linux-kernel - Re: [RFC][PATCH 3/8] perf: register pmu implementations

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Date:	Wed, 16 Jun 2010 19:03:56 +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 3/8] perf: register pmu implementations

On Wed, Jun 16, 2010 at 06:00:30PM +0200, Peter Zijlstra wrote:
> +static void bp_perf_event_destroy(struct perf_event *event)
> +{
> +	release_bp_slot(event);
> +}
> +
> +static struct pmu *bp_perf_event_init(struct perf_event *bp)
> +{
> +	int err;
> +
> +	if (event->attr.type != PERF_TYPE_BREAKPOINT)
> +		return -ENOENT;
> +
> +	err = register_perf_hw_breakpoint(bp);
> +	if (err)
> +		return err;
> +
> +	bp->destroy = bp_perf_event_destroy;
> +
> +	return 0;
> +}
> +
> +static struct pmu perf_breakpoint = {
> +	.event_init	= hw_breakpoint_event_init,



Should be bp_perf_event_init?



> +	.enable		= arch_install_hw_breakpoint,
> +	.disable	= arch_uninstall_hw_breakpoint,
> +	.read		= hw_breakpoint_pmu_read,
> +};
<snip>
> +static int perf_swevent_int(struct perf_event *event)
> +{
> +	if (event->attr.type != PERF_TYPE_SOFTWARE)
> +		return -ENOENT


perf_swevent_init() ?



> +int perf_pmu_register(struct pmu *pmu)
> +{
> +	spin_lock(&pmus_lock);
> +	list_add_rcu(&pmu->entry, &pmus);
> +	spin_unlock(&pmus_lock);
> +
> +	return 0;
> +}
> +
> +void perf_pmu_unregister(struct pmu *pmu)
> +{
> +	spin_lock(&pmus_lock);
> +	list_del_rcu(&pmu->entry);
> +	spin_unlock(&pmus_lock);
> +
> +	synchronize_srcu(&pmus_srcu);
> +}



Who needs this?



> +
> +struct pmu *perf_init_event(struct perf_event *event)
> +{
> +	struct pmu *pmu;
> +	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);



This could use a simple mutex instead of a spinlock + srcu_sync on
writer and srcu on reader.

That doesn't matter much that said. What I don't understand is
why we need to synchronize the writers. Walking the list with
list_*_rcu() looks justified once we support boot events, but
until then...


For the rest of the patch, the whole idea is nice.

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