linux-kernel - Re: [PATCH 0/2] perf/core: deliver PERF_RECORD_COMM and PERF_RECORD

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Date:   Tue, 20 Jun 2023 21:49:14 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Yang Jihong <yangjihong1@...wei.com>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] perf/core: deliver PERF_RECORD_COMM and
 PERF_RECORD_MMAP side-band events to all online cpus

On 20/06/23 18:55, Yang Jihong wrote:
> Tasks are migrated between cores due to scheduling.
> If perf samples specified CPUs, PERF_RECORD_COMM and PERF_RECORD_MMAP
> events need be deliver to all cores to avoids the problem that the comm
> and symbols cannot be parsed due to task migration to the target core.
> 
> The specific scenarios are as follows:
> 
>          CPU0                                 CPU1
>   perf record -C 0 start
>                               taskA starts to be created and executed
>                                 -> PERF_RECORD_COMM and PERF_RECORD_MMAP
>                                    events only deliver to CPU1
>                               ......
>                                 |
>                           migrate to CPU0
>                                 |
>   Running on CPU0    <----------/
>   ...
> 
>   perf record -C 0 stop
> 
> Now perf samples the PC of taskA. However, perf does not record the
> PERF_RECORD_COMM and PERF_RECORD_COMM events of taskA.
> Therefore, the comm and symbols of taskA cannot be parsed.

perf record deals with this for PERF_RECORD_TEXT_POKE, by opening
the corresponding "dummy" event on each CPU irrespective of whether
the main events are on selected CPUs.  Refer
evlist__add_dummy_on_all_cpus().

So this could be handled by perf record.

> 
> Yang Jihong (2):
>   perf/core: perf_iterate_sb_cpu() supports to receive side-band events
>     for all oneline cpus
>   perf/core: deliver PERF_RECORD_COMM and PERF_RECORD_MMAP side-band
>     events to all online cpus
> 
>  kernel/events/core.c | 58 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 41 insertions(+), 17 deletions(-)
>