* Andi Kleen <a...@linux.intel.com> wrote:
> On Wed, Sep 25, 2013 at 02:50:26PM +0200, Jiri Olsa wrote:
> > hi,
> > sending *RFC* for toggling events support.
> >
> > Adding perf interface that allows to create toggle events, which can
> > enable or disable another event. Whenever the toggle event is triggered
> > (has overflow), it toggles another event state and either starts or
> > stops it.
> >
> > The goal is to be able to create toggling tracepoint events to enable and
> > disable HW counters, but the interface is generic enough to be used for
> > any kind of event.
>
> Haven't read the patches, but frequent full event switch in/out seems
> very expensive. If someone puts that switch on a common function it
> would likely disturb things quite a bit.
>
> It would be better to keep counting and just do RDPMC on the switch
> points, and then subtract for counting. For sampling could need a MSR
> write to enable/disable. Still somewhat expensive, but nowhere near as
> bad as a full switch.
This is essentially an optimized event switch and should probably be done
on a higher level so that other instances of event/context switching
benefit as well.
Thanks,
Ingo
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