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Date: Tue, 31 Mar 2009 16:45:23 +1100
From: Paul Mackerras <paulus@samba.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/15] perf_counter: unify and fix delayed counter wakeup
In-Reply-To: <20090330171023.153932974@chello.nl>
References: <20090330170701.856843742@chello.nl>
	<20090330171023.153932974@chello.nl>
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Peter Zijlstra writes:

> +void perf_counter_wakeup(struct perf_counter *counter)
> +{
> +	struct perf_mmap_data *data;
> +
> +	rcu_read_lock();
> +	data = rcu_dereference(counter->data);
> +	if (data) {
> +		(void)atomic_xchg(&data->wakeup, POLL_IN);

Really just a nit, but how is this atomic_xchg any different from
atomic_set(&data->wakeup, POLL_IN) aside from being slower?

Paul.