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sched/core: Simplify INIT_PREEMPT_COUNT

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As per the following commit:

  d86ee4809d ("sched: optimize cond_resched()")

we need PREEMPT_ACTIVE to avoid cond_resched() from working before
the scheduler is set up.

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>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2015-09-28 17:45:40 +02:00 committed by Ingo Molnar
parent fe19159225
commit 87dcbc0610
1 changed files with 5 additions and 6 deletions
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11
include/linux/sched.h
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@ -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()->init_idle_preempt_count().
*/
#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.