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

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Date:	Mon, 09 Sep 2013 08:03:21 -0700
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	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

On 9/9/13 7:31 AM, Jiri Olsa wrote:
> On Mon, Sep 09, 2013 at 07:11:11AM -0700, David Ahern 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?
>
> those are synthesized for each file via synthesize_record
> function, see:
>
> [PATCH 19/25] perf tools: Move synthesizing into single function

Ok. haven't had time to look through your 2 large patch sets.

Seems like a lot of repetitive work on a loaded system. The overhead of 
the task events will dominate compared to the samples.

>
>>
>> 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.
>
> so far I noticed there could be race among EXIT and remaining
> SAMPLE events on another CPU mmap than EXIT event.. ending up
> with EXIT being stored in the old file, while SAMPLEs will get
> to the new one
>
> I was thinking about some 'perf daemon' so I dont need to run that
> manually.. seems similar to what you did

Right now I focus on scheduling events. This latest version of it can be 
easily recycled for other use cases. Some work would be needed to dump 
events to a file versus dumping processed information.

I am in San Jose this week. Not sure if I will have time to finish it to 
a point of pushing out patches, but maybe I can push to github in the 
next couple of days.

David
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