From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755481AbcBCL3d (ORCPT ); Wed, 3 Feb 2016 06:29:33 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36799 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752839AbcBCL2x (ORCPT ); Wed, 3 Feb 2016 06:28:53 -0500 Date: Wed, 3 Feb 2016 12:28:49 +0100 From: Ingo Molnar To: Mel Gorman Cc: Peter Zijlstra , Matt Fleming , Mike Galbraith , Srikar Dronamraju , LKML Subject: Re: [PATCH 1/1] sched: Make schedstats a runtime tunable that is disabled by default v4 Message-ID: <20160203112849.GB27850@gmail.com> References: <1454497668-22297-1-git-send-email-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1454497668-22297-1-git-send-email-mgorman@techsingularity.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mel Gorman wrote: > Changelog since v3 > o Force enable stats during profiling and latencytop > > Changelog since V2 > o Print stats that are not related to schedstat > o Reintroduce a static inline for update_stats_dequeue > > Changelog since V1 > o Introduce schedstat_enabled and address Ingo's feedback > o More schedstat-only paths eliminated, particularly ttwu_stat > > schedstats is very useful during debugging and performance tuning but it > incurs overhead. As such, even though it can be disabled at build time, > it is often enabled as the information is useful. This patch adds a > kernel command-line and sysctl tunable to enable or disable schedstats on > demand. It is disabled by default as someone who knows they need it can > also learn to enable it when necessary. > > The benefits are workload-dependent but when it gets down to it, the > difference will be whether cache misses are incurred updating the shared > stats or not. [...] Hm, which shared stats are those? I think we should really fix those as well: those shared stats should be percpu collected as well, with no extra cache misses in any scheduler fast path. Thanks, Ingo