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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 11:01:40 +0200
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On Tue, 2010-10-12 at 13:21 +0530, Bharata B Rao wrote:
> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
> +               unsigned long delta_exec)
> +{
> +       if (cfs_rq->quota_assigned == RUNTIME_INF)
> +               return;
> +
> +       cfs_rq->quota_used += delta_exec;
> +
> +       if (cfs_rq->quota_used < cfs_rq->quota_assigned)
> +               return;
> +
> +       cfs_rq->quota_assigned += tg_request_cfs_quota(cfs_rq->tg);
> +}

That looks iffy, quota_assigned is only ever incremented and can wrap.
Why not subtract delta_exec and replenish when <0? That keeps the
numbers small.