Re: [External] Re: [PATCH 1/2] perf sched timehist: Fix -g/--call-graph option failure

[Yang Jihong]

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.

Thanks,
Yang