linux-kernel - Re: A problem about 'perf sched latency'

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Message-ID: <20180208005724.GB24686@sejong>
Date:   Thu, 8 Feb 2018 09:57:24 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     "Du, Changbin" <changbin.du@...el.com>
Cc:     jolsa@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        kernel-team@....com
Subject: Re: A problem about 'perf sched latency'

Hello,

On Tue, Feb 06, 2018 at 09:50:02PM +0800, Du, Changbin wrote:
> Hello all,
> I am using perf sched tool to analyzer sched data on my machine. But it seems that 
> 'perf sched latency' report incorrect 'Switches'. What I did is as below.
> 
> First, record...
> $ sudo perf sched record time pi 2000000 > /dev/null
> 
> Then check statistics. It says 'pi' only sched-in 1 time.
> $ sudo ./perf sched latency | grep pi
>   compiz:4054           |      6.389 ms |       30 | avg:    0.023 ms | max:    0.122 ms | max at:  94546.021080 s
>   pi:4059               |   2083.241 ms |        1 | avg:    0.007 ms | max:    0.007 ms | max at:  94545.201435 s
> 
> But the sched event show 'pi' has been sched-in 7 times.
> $ sudo ./perf sched script | grep pi:
>               pi  4059 [001] 94545.820858:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1:32237 [120]
>      kworker/1:1 32237 [001] 94545.820868:       sched:sched_switch: kworker/1:1:32237 [120] R ==> pi:4059 [120]
>               pi  4059 [001] 94545.885412:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1H:320 [100]
>     kworker/1:1H   320 [001] 94545.885419:       sched:sched_switch: kworker/1:1H:320 [100] R ==> pi:4059 [120]
>               pi  4059 [001] 94545.907869:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1H:320 [100]
>     kworker/1:1H   320 [001] 94545.907875:       sched:sched_switch: kworker/1:1H:320 [100] R ==> pi:4059 [120]
>               pi  4059 [001] 94545.908104:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1H:320 [100]
>     kworker/1:1H   320 [001] 94545.908108:       sched:sched_switch: kworker/1:1H:320 [100] R ==> pi:4059 [120]
>               pi  4059 [001] 94545.916135:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1H:320 [100]
>     kworker/1:1H   320 [001] 94545.916154:       sched:sched_switch: kworker/1:1H:320 [100] R ==> pi:4059 [120]
>               pi  4059 [001] 94546.812856:       sched:sched_switch: pi:4059 [120] S ==> kworker/1:1:32237 [120]
>      kworker/1:1 32237 [001] 94546.813148:       sched:sched_switch: kworker/1:1:32237 [120] R ==> pi:4059 [120]
>               pi  4059 [001] 94546.885227:       sched:sched_switch: pi:4059 [120] S ==> i915/signal:1:207 [98]
>    i915/signal:1   207 [001] 94546.885232:       sched:sched_switch: i915/signal:1:207 [98] D ==> pi:4059 [120]
>               pi  4059 [001] 94547.285049:       sched:sched_switch: pi:4059 [120] x ==> swapper/1:0 [120]
> 
> Does anyone know why? Thank you! :)

It seems your data doesn't have wakeup event which is required by the
'perf sched latency'.

Thanks,
Namhyung


> 
> -- 
> Thanks,
> Changbin Du
> --
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