Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751842AbWIRQkm (ORCPT ); Mon, 18 Sep 2006 12:40:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751844AbWIRQkl (ORCPT ); Mon, 18 Sep 2006 12:40:41 -0400 Received: from [81.2.110.250] ([81.2.110.250]:28316 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1751842AbWIRQkk (ORCPT ); Mon, 18 Sep 2006 12:40:40 -0400 Subject: Re: tracepoint maintainance models From: Alan Cox To: Ingo Molnar Cc: "Frank Ch. Eigler" , Paul Mundt , Mathieu Desnoyers , linux-kernel , Jes Sorensen , Andrew Morton , Tom Zanussi , Richard J Moore , Michel Dagenais , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , "Martin J. Bligh" In-Reply-To: <20060918161511.GA21204@elte.hu> References: <20060917143623.GB15534@elte.hu> <20060917153633.GA29987@Krystal> <20060918000703.GA22752@elte.hu> <450DF28E.3050101@opersys.com> <20060918011352.GB30835@elte.hu> <20060918122527.GC3951@redhat.com> <20060918150231.GA8197@elte.hu> <1158594491.6069.125.camel@localhost.localdomain> <20060918152230.GA12631@elte.hu> <1158596341.6069.130.camel@localhost.localdomain> <20060918161511.GA21204@elte.hu> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Mon, 18 Sep 2006 18:02:10 +0100 Message-Id: <1158598930.6069.143.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 (2.6.2-1.fc5.5) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1255 Lines: 28 Ar Llu, 2006-09-18 am 18:15 +0200, ysgrifennodd Ingo Molnar: > Do you consider a single 5-byte NOP for a judiciously chosen 50 places > in the kernel unacceptable? Note that the argument has shifted from Its not neccessary. The question about acceptability doesn't come up. > static tracers to dynamic tracers: this _is_ about SystemTap: it adds > points to the kernel where we can _guarantee_ that a dynamic probe can > be inserted. That already exists. You don't always know the address of the point. Knowing where to stick the probe is out of line, shoving nops in the code is an ugly unneccessary hack. You can't really have it both ways - you argued that the performance improvement for LTT static traces wasn't justification and pointed out jprobes then optimised int3. Now if you want to do markup for awkward tracepoints for kprobe use then the same rules seem to apply - jprobes and the int3 optimisation mean you don't need to go shoving nops in code paths that are used all the time. Alan - 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/