Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

[Namhyung Kim]

On December 10, 2015 5:01:18 PM GMT+09:00, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
>* Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
>> Hello,
>> 
>> This patchset if an attempt to support multi-threading in perf top.
>> In fact, perf top already run on two threads - a worker thread and a
>> display thread.  However processing all samples with a single thread
>> in a large machine can have scalability problems.
>> 
>> This patchset extends it to have multiple worker threads to process
>> samples concurrently.  Users can control the number of threads using
>>  --num-thread option.  And there's a collector thread for passing
>hist
>> entries from worker threads to the display thread.
>
>Could you please make the number of threads default to the number of
>CPUs?
>
>Since perf top is doing one perf event per CPU anyway, that's a pretty
>natural 
>model.
>
>( I think 'perf record' should use per CPU threads as well to receive
>events, to 
>address the 'IO overload' problems with -g recording on larger CPU
>counts. )

IIRC David said that thread per cpu seems too much
especially on a large system (like ~1024 cpu).  I have no idea 
what's the reasonable default on the system, so I chose 1/4 
of map buffers (i.e. cpus for most cases). But I think I should
take non-system-wide mode into account too.

Thanks
Namhyung

Hi Ingo,
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