From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757735AbcAYRHW (ORCPT ); Mon, 25 Jan 2016 12:07:22 -0500 Received: from outbound-smtp08.blacknight.com ([46.22.139.13]:34951 "EHLO outbound-smtp08.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757701AbcAYRHU (ORCPT ); Mon, 25 Jan 2016 12:07:20 -0500 Date: Mon, 25 Jan 2016 17:07:16 +0000 From: Mel Gorman To: Ingo Molnar Cc: Peter Zijlstra , Matt Fleming , Mike Galbraith , LKML Subject: Re: [PATCH] sched: Make schedstats a runtime tunable that is disabled by default Message-ID: <20160125170716.GI3162@techsingularity.net> References: <1453716331-21029-1-git-send-email-mgorman@techsingularity.net> <20160125112606.GV6357@twins.programming.kicks-ass.net> <20160125133944.GE3162@techsingularity.net> <20160125145944.GZ6357@twins.programming.kicks-ass.net> <20160125154635.GB4031@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20160125154635.GB4031@gmail.com> 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 On Mon, Jan 25, 2016 at 04:46:35PM +0100, Ingo Molnar wrote: > > Of course, it'll be our luck that tracking the data for these > > tracepoints is the most expensive part of schedstats ... > > > > Ingo? > > IIRC it needed only a small subset of schedstats to make those tracepoints work. > > We already have too much overhead in the scheduler as-is - and the extra cache > footprint does not even show on the typically cache-rich enterprise CPUs most of > the scalability testing goes on. > > My minimum requirement for such runtime enablement would be to make it entirely > static-branch patched and triggered at the call sites as well - not hidden inside > schedstat functions. > As it is, it's static-branch patched but I'm struggling to see why they cannot be hidden in the schedstat_* functions which are just preprocessor macros. The checks could be put in the callsites but it's a lot of updates and I don't think the end result would be very nice to read. -- Mel Gorman SUSE Labs