Messages in this thread | | | Date | Wed, 7 Apr 2010 13:56:27 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH] perf: Store active software events in a hashlist |
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On Tue, Apr 06, 2010 at 05:27:33PM +0200, Peter Zijlstra wrote: > On Mon, 2010-04-05 at 16:08 +0200, Frederic Weisbecker wrote: > > Each time a software event triggers, we need to walk through > > the entire list of events from the current cpu and task contexts > > to retrieve a running perf event that matches. > > We also need to check a matching perf event is actually counting. > > > > This walk is wasteful and makes the event fast path scaling > > down with a growing number of events running on the same > > contexts. > > > > To solve this, we store the running perf events in a hashlist to > > get an immediate access to them against their type:event_id when > > they trigger. > > So we have a hash-table per-cpu, each event takes a ref on the hash > table, when the thing is empty we free it. > > When the event->cpu == -1 (all cpus) we take a ref on all possible cpu's > hash-table (should be online I figure, but that requires adding a > hotplug handler). > > Then on event enable/disable we actually add the event to the hash-table > belonging to the cpu the event/task gets scheduled on, since each event > can only ever be active on one cpu. > > Right?
Exactly.
> > So looks good, altough I think we want to do that online/hotplug thing.
That would let us allocate on online cpus instead of possibles? Yeah right.
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