Re: [External] Re: [PATCH 1/2] perf sched timehist: Fix -g/--call-graph option failure
From: Arnaldo Carvalho de Melo
Date: Sat Mar 30 2024 - 10:48:35 EST
On Fri, Mar 29, 2024 at 09:08:01AM -0700, Ian Rogers wrote:
> On Thu, Mar 28, 2024 at 8:02 PM Yang Jihong <yangjihong@xxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > Sorry, due to the new email settings, the last reply email was in html
> > format, resend it now.
> >
> > On 3/29/24 00:02, Ian Rogers wrote:
> > > On Wed, Mar 27, 2024 at 10:59 PM Yang Jihong <yangjihong@xxxxxxxxxxxxx> wrote:
> > >>
> > >> When perf-sched enables the call-graph recording, sample_type of dummy
> > >> event does not have PERF_SAMPLE_CALLCHAIN, timehist_check_attr() checks
> > >> that the evsel does not have a callchain, and set show_callchain to 0.
> > >>
> > >> Currently perf sched timehist only saves callchain when processing
> > >> sched:sched_switch event, timehist_check_attr() only needs to determine
> > >> whether the event has PERF_SAMPLE_CALLCHAIN.
> > >>
> > >> Before:
> > >> # perf sched record -g true
> > >> [ perf record: Woken up 0 times to write data ]
> > >> [ perf record: Captured and wrote 4.153 MB perf.data (7536 samples) ]
> > >> # perf sched timehist
> > >> Samples do not have callchains.
> > >> time cpu task name wait time sch delay run time
> > >> [tid/pid] (msec) (msec) (msec)
> > >> --------------- ------ ------------------------------ --------- --------- ---------
> > >> 147851.826019 [0000] perf[285035] 0.000 0.000 0.000
> > >> 147851.826029 [0000] migration/0[15] 0.000 0.003 0.009
> > >> 147851.826063 [0001] perf[285035] 0.000 0.000 0.000
> > >> 147851.826069 [0001] migration/1[21] 0.000 0.003 0.006
> > >> <SNIP>
> > >>
> > >> After:
> > >> # perf sched record -g true
> > >> [ perf record: Woken up 1 times to write data ]
> > >> [ perf record: Captured and wrote 2.572 MB perf.data (822 samples) ]
> > >> # perf sched timehist
> > >> time cpu task name wait time sch delay run time
> > >> [tid/pid] (msec) (msec) (msec)
> > >> --------------- ------ ------------------------------ --------- --------- ---------
> > >> 144193.035164 [0000] perf[277062] 0.000 0.000 0.000 __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __wait_for_common <- wait_for_completion
> > >> 144193.035174 [0000] migration/0[15] 0.000 0.003 0.009 __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- smpboot_thread_fn <- kthread <- ret_from_fork
> > >> 144193.035207 [0001] perf[277062] 0.000 0.000 0.000 __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __wait_for_common <- wait_for_completion
> > >> 144193.035214 [0001] migration/1[21] 0.000 0.003 0.007 __traceiter_sched_switch <- __traceiter_sched_switch <- __sched_text_start <- smpboot_thread_fn <- kthread <- ret_from_fork
> > >> <SNIP>
> > >
> > > This looks good, should there be a Fixes tag for the sake of backports?
> > >
> > The direct cause is commit 9c95e4ef0657 ("perf evlist: Add
> > evlist__findnew_tracking_event() helper"). perf-record uses
> > evlist__add_aux_dummy() to replace evlist__add_dummy() to add a dummy
> > event. The difference is that evlist__add_aux_dummy() sets
> > no_aux_samples to true (this is expected behavior, for dummy event, no
> > need to sample aux data), resulting in evsel__config() not adding the
> > PERF_SAMPLE_CALLCHAIN bit to dummy's sample_type.
> >
> > In summary, the direct cause is the problem introduced by commit
> > 9c95e4ef0657 ("perf evlist: Add evlist__findnew_tracking_event()
> > helper"), but the root cause is the timehist_check_attr() logic problem,
> > The dummy event itself does not need to have PERF_SAMPLE_CALLCHAIN, so
> > there is no need to check it.
> >
> >
> > So, maybe add fixes-tag:
> >
> > Fixes: 9c95e4ef0657 ("perf evlist: Add evlist__findnew_tracking_event()
> > helper")
> >
> > If it is ok, I will send v2 version with this fixes-tag.
>
> I think the maintainer can add the fixes tag when they add the reviewed-by tag:
I usually do this, but if the submitter does it I'll have just to check
that it is the right tag, helps a bit in processing.
- Arnaldo
> Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
>
> Thanks,
> Ian
>
> > Thanks,
> > Yang