linux-kernel - Re: [PATCHv2 00/18] perf tools: Factor ordered samples queue

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Date:	Wed, 18 Jun 2014 13:44:46 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCHv2 00/18] perf tools: Factor ordered samples queue

On 6/18/14, 8:58 AM, Jiri Olsa wrote:
> hi,
> this patchset factors session's ordered samples queue,
> and allows to limit the size of this queue.
>
> v2 changes:
>    - several small changes for review comments (Namhyung)
>
>
> The report command queues events till any of following
> conditions is reached:
>    - PERF_RECORD_FINISHED_ROUND event is processed
>    - end of the file is reached
>
> Any of above conditions will force the queue to flush some
> events while keeping all allocated memory for next events.
>
> If PERF_RECORD_FINISHED_ROUND is missing the queue will
> allocate memory for every single event in the perf.data.
> This could lead to enormous memory consuption and speed
> degradation of report command for huge perf.data files.
>
> With the quue allocation limit of 100 MB, I've got around
> 15% speedup on reporting of ~10GB perf.data file.
>
> current code:
>   Performance counter stats for './perf.old report --stdio -i perf-test.data' (3 runs):
>
>     621,685,704,665      cycles                    ( +-  0.52% )
>     873,397,467,969      instructions              ( +-  0.00% )
>
>       286.133268732 seconds time elapsed           ( +-  1.13% )
>
> with patches:
>   Performance counter stats for './perf report --stdio -i perf-test.data' (3 runs):
>
>     603,933,987,185      cycles                    ( +-  0.45% )
>     869,139,445,070      instructions              ( +-  0.00% )
>
>       245.337510637 seconds time elapsed           ( +-  0.49% )
>
>
> The speed up seems to be mainly in less cycles spent in servicing
> page faults:
>
> current code:
>       4.44%     0.01%  perf.old  [kernel.kallsyms]   [k] page_fault
>
> with patches:
>       1.45%     0.00%      perf  [kernel.kallsyms]   [k] page_fault
>
> current code (faults event):
>           6,643,807      faults                    ( +-  0.36% )
>
> with patches (faults event):
>           2,214,756      faults                    ( +-  3.03% )
>
>
> Also now we have one of our big memory spender under control
> and the ordered events queue code is put in separated object
> with clear interface ready to be used by another command
> like script.
>
> Also reachable in here:
>    git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
>    perf/core_ordered_events
>

I've skimmed through the patches. What happens if you are in the middle 
of a round and the max queue size is reached?

I need to find some time for a detailed review, and to run through some 
stress case scenarios. e.g., a couple that come to mind
perf sched record -- perf bench sched pipe
perf kvm record while booting a nested VM which causes a lot of VMEXITs

David

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