linux-kernel - Re: [patch 1/3] sched: use jump labels to reduce overhead when bandwidth control is inactive

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Message-ID: <1320744563.2244.8.camel@twins>
Date:	Tue, 08 Nov 2011 10:29:23 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Turner <pjt@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 1/3] sched: use jump labels to reduce overhead when
 bandwidth control is inactive

On Mon, 2011-11-07 at 20:26 -0800, Paul Turner wrote:
> @@ -1788,6 +1791,9 @@ static void do_sched_cfs_slack_timer(str
>   */
>  static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
>  {
> +       if (!cfs_bandwidth_used())
> +               return;
> +
>         /* an active group must be handled by the update_curr()->put() path */
>         if (!cfs_rq->runtime_enabled || cfs_rq->curr)
>                 return;
> @@ -1805,6 +1811,9 @@ static void check_enqueue_throttle(struc
>  /* conditionally throttle active cfs_rq's from put_prev_entity() */
>  static void check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
>  {
> +       if (!cfs_bandwidth_used())
> +               return;
> +
>         if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
>                 return;
>   

does it matter if you pull this out into an inline function like:

static __always_inline void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
	if (cfs_bandwidth_used())
		__check_enqueue_throttle(cfs_rq);
}

That would avoid the superfluous function call as well.
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