Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751824AbWIRQXx (ORCPT ); Mon, 18 Sep 2006 12:23:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751825AbWIRQXx (ORCPT ); Mon, 18 Sep 2006 12:23:53 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:20096 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S1751824AbWIRQXw (ORCPT ); Mon, 18 Sep 2006 12:23:52 -0400 Date: Mon, 18 Sep 2006 18:15:11 +0200 From: Ingo Molnar To: Alan Cox 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" Subject: Re: tracepoint maintainance models Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1158596341.6069.130.camel@localhost.localdomain> 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: 1289 Lines: 27 * Alan Cox wrote: > Ar Llu, 2006-09-18 am 17:22 +0200, ysgrifennodd Ingo Molnar: > > yeah - but i think to make it easier for SystemTap to insert a > > low-overhead probe there needs to be a 5-byte NOP inserted. There wont > > be any function call or condition at that place. At most there will be > > some minimal impact on the way gcc compiles the code in that function, > > And more L1 misses. It seems that this problem should be solved by > jprobes and your int3 optimisation work. 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 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. In general there is no guarantee from gcc that any probe can be inserted into a function (djprobes and int3 optimization nonwithstanding) and this is a real practical problem for SystemTap. Frank can attest to that. 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/