Messages in this thread | | | Date | Tue, 19 Nov 2013 17:14:02 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 4/5] perf record: mmap output file - v5 |
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* David Ahern <dsahern@gmail.com> wrote:
> > Well, we could exclude the profiling task itself from profiling > > events (just like ftrace and core bits of perf does it out of > > necessity), but I intentionally wanted to avoid that, to make sure > > we are honest and to make sure people don't tolerate profiling > > overhead that disturbs other workloads. > > Samples generated by perf itself need to be observable -- e.g. > process scheduling I want to see the time consumed by the data > collector itself and there are times when 'perf trace -- perf ...' > is useful.
Absolutely agreed - a measurement instrument affects the measurement, and we must not try to hide that.
Still we can try to make the disturbance smaller and more managable.
For example if I have enough RAM it should be possible to run perf record with a 1 GB ring-buffer, and in that case as long as the perf.data is smaller than 1 GB there should be no writeout or any other IO activity until the measurement ends.
Thanks,
Ingo
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