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From: Ian Rogers <irogers@google.com>
Date: Fri, 29 Mar 2024 09:08:01 -0700
Message-ID: <CAP-5=fWDY9Aj+qHNOuwJ9yE==G=vmCzECXYEZAifOhGHX7yr6w@mail.gmail.com>
Subject: Re: [External] Re: [PATCH 1/2] perf sched timehist: Fix
 -g/--call-graph option failure
To: Yang Jihong <yangjihong@bytedance.com>
Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, 
	namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, 
	jolsa@kernel.org, adrian.hunter@intel.com, kan.liang@linux.intel.com, 
	james.clark@arm.com, linux-perf-users@vger.kernel.org, 
	linux-kernel@vger.kernel.org
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On Thu, Mar 28, 2024 at 8:02=E2=80=AFPM Yang Jihong <yangjihong@bytedance.c=
om> 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=E2=80=AFPM Yang Jihong <yangjihong@byteda=
nce.com> wrote:
> >>
> >> When perf-sched enables the call-graph recording, sample_type of dummy
> >> event does not have PERF_SAMPLE_CALLCHAIN, timehist_check_attr() check=
s
> >> 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 determin=
e
> >> 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_switc=
h <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __w=
ait_for_common <- wait_for_completion
> >>      144193.035174 [0000]  migration/0[15]                     0.000  =
    0.003      0.009    __traceiter_sched_switch <- __traceiter_sched_switc=
h <- __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_switc=
h <- __sched_text_start <- preempt_schedule_common <- __cond_resched <- __w=
ait_for_common <- wait_for_completion
> >>      144193.035214 [0001]  migration/1[21]                     0.000  =
    0.003      0.007    __traceiter_sched_switch <- __traceiter_sched_switc=
h <- __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:

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> Thanks,
> Yang