linux-kernel - Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during per-process profiling of STREAM benchmark on Intel Xeon Phi

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Date:   Mon, 19 Jun 2017 17:09:00 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/n] perf/core: addressing 4x slowdown during
 per-process profiling of STREAM benchmark on Intel Xeon Phi

On 19.06.2017 16:38, Mark Rutland wrote:
> On Mon, Jun 19, 2017 at 01:46:39PM +0100, Mark Rutland wrote:
>> On Fri, Jun 16, 2017 at 05:22:29PM +0300, Alexey Budankov wrote:
>>> On 16.06.2017 17:08, Alexey Budankov wrote:
>>>> On 16.06.2017 12:09, Mark Rutland wrote:
>>>>> There's a --per-thread option to ask perf record to not duplicate the
>>>>> event per-cpu.
>>>>>
>>>>> If you use that, what amount of slowdown do you see?
>>>
>>> After applying all three patches:
>>>
>>> - system-wide collection:
>>>
>>> [ perf record: Woken up 1 times to write data ]
>>> [ perf record: Captured and wrote 303.795 MB perf.data (~13272985 samples) ]
>>> 2162.08user 176.24system 0:12.97elapsed 18021%CPU (0avgtext+0avgdata
>>> 1187208maxresident)k
>>> 0inputs+622624outputs (0major+1360285minor)pagefaults 0swaps
>>>
>>> - per-process collection:
>>>
>>> [ perf record: Woken up 5 times to write data ]
>>> [ perf record: Captured and wrote 1.079 MB perf.data (~47134 samples) ]
>>> 2102.39user 153.88system 0:12.78elapsed 17645%CPU (0avgtext+0avgdata
>>> 1187156maxresident)k
>>> 0inputs+2272outputs (0major+1181660minor)pagefaults 0swaps
>>>
>>> Elapsed times look similar. Data file sizes differ significantly.
>>
>> Interesting. I wonder if that's because we're losing samples due to
>> hammering the rb, or if that's a side-effect of this patch.
>>
>> Does perf report describe any lost chunks?
>>
>> For comparison, can you give --per-thread a go prior to these patches
>> being applied?
> 
> FWIW, I had a go with (an old) perf record on an arm64 system using
> --per-thread, and I see that no samples are recorded, which seems like a
> bug.
> 
> With --per-thread, the slwodown was ~20%, whereas with the defaults it
> was > 400%.

That looks similar to what I am observing in per-process single thread 
profiling >4x slowdown.

> 
> Thanks,
> Mark.
>