On Wed, 30 Sep 2015 09:10:36 +0200
Peter Zijlstra <pet...@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) <pet...@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 <rost...@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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