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

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