Re: perf sched timehist --state vs perf script

[Namhyung Kim <namhyung@kernel.org>]

On Thu, Oct 31, 2024 at 12:32:31PM +0100, Michael Petlan wrote:
> On Tue, 29 Oct 2024, Namhyung Kim wrote:
> > 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?
> 
> Hello! Thanks for reacting!
> > 
> > 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 libtraceevent is somewhat outdated and doesn't have the update.
> >
> Yes! When we've updated libtraceevent to 1.8.3, both show Z now, which is
> probably correct.

Cool.

> 
> Then it comes into my mind whether shouldn't perf-sched and perf-script
> both take it from libtraceevent to unify the approaches, rather than
> perf-sched using its own implementation and perf-script taking it from
> libtraceevent... ?

Yeah, I think it's better to use libtraceevent for it.

> 
> > > 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.
> 
> According to the tests, the name seems that it used to be translated correctly
> in past, so it'd be nice if it worked again, althoug it is pretty clear which
> process it was, according to the PID. Thus, the test can be adjusted to search
> for the combination "PID, status Z", instead of "command, status Z"... I.e. to
> accept the current situation...

Sounds good.  Please send the patch.

Thanks,
Namhyung