Messages in this thread | | | Subject | Re: disabling group leader perf_event | From | Peter Zijlstra <> | Date | Mon, 06 Sep 2010 13:54:05 +0200 |
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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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