > Maybe, but it can be useful to have static instrumentation available for those limited conditional tracepoints. > But besides the usability problems, the most important problem is that > static tracepoints add a _constant maintainance overhead_ to the kernel. > I'm talking from first hand experience: i wrote 'iotrace' (a static > tracer) in 1996 and have maintained it for many years, and even today > i'm maintaining a handful of tracepoints in the -rt kernel. I _dont_ > want static tracepoints in the mainline kernel. > If the trace points are modified with the code by the ones who make the original code changes, it lessens the maintainance overhead. Furthermore, if there is a major change in a code path that requires rethinking the trace points, the person introducing the change has the best knowledge of what to do with the trace point. I think that trace point maintainance should be left to subsystem maintainers, not a centralised task done by distributions once in a while. Talking about experience, Karim has maintained the original LTT trace points, which targeted key kernel event, for years without major trace points changes between kernel versions. I think he already proved that maintainance of static trace points in not an issue. However, I restate that my position is that both static and dynamic instrumentation of the kernel are a necessity and that a tracer core should be usable by both. Mathieu OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/