linux-kernel - Re: [RFC/PATCH 03/38] perf tools: Move auxtrace_mmap field to struct perf

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Date:	Wed, 7 Oct 2015 18:06:12 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC/PATCH 03/38] perf tools: Move auxtrace_mmap field to struct perf_evlist

Hi Adrian,

On Tue, Oct 6, 2015 at 6:26 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 06/10/15 12:03, Namhyung Kim wrote:
>> Hi Adrian,
>>
>> On Mon, Oct 5, 2015 at 8:29 PM, Adrian Hunter <adrian.hunter@...el.com> wrote:
>>> On 02/10/15 21:45, Arnaldo Carvalho de Melo wrote:
>>>> Em Fri, Oct 02, 2015 at 02:18:44PM +0900, Namhyung Kim escreveu:
>>>>> Since it's gonna share struct mmap with dummy tracking evsel to track
>>>>> meta events only, let's move auxtrace out of struct perf_mmap.
>>>> Is this moving around _strictly_ needed?
>>>
>>> Also, what if you wanted to capture AUX data and tracking together.
>>
>> Hmm.. I don't know what's the problem.  It should be orthogonal and
>> support doing that together IMHO.  Maybe I'm missing something about
>> the aux data processing and Intel PT.  I'll take a look at it..
>>
>
> It is only orthogonal if you assume we will never want to support parallel
> processing with Intel PT.

We'll definitely want it. :)

>
> The only change that needs to be made is not to assume there is only 1
> tracking event.

IIUC Intel PT (and BTS?) needs maximum 2 dummy events - one is to
track task/mmap and another is to track context switches.  The latter
is basically a light-weight version of the sched_switch event, right?

For parallel processing, each cpu needs to keep current thread to
synthesize events from auxtrace data.  So if it processed the switch
events before processing samples, it'd need to build long lists of
current thread per cpu.  IMHO it'd be better to process the switch
events with samples using multi-thread rather than processing them
prior to samples.

So how about this?  It'd use *always* 2 dummy (or 1 dummy + 1
sched_switch) events.  The tracking dummy events would be recorded on
the tracking mmaps and switch (dummy) event would be recorded on the
main mmaps.  This way we can parallelize the auxtrace processing
without the list of current thread IMHO.

Do I miss something?

>
> IMHO there could be separate mmap_params also, which would allow for
> different mmap sizes for the tracking and main mmaps.

Currently, the tracking mmap size is fixed at an arbitrary size
(128KiB) regardless of the main mmaps.  I can add an option to change
the tracking mmap size too.

Thanks,
Namhyung
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