* Wildly different output sizes between subsequent perf record runs.
@ 2017-11-04 1:57 Bram Stolk
2017-11-06 12:06 ` Milian Wolff
0 siblings, 1 reply; 3+ messages in thread
From: Bram Stolk @ 2017-11-04 1:57 UTC (permalink / raw)
To: linux-perf-users
If I do subsequent runs of 'perf record', both of which are identical,
I sometimes get wildly different output sizes.
https://gist.github.com/stolk/3666b2b4d4319764fdff4a2d4c619782
The binary did the same amount of work, and took the same amount of
time to execute.
This is with using perf from Ubuntu LTS.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Wildly different output sizes between subsequent perf record runs.
2017-11-04 1:57 Wildly different output sizes between subsequent perf record runs Bram Stolk
@ 2017-11-06 12:06 ` Milian Wolff
2017-11-06 17:38 ` Bram Stolk
0 siblings, 1 reply; 3+ messages in thread
From: Milian Wolff @ 2017-11-06 12:06 UTC (permalink / raw)
To: Bram Stolk; +Cc: linux-perf-users, Arnaldo Carvalho
On Samstag, 4. November 2017 02:57:01 CET Bram Stolk wrote:
> If I do subsequent runs of 'perf record', both of which are identical,
> I sometimes get wildly different output sizes.
>
>
> https://gist.github.com/stolk/3666b2b4d4319764fdff4a2d4c619782
>
> The binary did the same amount of work, and took the same amount of
> time to execute.
> This is with using perf from Ubuntu LTS.
I think this is the same bug that I have raised before. See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1479712.html and below.
Can you try to run your command with a constant period (`-c 3000000` or
similar), instead of using a dynamic period (i.e. `--freq`)? Does the issue go
away then? If yes, then it's the same issue that I described earlier, which
noone else from the perf team has acknowledged so far. I know multiple people
who are affected by this though...
--
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Wildly different output sizes between subsequent perf record runs.
2017-11-06 12:06 ` Milian Wolff
@ 2017-11-06 17:38 ` Bram Stolk
0 siblings, 0 replies; 3+ messages in thread
From: Bram Stolk @ 2017-11-06 17:38 UTC (permalink / raw)
To: Milian Wolff; +Cc: linux-perf-users, Arnaldo Carvalho
Thanks Milian,
This issue is too elusive.
Today I can no longer reproduce the issue with short data runs, even
though I use the same perf binary on the same system with same
arguments.
Not sure what has changed.
I'll try to reboot and try again, see if I can trigger it on a 'colder' machine.
On Mon, Nov 6, 2017 at 4:06 AM, Milian Wolff <milian.wolff@kdab.com> wrote:
> On Samstag, 4. November 2017 02:57:01 CET Bram Stolk wrote:
>> If I do subsequent runs of 'perf record', both of which are identical,
>> I sometimes get wildly different output sizes.
>>
>>
>> https://gist.github.com/stolk/3666b2b4d4319764fdff4a2d4c619782
>>
>> The binary did the same amount of work, and took the same amount of
>> time to execute.
>> This is with using perf from Ubuntu LTS.
>
> I think this is the same bug that I have raised before. See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1479712.html and below.
>
> Can you try to run your command with a constant period (`-c 3000000` or
> similar), instead of using a dynamic period (i.e. `--freq`)? Does the issue go
> away then? If yes, then it's the same issue that I described earlier, which
> noone else from the perf team has acknowledged so far. I know multiple people
> who are affected by this though...
>
> --
> Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
> KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
> Tel: +49-30-521325470
> KDAB - The Qt Experts
>
>
--
Owner/Director of Game Studio Abraham Stolk Inc.
Vancouver BC, Canada
b.stolk@gmail.com
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-11-04 1:57 Wildly different output sizes between subsequent perf record runs Bram Stolk
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