linux-kernel - Re: [PATCH V2 0/5] event synthesization multithreading for perf record

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Date:   Wed, 18 Oct 2017 19:04:04 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     kan.liang@...el.com
Cc:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
        peterz@...radead.org, jolsa@...nel.org, wangnan0@...wei.com,
        hekuang@...wei.com, namhyung@...nel.org,
        alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
        ak@...ux.intel.com
Subject: Re: [PATCH V2 0/5] event synthesization multithreading for perf
 record


* kan.liang@...el.com <kan.liang@...el.com> wrote:

> From: Kan Liang <Kan.liang@...el.com>
> 
> The event synthesization multithreading is introduced in
> ("perf top optimization") https://lkml.org/lkml/2017/9/29/269
> But it was not enabled for perf record. Because the process function
> process_synthesized_event was not multithreading friendly.
> 
> The patch series temporarily stores the process result in per-thread file,
> which make the processing in parallel. Then it dumps the file one by one to
> the perf.data at the end of event synthesization.
> 
> The source code is also available at
> https://github.com/kliang2/perf.git perf_record_opt
> 
> Usually, the event synthesization only happens once on either start or end.
> With the snapshotting code, we synthesize events multiple times, once per
> each new perf.data file. Both of the cases are verified.
> 
> Here are the latency test result on Knights Mill and Skylake server
> 
> The workload is to compile Linux kernel as below
> "sudo nice make -j$(grep -c '^processor' /proc/cpuinfo)"
> Then, "sudo perf record -e cycles -a -- sleep 1"
> 
> The latency is the time cost of __machine__synthesize_threads or
> its multithreading replacement, record__multithread_synthesize.
> 
> - Latency on Knights Mill (272 CPUs)
> 
> Original(s)     With patch(s)   Speedup
> 12.74           5.54            2.3X
> 
> - Latency on Skylake server (192 CPUs)
> 
> Original(s)     With patch(s)   Speedup
> 0.36            0.25            1.47X

Btw., just as an interesting experiment, could you try to measure how it performs 
to create just the per-CPU files, and *not* dump them into a single file?

I.e. how much faster will it get if the serialization at the end is avoided?

Of course nothing can read such per-CPU files yet, so this is just for scalability 
measurement.

Thanks,

	Ingo