diff options
author | Frederic Weisbecker <fweisbec@gmail.com> | 2015-01-27 19:24:09 -0500 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2015-02-04 01:52:30 -0500 |
commit | bfd9b2b5f80e7289fdd50210afe4d9ca5952a865 (patch) | |
tree | dd65ba421f2c4e7081b6797bb6c87c97ad2c6c9c /kernel/sched/core.c | |
parent | 9659e1eeee28f7025b6545934d644d19e9c6e603 (diff) |
sched: Pull resched loop to __schedule() callers
__schedule() disables preemption during its job and re-enables it
afterward without doing a preemption check to avoid recursion.
But if an event happens after the context switch which requires
rescheduling, we need to check again if a task of a higher priority
needs the CPU. A preempt irq can raise such a situation. To handle that,
__schedule() loops on need_resched().
But preempt_schedule_*() functions, which call __schedule(), also loop
on need_resched() to handle missed preempt irqs. Hence we end up with
the same loop happening twice.
Lets simplify that by attributing the need_resched() loop responsibility
to all __schedule() callers.
There is a risk that the outer loop now handles reschedules that used
to be handled by the inner loop with the added overhead of caller details
(inc/dec of PREEMPT_ACTIVE, irq save/restore) but assuming those inner
rescheduling loop weren't too frequent, this shouldn't matter. Especially
since the whole preemption path is now losing one loop in any case.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1422404652-29067-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/core.c')
-rw-r--r-- | kernel/sched/core.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 5091fd4feed8..b269e8a2a516 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c | |||
@@ -2765,6 +2765,10 @@ again: | |||
2765 | * - explicit schedule() call | 2765 | * - explicit schedule() call |
2766 | * - return from syscall or exception to user-space | 2766 | * - return from syscall or exception to user-space |
2767 | * - return from interrupt-handler to user-space | 2767 | * - return from interrupt-handler to user-space |
2768 | * | ||
2769 | * WARNING: all callers must re-check need_resched() afterward and reschedule | ||
2770 | * accordingly in case an event triggered the need for rescheduling (such as | ||
2771 | * an interrupt waking up a task) while preemption was disabled in __schedule(). | ||
2768 | */ | 2772 | */ |
2769 | static void __sched __schedule(void) | 2773 | static void __sched __schedule(void) |
2770 | { | 2774 | { |
@@ -2773,7 +2777,6 @@ static void __sched __schedule(void) | |||
2773 | struct rq *rq; | 2777 | struct rq *rq; |
2774 | int cpu; | 2778 | int cpu; |
2775 | 2779 | ||
2776 | need_resched: | ||
2777 | preempt_disable(); | 2780 | preempt_disable(); |
2778 | cpu = smp_processor_id(); | 2781 | cpu = smp_processor_id(); |
2779 | rq = cpu_rq(cpu); | 2782 | rq = cpu_rq(cpu); |
@@ -2840,8 +2843,6 @@ need_resched: | |||
2840 | post_schedule(rq); | 2843 | post_schedule(rq); |
2841 | 2844 | ||
2842 | sched_preempt_enable_no_resched(); | 2845 | sched_preempt_enable_no_resched(); |
2843 | if (need_resched()) | ||
2844 | goto need_resched; | ||
2845 | } | 2846 | } |
2846 | 2847 | ||
2847 | static inline void sched_submit_work(struct task_struct *tsk) | 2848 | static inline void sched_submit_work(struct task_struct *tsk) |
@@ -2861,7 +2862,9 @@ asmlinkage __visible void __sched schedule(void) | |||
2861 | struct task_struct *tsk = current; | 2862 | struct task_struct *tsk = current; |
2862 | 2863 | ||
2863 | sched_submit_work(tsk); | 2864 | sched_submit_work(tsk); |
2864 | __schedule(); | 2865 | do { |
2866 | __schedule(); | ||
2867 | } while (need_resched()); | ||
2865 | } | 2868 | } |
2866 | EXPORT_SYMBOL(schedule); | 2869 | EXPORT_SYMBOL(schedule); |
2867 | 2870 | ||