linux-kernel - Re: [PATCH 2/2] nohz: use delayed iowait accounting to avoid race on idle time stats

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Message-ID: <20140417100906.GP13658@twins.programming.kicks-ass.net>
Date:	Thu, 17 Apr 2014 12:09:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 2/2] nohz: use delayed iowait accounting to avoid race on
 idle time stats

On Thu, Apr 17, 2014 at 12:05:19PM +0200, Peter Zijlstra wrote:
> +static inline void iowait_start(struct rq *rq)
> +{
> +	raw_spin_lock(&rq->iowait_lock);
> +	rq->nr_iowait++;
> +	raw_spin_unlock(&rq->iowait_lock);
> +	current->in_iowait = 1;
> +}
> +
> +static inline void iowait_stop(struct rq *rq)
> +{
> +	current->in_iowait = 0;
> +	raw_spin_lock(&rq->iowait_lock);
> +	rq->nr_iowait--;
> +	if (!rq->nr_iowait && rq != this_rq())
> +		rq->last_iowait = ktime_get();
> +	raw_spin_unlock(&rq->iowait_lock);
> +}

We could actually use lockref here...
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