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Subject: Re: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage
From: Peter Zijlstra <peterz@infradead.org>
To: bharata@linux.vnet.ibm.com
Cc: linux-kernel@vger.kernel.org, Dhaval Giani <dhaval.giani@gmail.com>,
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Date: Thu, 14 Oct 2010 10:57:30 +0200
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On Tue, 2010-10-12 at 13:21 +0530, Bharata B Rao wrote:
> +static u64 tg_request_cfs_quota(struct task_group *tg)
> +{
> +       struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
> +       u64 delta = 0;
> +
> +       if (cfs_b->runtime > 0 || cfs_b->quota == RUNTIME_INF) {
> +               raw_spin_lock(&cfs_b->lock);
> +               /*
> +                * it's possible a bandwidth update has changed the global
> +                * pool.
> +                */
> +               if (cfs_b->quota == RUNTIME_INF)
> +                       delta = sched_cfs_bandwidth_slice();
> +               else {
> +                       delta = min(cfs_b->runtime,
> +                                       sched_cfs_bandwidth_slice());
> +                       cfs_b->runtime -= delta;
> +               }
> +               raw_spin_unlock(&cfs_b->lock);
> +       }
> +       return delta;
> +} 

Since you check cfs_b->quote outside of cfs_b->lock anyway, you might as
well avoid taking the lock in that case and directly return slice.

Also, you possibly evaluate sched_cfs_bandwidth_slice() twice.