Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965153AbWIQXO7 (ORCPT ); Sun, 17 Sep 2006 19:14:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965154AbWIQXO7 (ORCPT ); Sun, 17 Sep 2006 19:14:59 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:52908 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S965153AbWIQXO6 (ORCPT ); Sun, 17 Sep 2006 19:14:58 -0400 Date: Mon, 18 Sep 2006 01:06:23 +0200 From: Ingo Molnar To: Nicholas Miell Cc: Paul Mundt , Karim Yaghmour , linux-kernel , Ingo Molnar , Jes Sorensen , Andrew Morton , Roman Zippel , Tom Zanussi , Richard J Moore , "Frank Ch. Eigler" , Michel Dagenais , Mathieu Desnoyers , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , "Martin J. Bligh" Subject: Re: tracepoint maintainance models Message-ID: <20060917230623.GD8791@elte.hu> References: <450D182B.9060300@opersys.com> <20060917112128.GA3170@localhost.usen.ad.jp> <20060917143623.GB15534@elte.hu> <1158524390.2471.49.camel@entropy> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1158524390.2471.49.camel@entropy> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: -2.9 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.9 required=5.9 tests=ALL_TRUSTED,AWL,BAYES_50 autolearn=no SpamAssassin version=3.0.3 -3.3 ALL_TRUSTED Did not pass through any untrusted hosts 0.5 BAYES_50 BODY: Bayesian spam probability is 40 to 60% [score: 0.5000] -0.1 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3044 Lines: 65 * Nicholas Miell wrote: > On my system, Solaris has 49 "real" static probes (with actual > documentation[1]). They are as follows: yeah, _some_ static markers are OK, as long as they are within a dynamic tracing framework! (and are thus constantly "kept in check" by the easy availability of dynamic probes) what is being proposed here is entirely different from dprobes though: Roman suggests that he doesnt want to implement kprobes on his arch, and he wants LTT to remain an _all-static_ tracer. That's the point where i beg to differ: static markers are fine (but they should be kept to a minimum), but generic static /tracers/ need alot more than just a few static markers to be meaningful. So if we accepted static tracers into the kernel, we'd automatically commit (for a long period of time) to a much larger body of static markers - and i'm highly uncomfortable about that. (for the many reasons outlined before) Even if the LTT folks proposed to "compromise" to 50 tracepoints - users of static tracers would likely _not_ be willing to compromise, so there would be a constant (and I say unnecessary) battle going on for the increase of the number of static markers. Static markers, if done for static tracers, have "viral" (Roman: here i mean "auto-spreading", not "disease") properties in that sense - they want to spread to alot larger area of code than they start out from. While if we only have a dynamic tracing framework (which is a mix of static markers and dynamic probes) then pretty much the only user pressure would be: "implement kprobes!". (which is already implemented for 5 major arches and takes only between 500 and 1000 lines of per-arch code for most of them.) ( furthermore, from what you've described it seems to me that kprobes/kretprobes/djprobes+SystemTap is already more capable than dprobes is - hence the number of static markes needed in Linux might in fact be lower in the end than in Solaris. ) > This is the important part: In a dynamic tracing system, the number of > static probes necessary for the tracing system to be useful is > drastically, dramatically, absurdly lower than in a purely static > tracing system. Hell, you don't even need the static probes for it to > be useful, they're just a convenience for events which happen in > multiple places or a high-level name for a low-level implementation > detail. yeah, precisely my point. > In order for the static tracing system to be as useful as the dynamic > system, all of those dynamically generated probe points would have to > be manually added to the kernel. The maintenance burden of this number > of probes is stupidly high. In reality, no static system would ever > reach that level of coverage. yeah, agreed. Ingo - 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/