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Date: Mon, 9 Sep 2013 18:06:08 +0200
From: Ingo Molnar <mingo@kernel.org>
To: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org,
        Corey Ashford <cjashfor@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
        Namhyung Kim <namhyung@kernel.org>, Paul Mackerras <paulus@samba.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCHv2 00/25] perf tool: Add support for multiple data file
 storage
Message-ID: <20130909160608.GB25555@gmail.com>
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* David Ahern <dsahern@gmail.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@krava 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