linux-kernel - Re: [PATCH 01/15] perf_counter: unify and fix delayed counter wakeup

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Message-ID: <18897.44531.88862.844627@cargo.ozlabs.ibm.com>
Date:	Tue, 31 Mar 2009 16:45:23 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/15] perf_counter: unify and fix delayed counter wakeup

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.
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