[PATCH v2 01/12] sched: Simplify INIT_PREEMPT_COUNT

[Peter Zijlstra <peterz@infradead.org>]

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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().
  */
-#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.