linux-kernel - Re: [RFC][PATCH 05/11] perf: register pmu implementations

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Date:	Mon, 28 Jun 2010 15:21:04 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	paulus <paulus@...ba.org>,
	stephane eranian <eranian@...glemail.com>,
	Robert Richter <robert.richter@....com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Yanmin <yanmin_zhang@...ux.intel.com>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 05/11] perf: register pmu implementations

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.


> +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.

And who will have to use srcu? It seems the event fastpath would
be concerned, right? Will that have an impact on the performances?



> @@ -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.

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