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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
To:     Adrian Hunter <adrian.hunter@intel.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>
 <f5b4e1e4-9966-c22a-1628-b3df37523841@intel.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <d6dc0437-854f-8dad-91fc-404138d171a4@huawei.com>
Date:   Fri, 23 Jun 2023 13:48:39 +0800
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Hello,

On 2023/6/21 2:49, Adrian Hunter wrote:
> 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.

Okay, I'll take a look at it and use this solution to deal with it.

Thanks,
Yang