Re: [RFC 00/21] perf tools: Add toggling events support

[Ingo Molnar]

* Andi Kleen <ak@xxxxxxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/