Re: perf sched timehist --state vs perf script

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Oct 24, 2024 at 06:36:30PM +0200, vmolnaro@redhat.com wrote:
> From: Veronika Molnarova <vmolnaro@redhat.com>
> 
> Hello!
> 
> We encountered an issue with 'perf sched timehist --state' when
> we expected for a test case that the process of a workload would 
> eventually end in the dead state(marked by 'X') and be switched
> out. This can be seen also by using 'perf script':
> 
>     # perf sched record -a sleep 1
>     [ perf record: Woken up 1 times to write data ]
>     [ perf record: Captured and wrote 0.167 MB perf.data (166 samples) ]
>     # perf script | grep sleep
>            sleep  151541 [000] 193461.410617: sched:sched_stat_runtime: comm=sleep pid=151541 runtime=3132275 [ns]
>            sleep  151541 [000] 193461.410624:       sched:sched_switch: sleep:151541 [120] S ==> swapper/0:0 [120]
>          swapper       0 [000] 193462.410688:       sched:sched_waking: comm=sleep pid=151541 prio=120 target_cpu=000
>          swapper       0 [000] 193462.410698:       sched:sched_switch: swapper/0:0 [120] R ==> sleep:151541 [120]
>          :151541  151541 [000] 193462.411100: sched:sched_stat_runtime: comm=sleep pid=151541 runtime=407210 [ns]
>          :151541  151541 [000] 193462.411107:       sched:sched_switch: sleep:151541 [120] X ==> swapper/0:0 [120]
> 
> But for the 'perf sched timehist --state' the process is shown
> in the zombie state when it is being switched out:
> 
>     # perf sched timehist --state | grep 151541
>     Samples do not have callchains.
>       193461.410624 [0000]  sleep[151541]                       0.000      0.054      3.129      S 
>       193462.411107 [0000]  :151541[151541]                     0.000      0.000      0.408      Z 
> 
> Shouldn't both commands report the same result, or is there a reason
> why 'perf script' uses the dead state while 'perf sched' uses dead?

I remember there was a discussion related to this.

https://lore.kernel.org/all/20240122070859.1394479-2-zegao@tencent.com/

And it seems it's fixed both in perf and libtraceevent.  Maybe your
libtraceevent is somewhat outdated and doesn't have the update.

> It also seems that the 'perf sched' cannot read the name of the zombie
> process, but that can be a different issue.

Hmm.. right.  It should update thread->comm using the sched_switch event.

Thanks,
Namhyung