From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1757216AbZJPHnU@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1757216AbZJPHnU (ORCPT <rfc822;w@1wt.eu>);
	Fri, 16 Oct 2009 03:43:20 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757124AbZJPHnT
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Fri, 16 Oct 2009 03:43:19 -0400
Received: from mx3.mail.elte.hu ([157.181.1.138]:45735 "EHLO mx3.mail.elte.hu"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1757053AbZJPHnT (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 16 Oct 2009 03:43:19 -0400
Date: Fri, 16 Oct 2009 09:42:22 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Mike Galbraith <efault@gmx.de>, Paul Mackerras <paulus@samba.org>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] perf tools: Add a new generic section in perf.data
Message-ID: <20091016074222.GD30019@elte.hu>
References: <1255641017-13958-1-git-send-email-fweisbec@gmail.com> <20091016071046.GD20388@elte.hu> <20091016073337.GA5069@nowhere>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20091016073337.GA5069@nowhere>
User-Agent: Mutt/1.5.18 (2008-05-17)
X-ELTE-SpamScore: 0.0
X-ELTE-SpamLevel: 
X-ELTE-SpamCheck: no
X-ELTE-SpamVersion: ELTE 2.0 
X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=none autolearn=no SpamAssassin version=3.2.5
	_SUMMARY_
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Fri, Oct 16, 2009 at 09:10:46AM +0200, Ingo Molnar wrote:
> > 
> > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > 
> > > +/*
> > > + * Version 0: contains trace_info section only
> > > + */
> > > +struct perf_file_additionals {
> > > +	u64				version;
> > > +	struct perf_file_section	trace_info;
> > > +};
> > 
> > i dont disagree with the change - but it would be even nicer to simply 
> > define a features bitmask, instead of a flat version - and add the 
> > trace_info section as a feature.
> > 
> > That way it's all a lot more manageable: we dont know about versions per 
> > se, we know about features. Individual features could be developed (and 
> > backported) in a distributed way - without having to worry about a flat 
> > version model.
> > 
> > So i'd suggest something like a bitmask in the perf.data file header:
> > 
> > 	DECLARE_BITMAP(features, 256);
> > 
> > Plus every perf version knows about the features it supports:
> > 
> > 	DECLARE_BITMAP(features_supported, 256);
> > 
> > The compatibility rule is: perf only touches attributes that belong to 
> > features it knows about.
> > 
> > 	Ingo
> 
> 
> Yeah, I've thought about that too but feared about the limitation of 
> bitweight(u64), although it's probably enough, we never know. That 
> said I can take a bunch of four u64 to draw this bitmap and 256 
> features is enough.
> 
> Indeed that's way much better as a bitmap. Will do that instead.

Yeah, but please reuse linux/bitmap.h instead of some open-coded array 
of 4x u64's.

	Ingo