Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751113Ab0KQXWk (ORCPT ); Wed, 17 Nov 2010 18:22:40 -0500 Received: from smtp-out.google.com ([74.125.121.35]:54191 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750698Ab0KQXWj convert rfc822-to-8bit (ORCPT ); Wed, 17 Nov 2010 18:22:39 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=wrbrn0nws+YR5lVQRAH8Rm/nBDDSKOO7FrswIA6qIfhWLUAXQoFNfFTNexCEMLM0hs HjQtjK2D4g4AKyXZqJmA== MIME-Version: 1.0 In-Reply-To: <1290034589.4ce45d9d7be28@www.imp.polymtl.ca> References: <1290029498.4ce449ba1679d@www.imp.polymtl.ca> <1290030106.30543.74.camel@gandalf.stny.rr.com> <1290034589.4ce45d9d7be28@www.imp.polymtl.ca> From: David Sharp Date: Wed, 17 Nov 2010 15:22:15 -0800 Message-ID: Subject: Re: Benchmarks of kernel tracing options 2 (ftrace, lttng and perf) To: Douglas Santos Cc: Steven Rostedt , "linux-kernel@vger.kernel.org" , "ltt-dev@lists.casi.polymtl.ca" , Mathieu Desnoyers , Ingo Molnar , Andrew Morton , Michael Rubin Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1794 Lines: 52 On Wed, Nov 17, 2010 at 2:56 PM, Douglas Santos wrote: > Quoting Steven Rostedt : >> On Wed, 2010-11-17 at 16:31 -0500, Douglas Santos wrote: >> > Hi all, >> > >> > This is a response to a benchmark, submitted a few weeks ago, comparing >> kernel >> > tracing options. >> > http://lkml.org/lkml/2010/10/28/422 >> > >> > We followed the methodology described in the link bellow, >> > but using the shellscripts posted there to reproduce autotest scripts. >> > http://lkml.org/lkml/2010/10/28/261 >> > >> > We disabled the extra syscall tracing on lttng, for a fair comparison. >> > http://lkml.org/lkml/2010/10/28/290 >> > >> > Average results with tracing "on": >> > >> > lttng:  220 ns >> > ftrace: 260 ns >> >> Heh, so ftrace got worse with the new kernel? Steve, can you explain how you're drawing that conclusion? Did Douglas run this benchmark before on a previous kernel (I didn't see it if so)? - You can't directly compare to my results because of different hardware. - The methodology for lttng is different (syscall tracing was removed). - My results were also on 2.6.36 > The previous bench was doing tracing "on" minus "off" > average results. They also used autotest scripts, not sure if > it does exactly the same thing. I think the subtraction is important, or it is at least important to see what the "off" result is as a baseline of comparison. Otherwise, a huge portion of the measurement is the cost of making the syscall itself. > > I'll check if we missed something. > > > -- 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/