linux-kernel - Re: [RFC][PATCH 01/10] sched: Change rt_task(prev) in pre_schedule

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Message-ID: <AANLkTimO+aBQD530btPmH3o7j931KEmFP=GKia-039wO@mail.gmail.com>
Date:	Tue, 7 Dec 2010 11:25:43 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [RFC][PATCH 01/10] sched: Change rt_task(prev) in pre_schedule_rt
 to likely

On Tue, Dec 7, 2010 at 9:58 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> From: Steven Rostedt <srostedt@...hat.com>
>
> As found with the branch annotation profiler, the unlikely(rt_task(prev))
> in pre_schedule_rt() is always wrong. In fact it should be likely due to
> the fact that we got to this function because we used prev's scheduling
> class (which had to be rt).
>
> Change the unlikely(rt_task(prev)) to likely(rt_task(prev))

I have sent a more radical patch before but it get ignored.
http://marc.info/?l=linux-kernel&m=126572702600950&w=2

>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Gregory Haskins <ghaskins@...ell.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  kernel/sched_rt.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index bea7d79..7a5c4db 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -1474,7 +1474,7 @@ skip:
>  static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
>  {
>        /* Try to pull RT tasks here if we lower this rq's prio */
> -       if (unlikely(rt_task(prev)) && rq->rt.highest_prio.curr > prev->prio)
> +       if (likely(rt_task(prev)) && rq->rt.highest_prio.curr > prev->prio)

IMHO, we can delete the checking for rt_task(prev).
Or am I missing something?

Thanks,
Yong
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