From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 27476 invoked by alias); 10 Sep 2011 00:14:17 -0000 Received: (qmail 27447 invoked by uid 22791); 10 Sep 2011 00:14:14 -0000 X-SWARE-Spam-Status: No, hits=-6.5 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD,SPF_HELO_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Sat, 10 Sep 2011 00:13:53 +0000 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p8A0DpWt008457 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 9 Sep 2011 20:13:51 -0400 Received: from fche.csb (vpn-9-29.rdu.redhat.com [10.11.9.29]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id p8A0DoQU029173; Fri, 9 Sep 2011 20:13:51 -0400 Received: by fche.csb (Postfix, from userid 2569) id 786B35814D; Fri, 9 Sep 2011 20:13:50 -0400 (EDT) Date: Sat, 10 Sep 2011 00:14:00 -0000 From: "Frank Ch. Eigler" To: ydev Cc: systemtap@sourceware.org Subject: Re: Performance Impact of Systemtap Message-ID: <20110910001350.GB1560@redhat.com> References: <20110910001315.GA1560@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110910001315.GA1560@redhat.com> User-Agent: Mutt/1.4.2.2i Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2011-q3/txt/msg00312.txt.bz2 On Wed, Sep 07, 2011 at 08:42:23PM -0600, ydev wrote: > Thank you Frank. I'm very new to SystemTap so could you please > tell me what is the -DSTP_ALIBI mode run. -DSTP_ALIBI compiles out the probe handlers from the systemtap module, leaving only the parts that hook into the kernel, and just keep hit counts/time. So it's as if the probe handlers were all { } empty. > [...] I started systemtap in flight mode and triggered many > reads/write and used the 'time' command to measure how long it takes > to execute cat. OK. > I did this without systemtap running in the background. The figures > were almost the same. I'm not sure if using 'time' command gives me > accurate results. Overall elapsed times should be accurate with /bin/time. Instrumenting relatively few & slow calls like disk I/O should indeed have negligible overhead when instrumented with systemtap. - FChE