Messages in this thread | | | Date | Thu, 26 Sep 2013 09:03:07 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC 00/21] perf tools: Add toggling events support |
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* Andi Kleen <ak@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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