linux-kernel - Re: [PATCH] sched: remove an unnecessary memory access, rq->cpu in _

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Message-ID: <20160217083109.GB1197@gmail.com>
Date:	Wed, 17 Feb 2016 09:31:09 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Byungchul Park <byungchul.park@....com>
Cc:	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: remove an unnecessary memory access, rq->cpu in
 __schedule()


* Byungchul Park <byungchul.park@....com> wrote:

> Is there any reason keeping this statement on the code?
> 
> -----8<-----
> From d8a387efb8199b69b6464970d6f9fc57cbcf0ab0 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@....com>
> Date: Thu, 11 Feb 2016 11:50:53 +0900
> Subject: [PATCH] sched: remove an unnecessary memory access, rq->cpu in
>  __schedule()
> 
> Remove an unnecessary assignment of variable not used any more.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/sched/core.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1315cec..501f5d9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3193,7 +3193,6 @@ static void __sched notrace __schedule(bool preempt)
>  
>  		trace_sched_switch(preempt, prev, next);
>  		rq = context_switch(rq, prev, next); /* unlocks the rq */
> -		cpu = cpu_of(rq);
>  	} else {
>  		lockdep_unpin_lock(&rq->lock);
>  		raw_spin_unlock_irq(&rq->lock);

There's no memory access that I can see - GCC will optimize it out.

Having said that, it is a dead statement so can be removed. I fixed the title 
accordingly.

Thanks,

	Ingo