From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753740AbXGGR40 (ORCPT ); Sat, 7 Jul 2007 13:56:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752496AbXGGR4U (ORCPT ); Sat, 7 Jul 2007 13:56:20 -0400 Received: from mx1.redhat.com ([66.187.233.31]:33554 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752439AbXGGR4U (ORCPT ); Sat, 7 Jul 2007 13:56:20 -0400 Date: Sat, 7 Jul 2007 13:55:03 -0400 From: "Frank Ch. Eigler" To: Adrian Bunk Cc: Dave Jones , Chuck Ebbert , Andi Kleen , Andrew Morton , Mathieu Desnoyers , Alexey Dobriyan , linux-kernel@vger.kernel.org Subject: Re: [patch 10/10] Scheduler profiling - Use immediate values Message-ID: <20070707175503.GI24475@redhat.com> References: <20070703181151.GB5800@martell.zuzino.mipt.ru> <20070703185748.GA4047@Krystal> <20070705132120.8edbc1f3.akpm@linux-foundation.org> <468EBEB2.4070605@redhat.com> <20070706232843.GT3492@stusta.de> <20070706233827.GC13125@redhat.com> <20070707001008.GV3492@stusta.de> <20070707170157.GH3492@stusta.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070707170157.GH3492@stusta.de> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, Adrian - On Sat, Jul 07, 2007 at 07:01:57PM +0200, Adrian Bunk wrote: > [...] > > Things are not so simple. One might not know that one has a > > performance problem until one tries some analysis tools. Rebooting > > into different kernels just to investigate does not work generally [...] > > I'm not getting this: > > You'll only start looking into an analysis tool if you have a > performance problem, IOW if you are not satisfied with the > performance. There may be people whose jobs entail continually suspecting performance problems. Or one may run instrumentation code on a long-term basis specifically to locate performance spikes. > And the debug code will not have been tested on this machine no matter > whether it's enabled through a compile option or at runtime. There is a big difference in favour of the former. The additional instrumentation code may be small enough to inspect carefully. The rest of the kernel would be unaffected. > [...] If you might be able to get a big part of tracing and other > debug code enabled with a performance penalty of a few percent of > _kernel_ performance, then you might get much debugging aid without > any effective impact on application performance. Agreed. - FChE