diff options
author | Peter Zijlstra <peterz@infradead.org> | 2013-01-22 02:39:13 -0500 |
---|---|---|
committer | Gleb Natapov <gleb@redhat.com> | 2013-01-29 08:38:37 -0500 |
commit | 7b270f609982f68f2433442bf167f735e7364b06 (patch) | |
tree | 07430a425125c1938fad3befc6debec667310ec4 /kernel | |
parent | c7c9c56ca26f7b9458711b2d78b60b60e0d38ba7 (diff) |
sched: Bail out of yield_to when source and target runqueue has one task
In case of undercomitted scenarios, especially in large guests
yield_to overhead is significantly high. when run queue length of
source and target is one, take an opportunity to bail out and return
-ESRCH. This return condition can be further exploited to quickly come
out of PLE handler.
(History: Raghavendra initially worked on break out of kvm ple handler upon
seeing source runqueue length = 1, but it had to export rq length).
Peter came up with the elegant idea of return -ESRCH in scheduler core.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Raghavendra, Checking the rq length of target vcpu condition added.(thanks Avi)
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Andrew Jones <drjones@redhat.com>
Tested-by: Chegu Vinod <chegu_vinod@hp.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/sched/core.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0533496b6228..01edad9b5d71 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c | |||
@@ -4316,7 +4316,10 @@ EXPORT_SYMBOL(yield); | |||
4316 | * It's the caller's job to ensure that the target task struct | 4316 | * It's the caller's job to ensure that the target task struct |
4317 | * can't go away on us before we can do any checks. | 4317 | * can't go away on us before we can do any checks. |
4318 | * | 4318 | * |
4319 | * Returns true if we indeed boosted the target task. | 4319 | * Returns: |
4320 | * true (>0) if we indeed boosted the target task. | ||
4321 | * false (0) if we failed to boost the target. | ||
4322 | * -ESRCH if there's no task to yield to. | ||
4320 | */ | 4323 | */ |
4321 | bool __sched yield_to(struct task_struct *p, bool preempt) | 4324 | bool __sched yield_to(struct task_struct *p, bool preempt) |
4322 | { | 4325 | { |
@@ -4330,6 +4333,15 @@ bool __sched yield_to(struct task_struct *p, bool preempt) | |||
4330 | 4333 | ||
4331 | again: | 4334 | again: |
4332 | p_rq = task_rq(p); | 4335 | p_rq = task_rq(p); |
4336 | /* | ||
4337 | * If we're the only runnable task on the rq and target rq also | ||
4338 | * has only one task, there's absolutely no point in yielding. | ||
4339 | */ | ||
4340 | if (rq->nr_running == 1 && p_rq->nr_running == 1) { | ||
4341 | yielded = -ESRCH; | ||
4342 | goto out_irq; | ||
4343 | } | ||
4344 | |||
4333 | double_rq_lock(rq, p_rq); | 4345 | double_rq_lock(rq, p_rq); |
4334 | while (task_rq(p) != p_rq) { | 4346 | while (task_rq(p) != p_rq) { |
4335 | double_rq_unlock(rq, p_rq); | 4347 | double_rq_unlock(rq, p_rq); |
@@ -4337,13 +4349,13 @@ again: | |||
4337 | } | 4349 | } |
4338 | 4350 | ||
4339 | if (!curr->sched_class->yield_to_task) | 4351 | if (!curr->sched_class->yield_to_task) |
4340 | goto out; | 4352 | goto out_unlock; |
4341 | 4353 | ||
4342 | if (curr->sched_class != p->sched_class) | 4354 | if (curr->sched_class != p->sched_class) |
4343 | goto out; | 4355 | goto out_unlock; |
4344 | 4356 | ||
4345 | if (task_running(p_rq, p) || p->state) | 4357 | if (task_running(p_rq, p) || p->state) |
4346 | goto out; | 4358 | goto out_unlock; |
4347 | 4359 | ||
4348 | yielded = curr->sched_class->yield_to_task(rq, p, preempt); | 4360 | yielded = curr->sched_class->yield_to_task(rq, p, preempt); |
4349 | if (yielded) { | 4361 | if (yielded) { |
@@ -4356,11 +4368,12 @@ again: | |||
4356 | resched_task(p_rq->curr); | 4368 | resched_task(p_rq->curr); |
4357 | } | 4369 | } |
4358 | 4370 | ||
4359 | out: | 4371 | out_unlock: |
4360 | double_rq_unlock(rq, p_rq); | 4372 | double_rq_unlock(rq, p_rq); |
4373 | out_irq: | ||
4361 | local_irq_restore(flags); | 4374 | local_irq_restore(flags); |
4362 | 4375 | ||
4363 | if (yielded) | 4376 | if (yielded > 0) |
4364 | schedule(); | 4377 | schedule(); |
4365 | 4378 | ||
4366 | return yielded; | 4379 | return yielded; |