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

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Date:	Mon, 9 Sep 2013 18:06:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCHv2 00/25] perf tool: Add support for multiple data file
 storage


* David Ahern <dsahern@...il.com> wrote:

> On 9/9/13 7:03 AM, Jiri Olsa wrote:
> >my usage currently is to having this running during the day:
> >(well whenever I remember to run it.. ;-) )
> >
> >   [jolsa@...va perf]$ sudo ./perf record -g -M 1m -a
> >
> >and checking report when the system or app get stuck
> >
> >with multiple files I can just easily (or automaticaly)
> >remove old ones without restarting session
> 
> Aren't you losing potentially important events by doing that -- FORK, 
> COMM, MMAP?

I suspect these could/should be tracked and emitted fully (in bulk) when a 
new data file is opened, so that each partial data file is fully 
consistent?

> I have a flight recorder style command that address this problem 
> (long-running/daemons) by processing task events and then stashing the 
> sample events on a time-ordered list with chopping to maintain the time 
> window.

Could this be used to emit currently relevant task context?

Btw., I also think it would be useful to have kernel support for that - 
the 'collections' stuff I talked about a good while ago: the kernel would 
work with user-space to iterate over all MMAPs and all running COMMs at 
the opening of a tracing session.

That way we could avoid racy access to /proc, we could make sure that all 
information that is emitted by FORK/COMM/MMAP is also emitted for the 
'bulk' data, etc.

Thanks,

	Ingo
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