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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-03-25 20:05:16 (GMT)
committerIngo Molnar <mingo@elte.hu>2010-04-02 18:12:04 (GMT)
commit65cc8e4859ff29a9ddc989c88557d6059834c2a2 (patch)
tree7f12c2532a92d607b5c52fa71c1799631a7a91ff /kernel/sched.c
parent0017d735092844118bef006696a750a0e4ef6ebd (diff)
downloadlinux-65cc8e4859ff29a9ddc989c88557d6059834c2a2.tar.xz
sched: Optimize task_rq_lock()
Now that we hold the rq->lock over set_task_cpu() again, we can do away with most of the TASK_WAKING checks and reduce them again to set_cpus_allowed_ptr(). Removes some conditionals from scheduling hot-paths. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Oleg Nesterov <oleg@redhat.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c23
1 files changed, 15 insertions, 8 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index dcd1773..51d336e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -914,8 +914,8 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
#endif /* __ARCH_WANT_UNLOCKED_CTXSW */
/*
- * Check whether the task is waking, we use this to synchronize against
- * ttwu() so that task_cpu() reports a stable number.
+ * Check whether the task is waking, we use this to synchronize ->cpus_allowed
+ * against ttwu().
*/
static inline int task_is_waking(struct task_struct *p)
{
@@ -932,11 +932,9 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
struct rq *rq;
for (;;) {
- while (task_is_waking(p))
- cpu_relax();
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p) && !task_is_waking(p)))
+ if (likely(rq == task_rq(p)))
return rq;
raw_spin_unlock(&rq->lock);
}
@@ -953,12 +951,10 @@ static struct rq *task_rq_lock(struct task_struct *p, unsigned long *flags)
struct rq *rq;
for (;;) {
- while (task_is_waking(p))
- cpu_relax();
local_irq_save(*flags);
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p) && !task_is_waking(p)))
+ if (likely(rq == task_rq(p)))
return rq;
raw_spin_unlock_irqrestore(&rq->lock, *flags);
}
@@ -5262,7 +5258,18 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
struct rq *rq;
int ret = 0;
+ /*
+ * Serialize against TASK_WAKING so that ttwu() and wunt() can
+ * drop the rq->lock and still rely on ->cpus_allowed.
+ */
+again:
+ while (task_is_waking(p))
+ cpu_relax();
rq = task_rq_lock(p, &flags);
+ if (task_is_waking(p)) {
+ task_rq_unlock(rq, &flags);
+ goto again;
+ }
if (!cpumask_intersects(new_mask, cpu_active_mask)) {
ret = -EINVAL;