Messages in this thread | | | Date | Mon, 28 Jun 2010 17:29:26 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC][PATCH 05/11] perf: register pmu implementations |
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On Mon, Jun 28, 2010 at 05:16:37PM +0200, Peter Zijlstra wrote: > > > } > > > + srcu_read_unlock(&pmus_srcu, idx); > > > > > > return pmu; > > > } > > > > > > > > I'm still not sure why all this locking is needed. We don't even > > support pmus in modules. > > > > Is there something coming soon that will use this? > > I remember something about KVM. > > Possibly, not sure. We could put the unregister thing in a later patch, > but I wanted to make sure it was sanely possibly and its only a few > lines of code.
Ok.
> > And who will have to use srcu? It seems the event fastpath would > > be concerned, right? Will that have an impact on the performances? > > Only event creation like above (perf_init_event) will have to use SRCU, > so not really a hot path.
Ah I see. The event itself is synchronized against the fast-path using rcu. And then pmus themselves would be synchronized against events. Right that makes sense.
But then why RCU (or SRCU, whatever)? I mean parent event creation is quite rare. And child events won't need to be synchronized as far as the parent keeps a reference to the pmu.
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