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Re: [PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT

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On Wed, 30 Sep 2015 09:10:36 +0200
Peter Zijlstra <peterz@infradead.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.
> 
> The only complication is !PREEMPT_COUNT kernels, where
> PREEMPT_DISABLED ends up being 0. Instead we use an unconditional
> PREEMPT_OFFSET to set preempt_count() even on !PREEMPT_COUNT kernels.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  include/linux/sched.h |   11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -606,19 +606,18 @@ struct task_cputime_atomic {
>  #endif
>  
>  /*
> - * Disable preemption until the scheduler is running.
> - * Reset by start_kernel()->sched_init()->init_idle().
> + * Disable preemption until the scheduler is running -- use an unconditional
> + * value so that it also works on !PREEMPT_COUNT kernels.
>   *
> - * We include PREEMPT_ACTIVE to avoid cond_resched() from working
> - * before the scheduler is active -- see should_resched().
> + * Reset by start_kernel()->sched_init()->init_idle().

 Reset by start_kernel()->sched_init()->init_idle()->init_idle_preempt_count().

Other than that.

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

-- Steve

>   */
> -#define INIT_PREEMPT_COUNT	(PREEMPT_DISABLED + PREEMPT_ACTIVE)
> +#define INIT_PREEMPT_COUNT	PREEMPT_OFFSET
>  
>  /**
>   * 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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[PATCH v2 00/12] sched: Killing PREEMPT_ACTIVE Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
  [PATCH v2 04/12] sched: Add preempt argument to __schedule() Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
  [PATCH v2 06/12] sched: Stop setting PREEMPT_ACTIVE Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
    Re: [PATCH v2 06/12] sched: Stop setting PREEMPT_ACTIVE Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-01 17:30 +0200
  [PATCH v2 08/12] sched: Simplify preempt_count tests Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
    Re: [PATCH v2 08/12] sched: Simplify preempt_count tests Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-01 17:40 +0200
  [PATCH v2 12/12] sched: Add preempt_count invariant check Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
    Re: [PATCH v2 12/12] sched: Add preempt_count invariant check Steven Rostedt <rostedt@goodmis.org> - 2015-09-30 11:40 +0200
      Re: [PATCH v2 12/12] sched: Add preempt_count invariant check Peter Zijlstra <peterz@infradead.org> - 2015-09-30 13:20 +0200
  [PATCH v2 11/12] sched: More notrace Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
  [PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT Peter Zijlstra <peterz@infradead.org> - 2015-09-30 09:40 +0200
    Re: [PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT Steven Rostedt <rostedt@goodmis.org> - 2015-09-30 11:10 +0200
      Re: [PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT Thomas Gleixner <tglx@linutronix.de> - 2015-09-30 22:50 +0200
    Re: [PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-01 15:30 +0200

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