linux-kernel - Re: [PATCHv2 00/25] perf tool: Add support for multiple data file storage

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Date:	Mon, 9 Sep 2013 13:36:41 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCHv2 00/25] perf tool: Add support for multiple data file
 storage

On Mon, Sep 09, 2013 at 01:17:49PM +0200, Peter Zijlstra wrote:
> On Sun, Sep 01, 2013 at 12:36:11PM +0200, Jiri Olsa wrote:
> > hi,
> > sending the support for multiple file storage. Initial
> > RFC is here:
> > http://marc.info/?l=linux-kernel&m=137408381902423&w=2
> > 
> > v2 changes:
> >   - reworked perf mmap size setup to be able to get
> >     the mmap size value easily later
> >   - added perf.data read/write test for v2 and v3
> >     for both endianity
> >   - added record '-M time' support
> 
> So this 0/n post seems to have forgotten to list the rationale for doing
> all this.. 

here it is:

This patchset is actually doing 3 essential things:
  1) adds new perf data format version (v3)
  2) adds class/object to handle perf data file
  3) adds record '-M size' option

ad 1) Along the way I realized it'd be much easier to have the
      format simplified. I ended up with just 'DATA' and 'FEATURES'
      sections making the file format more generic.

      The easier/generic format will be for example useful for the
      cpu hotplug notification (and maybe even for ftrace data files
      features?)

      The version 2 should be still readable by perf, while it
      produces data in version 3 from this patchset onwards.

ad 2) I needed to unify perf data file handling to make the -M
      implementation clear.

> 
> The only reason I wanted this is so that each thread can write its own
> data. The current one file thing is an immense bottle-neck for big
> machines.
> 

I haven't considered the thread based storage yet, but I
think having the simplified format and centralized file
handling will only help.

jirka
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