From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 82378 invoked by alias); 12 Dec 2016 17:43:54 -0000 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 Received: (qmail 82370 invoked by uid 89); 12 Dec 2016 17:43:53 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.5 required=5.0 tests=BAYES_50,KAM_ASCII_DIVIDERS,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=refresh, cody, Cody, D*arch X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 12 Dec 2016 17:43:52 +0000 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 67DCCC05AA56; Mon, 12 Dec 2016 17:43:51 +0000 (UTC) Received: from fche.csb (vpn-62-98.rdu2.redhat.com [10.10.62.98]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id uBCHhopI020380; Mon, 12 Dec 2016 12:43:51 -0500 Received: by fche.csb (Postfix, from userid 2569) id 7B150589BA; Mon, 12 Dec 2016 12:43:50 -0500 (EST) From: fche@redhat.com (Frank Ch. Eigler) To: Aubrey Li , Cody Santing Cc: systemtap@sourceware.org Subject: Re: Fwd: kernel function probe overhead References: Date: Mon, 12 Dec 2016 17:43:00 -0000 In-Reply-To: (Cody Santing's message of "Mon, 12 Dec 2016 12:07:23 -0500") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2016-q4/txt/msg00116.txt.bz2 aubreylee wrote; > Thanks Cody. > Here is what I got: > > ============================================================ > $ sudo stap -t test.stp > ----------------------------------------- > [...] > kernel.function("arch_cpu_idle_enter@arch/x86/kernel/process.c:277").call, > (./test.stp:14:1), hits: 2962, cycles: > >>400min/30951avg/233043max, variance: 824817112, from: kernel.function("arch_cpu_idle_enter@arch/x86/kernel/process.c:277").call > > May I know what does variance value mean here? This is normal statistical variance, i.e., the square of the standard deviation. That means that the bulk of the probe execution times were within sqrt(824817712)=28719 cycles from the mean, if the distribution were roughly normal. > ----- refresh report: >>'__global_t_start' lock contention occurred 2853 times > > Would it be nice to report time cost of lock contention? That would be roughly #-contentions * TRYLOCKDELAY (default 10us), so about 29 ms. > Anyway, instead of reporting lock contention, it would be nice if we > can reduce it, :) Sure, but a good first step is to know the magnitude of the problem. - FChE