Re: disabling group leader perf_event

[Avi Kivity <avi@redhat.com>]

  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.

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?

-- 
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