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

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Date:	Wed, 27 May 2015 15:40:11 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
CC:	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

On 27/05/15 15:35, Arnaldo Carvalho de Melo wrote:
> 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?

Yes, I will mainly expand the information in
tools/perf/Documentation/intel-pt.txt unless you have any other ideas.

> 
> 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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