From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757120Ab3KOLUj (ORCPT ); Fri, 15 Nov 2013 06:20:39 -0500 Received: from mga09.intel.com ([134.134.136.24]:22701 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752943Ab3KOLUc (ORCPT ); Fri, 15 Nov 2013 06:20:32 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,535,1378882800"; d="scan'208";a="435748402" Message-ID: <52860529.50200@intel.com> Date: Fri, 15 Nov 2013 13:27:37 +0200 From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Ingo Molnar CC: Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, David Ahern , Frederic Weisbecker , Ingo Molnar , Jiri Olsa , Mike Galbraith , Namhyung Kim , Paul Mackerras , Peter Zijlstra , Stephane Eranian , Arnaldo Carvalho de Melo , Namhyung Kim Subject: Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps References: <1384460715-23198-1-git-send-email-acme@infradead.org> <1384460715-23198-11-git-send-email-acme@infradead.org> <20131115060643.GA9237@gmail.com> <5285FECE.7020802@intel.com> <20131115111032.GA18647@gmail.com> In-Reply-To: <20131115111032.GA18647@gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/11/13 13:10, Ingo Molnar wrote: > > * Adrian Hunter wrote: > >>> And I also raised why this shouldn't be the default event tracing >>> method instead of a weird config option. Per-cpu tracing is cache >>> compact, it is easier to size properly and in general it is pretty >>> easy to think about. (It also has less of the TSC timestamp >>> ordering problems as per thread tracing, at least in theory.) >>> >>> Is there something that makes per cpu tracing undesirable as the >>> default? >> >> One reason is to avoid changing the meaning of existing options. > > Well, the way the tracing buffers are set up is a mostly tool internal > matter so in that sense it should be just fine to change the default > behavior - as long as output remains unchanged (which it should). > > Or is there any material change in behavior somewhere? Inheritance is enabled automatically with per-cpu mmaps, although that is one of the reasons people want per-cpu mmaps. > >> To flip it around, ignore the patches above and apply: > >> Subject: [PATCH] perf record: Make per-cpu mmaps the default. > > Yay! > >> +--per-thread:: >> +Use per-thread mmaps. By default per-cpu mmaps are created. This option >> +overrides that and uses per-thread mmaps. A side-effect of that is that >> +inheritance is automatically disabled. --per-thread is ignored with a warning >> +if combined with -a or -C options. > > I think this is the natural thing to do, --per-thread is the 'somewhat > weird' option that cannot be used in all modes. > > Acked-by: Ingo Molnar > > :-) > > Thanks, > > Ingo > >