On Wed, Nov 02, 2011 at 01:09:46PM +0200, Gleb Natapov wrote:
> > > > The user can cause this to be very small (even zero). Can this cause an
> > > > NMI storm?
> > > >
> > > If user will set it to zero then attr.sample_period will always be 0 and
> > > perf will think that the event is non sampling and will use max_period
> > > instead. For a small value greater than zero how is it different from
> > > userspace creating an event with sample_period of 1?
> >
> > I don't know. Does the kernel survive it?
> >
> Need to test, but I do not see anything in the kernel that prevent userspace
> from setting it to any value.
>
You can set sample_period to 1 by providing -c 1 to perf top/record.
Kernel survives it easily since perf subsystem kindly throttles
interrupts for you. You can set max interrupt per event per time tick
in /proc/sys/kernel/perf_event_max_sample_rate.
--
Gleb.
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