[PATCH 3/4] sched: Pull preemption disablement to __schedule() caller

Frederic Weisbecker
2015-01-28T00:24:54Z

Lets factorize all preempt_count operations to the __schedule()
callers. This way we spare two preempt count changes in __schedule()
when it's called by preemption APIs.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/sched/core.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 89b165f..1c0e5b1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2760,7 +2760,6 @@ static void __sched __schedule(void)
struct rq *rq;
int cpu;

- preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_note_context_switch();
@@ -2822,8 +2821,6 @@ static void __sched __schedule(void)
raw_spin_unlock_irq(&rq->lock);

post_schedule(rq);
-
- sched_preempt_enable_no_resched();
}

static inline void sched_submit_work(struct task_struct *tsk)
@@ -2844,7 +2841,9 @@ asmlinkage __visible void __sched schedule(void)

sched_submit_work(tsk);
do {
+ preempt_disable();
__schedule();
+ sched_preempt_enable_no_resched();
} while (need_resched());
}
EXPORT_SYMBOL(schedule);
@@ -2883,9 +2882,9 @@ void __sched schedule_preempt_disabled(void)
static void preempt_schedule_common(void)
{
do {
- preempt_count_add(PREEMPT_ACTIVE);
+ preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
__schedule();
- preempt_count_sub(PREEMPT_ACTIVE);
+ preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

/*
* Check again in case we missed a preemption opportunity
@@ -2938,7 +2937,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
return;

do {
- preempt_count_add(PREEMPT_ACTIVE);
+ preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
/*
* Needs preempt disabled in case user_exit() is traced
* and the tracer calls preempt_enable_notrace() causing
@@ -2947,8 +2946,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
prev_ctx = exception_enter();
__schedule();
exception_exit(prev_ctx);
-
- preempt_count_sub(PREEMPT_ACTIVE);
+ preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
barrier();
} while (need_resched());
}
@@ -2973,11 +2971,11 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
prev_state = exception_enter();

do {
- preempt_count_add(PREEMPT_ACTIVE);
+ preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
local_irq_enable();
__schedule();
local_irq_disable();
- preempt_count_sub(PREEMPT_ACTIVE);
+ preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

/*
* Check again in case we missed a preemption opportunity
--
2.1.4