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

From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus <paulus@samba.org>,
	stephane eranian <eranian@googlemail.com>,
	Robert Richter <robert.richter@amd.com>,
	Will Deacon <will.deacon@arm.com>,
	Paul Mundt <lethal@linux-sh.org>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Lin Ming <ming.m.lin@intel.com>,
	Yanmin <yanmin_zhang@linux.intel.com>,
	Deng-Cheng Zhu <dengcheng.zhu@gmail.com>,
	David Miller <davem@davemloft.net>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 05/11] perf: register pmu implementations
Date: Mon, 28 Jun 2010 15:21:04 +0200	[thread overview]
Message-ID: <20100628132101.GB5668@nowhere> (raw)
In-Reply-To: <20100624143406.764162308@chello.nl>

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.