On Thu, 3 Sep 2015, Dennis Gnad wrote:
>
> > as far as I can tell you can't really do this with perf (the -I option
> > only lets you get down to 100ms).
>
> Which -I option do you mean? At least it's not available for my perf record
> (kernel 3.16).
The -I option is for "perf stat". It lets you print the counters at a
regular time interval.
Something like
perf_3.16 stat -e cycles,instructions -I 100 sleep 1
>
> > I ended up trying to write a custom program to do this, but it turns out
> > the perf sampling interface has really high overhead when doing this, and
> > the interrupt throttle kicks in which makes it useless.
>
> Are you talking about the kernel interface or some interface of the perf tool?
> I think I need a minimum of 100Hz or 1000Hz, but it wouldn't be a problem if
> this is just collected in some kernel shared memory and in the end copied to
> userspace, or at a lower frequency.
The kernel itself has trouble going to 100Hz without causing a lot of
overhead and at 1kHz the NMI overhead gets high enough that the kernel
throttles things down. I haven't investigated why that is, it might be a
problem with how my tool is coded. For now I just gave up and am making
masurements at 10Hz.
Vince
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