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 S1754706AbaIPR6l (ORCPT <rfc822;w@1wt.eu>);
	Tue, 16 Sep 2014 13:58:41 -0400
Received: from mail-wi0-f170.google.com ([209.85.212.170]:45978 "EHLO
	mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751013AbaIPR6j (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 16 Sep 2014 13:58:39 -0400
Date: Tue, 16 Sep 2014 19:58:34 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Pawel Moll <pawel.moll@arm.com>
Cc: David Ahern <dsahern@gmail.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Richard Cochran <richardcochran@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Paul Mackerras <paulus@samba.org>,
        John Stultz <john.stultz@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: Re: [RFC 2/2] perf: Marker software event and ioctl
Message-ID: <20140916175834.GA13970@gmail.com>
References: <1410522513-1045-1-git-send-email-pawel.moll@arm.com>
 <1410522513-1045-3-git-send-email-pawel.moll@arm.com>
 <54132F63.1010401@gmail.com>
 <20140912204444.GA11199@kernel.org>
 <5415B790.5010607@gmail.com>
 <20140916074421.GA21295@gmail.com>
 <1410885463.12376.24.camel@hornet>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1410885463.12376.24.camel@hornet>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Pawel Moll <pawel.moll@arm.com> wrote:

> On Tue, 2014-09-16 at 08:44 +0100, Ingo Molnar wrote:
> > I think adding an ioctl to inject user-provided data into the 
> > event stream is sensible, as long as there's a separate 'user 
> > generated data' event for it, etc.
> > 
> > The main usecase I could see would be to introduce a 
> > perf_printf() variant, supported by 'perf trace' by default, to 
> > add various tracable printouts to apps.
> > 
> > Timestamps generated by apps would be another usecase. It would 
> > probably be wise to add a 32-bit (or 64-bit) message type ID, 
> > plus a length field, with a message type registry somewhere in 
> > tools/perf/ (and reference implementation for each new subtype), 
> > to keep things organized yet flexible going forward.
> 
> Right, so this is pretty much what I got talking to Arnaldo...
> 
> >       { u64 type; /* 0 means zero-terminated string in data */
> >         u32 size;
> >         char data[size]; } && PERF_SAMPLE_MARKER
> 
> ... with one type - 0 - defined as a "universal" string (so any 
> possible tool knows what to do about it), the rest being left 
> to userspace (this "registry" you mention).
> 
> Before I proceed any further, is the term "marker" acceptable? 
> Maybe a "printf" instead? Or a "log"? As we know naming is 
> often single most discussed subject when it comes to new things 
> in the kernel ;-)

Well, it's a user-space generated trace/event entry, so lets call 
it that?

Thanks,

	Ingo