Messages in this thread | | | Subject | Re: [RFC][PATCH 05/11] perf: register pmu implementations | From | Peter Zijlstra <> | Date | Mon, 28 Jun 2010 17:16:37 +0200 |
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On Mon, 2010-06-28 at 15:21 +0200, Frederic Weisbecker wrote: > On Thu, Jun 24, 2010 at 04:28:09PM +0200, Peter Zijlstra wrote: > > + if (bp->attr.type != PERF_TYPE_BREAKPOINT) > > + return -ENOENT; > > + > > + err = register_perf_hw_breakpoint(bp); > > + if (err) > > + return err; > > + > > + bp->destroy = bp_perf_event_destroy;
> Seems it would make sense to also have destroy in the pmu, it's the same > along every events in the same class right? > > But this can be for later.
Ah, indeed.
> > +static LIST_HEAD(pmus); > > +static DEFINE_MUTEX(pmus_lock); > > +static struct srcu_struct pmus_srcu; > > + > > +int perf_pmu_register(struct pmu *pmu) > > +{ > > + mutex_lock(&pmus_lock); > > + list_add_rcu(&pmu->entry, &pmus); > > + mutex_unlock(&pmus_lock); > > + > > + return 0; > > +} > > + > > +void perf_pmu_unregister(struct pmu *pmu) > > +{ > > + mutex_lock(&pmus_lock); > > + list_del_rcu(&pmu->entry); > > + mutex_unlock(&pmus_lock); > > > > - atomic_inc(&perf_swevent_enabled[event_id]); > > - event->destroy = sw_perf_event_destroy; > > + synchronize_srcu(&pmus_srcu); > > +} > > + > > +struct pmu *perf_init_event(struct perf_event *event) > > +{ > > + struct pmu *pmu = NULL; > > + int idx; > > + > > + idx = srcu_read_lock(&pmus_srcu); > > + list_for_each_entry_rcu(pmu, &pmus, entry) { > > + int ret = pmu->event_init(event); > > + if (!ret) > > + break; > > + if (ret != -ENOENT) { > > + pmu = ERR_PTR(ret); > > + break; > > } > > - pmu = &perf_ops_generic; > > - break; > > } > > + 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.
> 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.
> > @@ -5743,15 +5742,15 @@ perf_cpu_notify(struct notifier_block *s > > { > > unsigned int cpu = (long)hcpu; > > > > - switch (action) { > > + switch (action & ~CPU_TASKS_FROZEN) { > > > > case CPU_UP_PREPARE: > > - case CPU_UP_PREPARE_FROZEN: > > + case CPU_DOWN_FAILED: > > perf_event_init_cpu(cpu); > > break; > > > > + case CPU_UP_CANCELED: > > case CPU_DOWN_PREPARE: > > - case CPU_DOWN_PREPARE_FROZEN: > > perf_event_exit_cpu(cpu); > > break; > > > > That doesn't seem to be related to this patch initial topic.
Ah indeed, that needs to go live in its own patch.
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