Commit 87dcbc06 authored Sep 28, 2015 by Peter Zijlstra Committed by Ingo Molnar Oct 06, 2015

sched/core: Simplify INIT_PREEMPT_COUNT



As per the following commit:

  d86ee480 ("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>

parent fe191592

include/linux/sched.h

+5 −6

Original line number	Diff line number	Diff line
		@@ -606,13 +606,12 @@ 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