From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758466Ab3KOLKq (ORCPT <rfc822;w@1wt.eu>);
	Fri, 15 Nov 2013 06:10:46 -0500
Received: from mail-ee0-f43.google.com ([74.125.83.43]:49367 "EHLO
	mail-ee0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1756980Ab3KOLKj (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 15 Nov 2013 06:10:39 -0500
Date: Fri, 15 Nov 2013 12:10:32 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>,
        linux-kernel@vger.kernel.org, David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
        Mike Galbraith <efault@gmx.de>, Namhyung Kim <namhyung@gmail.com>,
        Paul Mackerras <paulus@samba.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Stephane Eranian <eranian@google.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 10/10] perf record: Add an option to force per-cpu mmaps
Message-ID: <20131115111032.GA18647@gmail.com>
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>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5285FECE.7020802@intel.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Adrian Hunter <adrian.hunter@intel.com> 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?

> 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 <mingo@kernel.org>

:-)

Thanks,

	Ingo