Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750944AbWIRP4K (ORCPT ); Mon, 18 Sep 2006 11:56:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751798AbWIRP4J (ORCPT ); Mon, 18 Sep 2006 11:56:09 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:8682 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1750928AbWIRP4I (ORCPT ); Mon, 18 Sep 2006 11:56:08 -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: <20060918152230.GA12631@elte.hu> References: <450D182B.9060300@opersys.com> <20060917112128.GA3170@localhost.usen.ad.jp> <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> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Mon, 18 Sep 2006 17:19:01 +0100 Message-Id: <1158596341.6069.130.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: 1326 Lines: 27 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. > SystemTap. For example at the point of the probe gcc might already have > destroyed a register-passed function parameter. So its L1 misses more register reloads and the like. Sounds more and more like wasted clock cycles for debug. Most of these watchpoints will run billions of times a day on millions of machines none of whom are using any debugging. You are optimising the corner case (in the extreme in fact). Its one thing to dump trace helper data into the kernel, its another when we all get to pay for it all the time when we don't need to (or we compile it out at which point it offers nothing anyway). 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/