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Message-ID: <f5b4e1e4-9966-c22a-1628-b3df37523841@intel.com>
Date:   Tue, 20 Jun 2023 21:49:14 +0300
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Subject: Re: [PATCH 0/2] perf/core: deliver PERF_RECORD_COMM and
 PERF_RECORD_MMAP side-band events to all online cpus
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To:     Yang Jihong <yangjihong1@huawei.com>, peterz@infradead.org,
        mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com,
        alexander.shishkin@linux.intel.com, jolsa@kernel.org,
        namhyung@kernel.org, irogers@google.com,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230620155515.101222-1-yangjihong1@huawei.com>
From:   Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
In-Reply-To: <20230620155515.101222-1-yangjihong1@huawei.com>
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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(-)
>