linux-kernel - Re: [PATCH] sched: Removed redundant set_current

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Message-ID: <1336396416.27020.44.camel@laptop>
Date:	Mon, 07 May 2012 15:13:36 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Sasikantha babu <sasikanth.v19@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Frank Rowand <frank.rowand@...sony.com>,
	Paul Turner <pjt@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Removed redundant set_current_state in "yield"

On Tue, 2012-04-10 at 21:15 +0530, Sasikantha babu wrote:
> Removed redundant setting current task state to TASK_RUNNING.
> 
> During yield process will always remains in TASK_RUNNING state. 

Uhm, no, if you call yield() with !TASK_RUNNING you'll block and need a
proper wakeup. That is, you can in fact abuse yield() as schedule().

> Process state of  yielded process will not change from TASK_RUNNING, so it does not 
> make sense setting the process state again to TASK_RUNNING (TASK_RUNNING -> TASK_RUNNING).

No real objections, but have you tested/verified that all users are
indeed unaffected by this change?

> Signed-off-by: Sasikantha babu <sasikanth.v19@...il.com>
> ---
>  kernel/sched/core.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 4603b9d..c2a357d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4624,7 +4624,6 @@ EXPORT_SYMBOL(__cond_resched_softirq);
>   */
>  void __sched yield(void)
>  {
> -	set_current_state(TASK_RUNNING);
>  	sys_sched_yield();
>  }
>  EXPORT_SYMBOL(yield);



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