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SubjectRe: [External] Re: [PATCH 1/2] perf sched timehist: Fix -g/--call-graph option failure
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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@bytedance.com> 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

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