linux-kernel - Re: [GIT PULL 00/37] perf/core improvements and fixes

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Date:	Wed, 27 May 2015 09:35:32 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
	David Ahern <dsahern@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Josef Bacik <jbacik@...com>,
	kernel-team@...com, Luigi Semenzato <semenzato@...omium.org>,
	Martin Liska <mliska@...e.cz>,
	Namhyung Kim <namhyung@...nel.org>,
	"Nam T . Nguyen" <namnguyen@...omium.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Simon Que <sque@...omium.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [GIT PULL 00/37] perf/core improvements and fixes

Em Wed, May 27, 2015 at 09:38:47AM +0200, Ingo Molnar escreveu:
> * Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > New features:

> > - Intel PT support, should be complete now and possible to test it with what we
> >   already have in the kernel, go, test it and report problems on lkml, I'm sure
> >   Adrian will chime in if something doesn't work as documented. (Adrian Hunter)
 
> So how can people follow your request?

First by having access to a machine with these hardware features, which,
for one, I have no easy access to right now :-\
 
> The changelogs are minimal, sometimes they only say:

They improved over time, over the many resubmits Adrian made, so some
progress was made on this front.
 
>   From 7a84d68975f34c912cb6ec8adb3c1869c15b5c36 Mon Sep 17 00:00:00 2001
>   From: Adrian Hunter <adrian.hunter@...el.com>
>   Date: Fri, 22 May 2015 14:54:04 +0300
>   Subject: [PATCH] perf tools: Add Intel PT support

>   Add support for Intel Processor Trace.
 
> there's almost zero comments added by these commits.

I shouldn't have let some pass, granted.
 
> This commit:
> 
>   928541b6f51f perf tools: Take Intel PT into use
> 
> adds 'some documentation' under ./Documentation/intel-pt.txt, but that text 
> doesn't actually give any high level description, it doesn't give _any_ way for a 
> user to discover Intel PT support on his own - unless he already knows it, which 
> is kind of circular.

> It doesn't describe which CPUs support Intel PT, what it is, how are people 
> supposed to use it, what the high level capabilities and limitations are, etc. 
> etc.
 
> So this stuff is user and developer hostile at the moment. We can push this 
> towards Linus only if this becomes _much_ more user and developer friendly. Near 
> zero documentation and near zero comments in the code don't cut it really.

Adrian, can you try to address this further, please?

Something like a handholding session, so that we don't have to dig thru
all the csets or patch series cover letters, telling:

1. What hardware one has to have to be able to test it

2. First command to use

3. What will be generated, how much space (a lot?) it will use on the
   perf.data file, etc.

5. What commands have to be used on this perf.data file and what to
   expect from it.

I.e. a HOWTO that starts with a as short as possible description on how
 to use it for the very first time, for people never exposed to Intel PT
but that can benefit from using it.

Ingo, so I'll move these csets to a separate branch from where I can
work with Adrian and others to then try again to resubmit, but only on a
branch exclusively for this.

Will resubmit a perf/core branch with the remaining bits soon.

- Arnaldo
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