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

[Peter Zijlstra]

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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