linux-kernel - Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT

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Message-ID: <20150929104332.69571e98@gandalf.local.home>
Date:	Tue, 29 Sep 2015 10:43:32 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, fweisbec@...il.com, oleg@...hat.com,
	umgwanakikbuti@...il.com, tglx@...utronix.de
Subject: Re: [RFC][PATCH 01/11] sched: Simplify INIT_PREEMPT_COUNT


[ Resend with a "Reply-all" this time! ]

On Tue, 29 Sep 2015 11:28:26 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> As per commit d86ee4809d03 ("sched: optimize cond_resched()") we need
> PREEMPT_ACTIVE to avoid cond_resched() from working before the
> scheduler is setup.
> 
> However, keeping preemption disabled should do the same thing already,
> making the PREEMPT_ACTIVE part entirely redundant.

Thus PREEMPT_ACTIVE wasn't needed at that commit either, or was it?

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/sched.h |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -608,17 +608,14 @@ struct task_cputime_atomic {
>  /*
>   * Disable preemption until the scheduler is running.
>   * Reset by start_kernel()->sched_init()->init_idle().
> - *
> - * We include PREEMPT_ACTIVE to avoid cond_resched() from working
> - * before the scheduler is active -- see should_resched().
>   */
> -#define INIT_PREEMPT_COUNT	(PREEMPT_DISABLED + PREEMPT_ACTIVE)
> +#define INIT_PREEMPT_COUNT	PREEMPT_DISABLED

I can't find anything wrong with this.

Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

>  
>  /**
>   * struct thread_group_cputimer - thread group interval timer counts
>   * @cputime_atomic:	atomic thread group interval timers.
>   * @running:		non-zero when there are timers running and
> - * 			@cputime receives updates.
> + *			@cputime receives updates.
>   *
>   * This structure contains the version of task_cputime, above, that is
>   * used for thread group CPU timer calculations.
> 

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