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authorFrederic Weisbecker <fweisbec@gmail.com>2015-01-28 01:24:09 +0100
committerIngo Molnar <mingo@kernel.org>2015-02-04 07:52:30 +0100
commitbfd9b2b5f80e7289fdd50210afe4d9ca5952a865 (patch)
treedd65ba421f2c4e7081b6797bb6c87c97ad2c6c9c /kernel/sched
parent9659e1eeee28f7025b6545934d644d19e9c6e603 (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')
-rw-r--r--kernel/sched/core.c11
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:
* - explicit schedule() call
* - return from syscall or exception to user-space
* - return from interrupt-handler to user-space
+ *
+ * WARNING: all callers must re-check need_resched() afterward and reschedule
+ * accordingly in case an event triggered the need for rescheduling (such as
+ * an interrupt waking up a task) while preemption was disabled in __schedule().
*/
static void __sched __schedule(void)
{
@@ -2773,7 +2777,6 @@ static void __sched __schedule(void)
struct rq *rq;
int cpu;
-need_resched:
preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
@@ -2840,8 +2843,6 @@ need_resched:
post_schedule(rq);
sched_preempt_enable_no_resched();
- if (need_resched())
- goto need_resched;
}
static inline void sched_submit_work(struct task_struct *tsk)
@@ -2861,7 +2862,9 @@ asmlinkage __visible void __sched schedule(void)
struct task_struct *tsk = current;
sched_submit_work(tsk);
- __schedule();
+ do {
+ __schedule();
+ } while (need_resched());
}
EXPORT_SYMBOL(schedule);