Re: [PATCH v7 0/6] perf record: Track sideband events for all CPUs when tracing selected CPUs

[Ravi Bangoria]

>> Number of actual samples are same ~38K. However, the perf.data file is 5x
>> bigger because of additional sideband data.
> 
> Yes, if record system wide sideband data, the amount of sideband events will increase proportionally, which is expected.
> 
>>
>> I'm pretty sure we don't need most of those additional data. So, thinking
>> loud, should we post-process perf.data file and filter out unnecessary data?
>>
> 
> I wonder if we can add a new function in perf inject.

Ok. perf inject is one option. But shall we do it bydefault in perf-record?
It's needed only when profiling target is set of cpus, not for systemwide or
per-process mode.

> By reading perf.data and comparing tid of SAMPLE events and sideband events, we can filter out the sideband data of unmatched tasks.

Yup. But AFAIK, perf-record keeps writing to perf.data and never does post-
processing on it. So adding support for this will take a bit of effort. Not
sure if we should do it as part of this series.

Thanks,
Ravi