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SubjectRe: disabling group leader perf_event
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On Mon, 2010-09-06 at 14:34 +0300, Avi Kivity wrote:
> On 09/06/2010 02:24 PM, Peter Zijlstra wrote:
> > On Mon, 2010-09-06 at 12:12 +0300, Avi Kivity wrote:
> >> If I read the code correctly, disabling a group leader perf_event will
> >> disable the entire group.
> >>
> >> Is this correct?
> > Yeah, pretty much.
>
> Well, I never liked group_leader style APIs. I like different types for
> the container and the contained. But such is not unix.
>
> >> If so, how can I disable just the event itself? Can I allocate a dummy
> >> invent for the group leader so I can enable and disable each perf_event
> >> in the group individually?
> > Which makes me wonder why you use groups in the first place.
>
> Basically, to read() all events in one go. I have many of them.
>
> My current problem is that I have an event (kvm_exit) which I want to
> drill down by looking at a field (exit_reason). So I create lots of
> separate perf_events with a filter for each reason:
> kvm_exit(exit_reason==0), kvm_exit(exit_reason==1), etc. But filters
> are fairly slow (can have ~60 such events on AMD), so I want to make
> this drill-down optional.

Yeah, filters suck.

So what you're basically trying to do is create some histogram of
exit_reason?

Being able to make histograms in-kernel has been on the todo list for a
long while, its just that I never could come up with a sane
interface.. :/

> Current plan is to have a group for the basic events and another group
> for the drilldown events (each per-cpu), and activate the drilldown
> group on user request. perf will be able to schedule both groups
> concurrently since they only contain tracepoints, yes?

More or less, yeah (the scheduling of software and hardware events isn't
properly separated atm -- am working on that). Software events have no
scheduling constraints and should always get scheduled.




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