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authorThomas Gleixner <tglx@linutronix.de>2011-06-10 15:08:55 +0200
committerIngo Molnar <mingo@elte.hu>2011-07-01 10:39:07 +0200
commit307bf9803f25a8a3f53c1012110fb74e2f893eb0 (patch)
tree72146cbf22ea0e7d36a0734cca9d46291c40ca89 /kernel
parent2a46dae38087e62dd5fb08a6dadf1407717ed13c (diff)
downloadop-kernel-dev-307bf9803f25a8a3f53c1012110fb74e2f893eb0.zip
op-kernel-dev-307bf9803f25a8a3f53c1012110fb74e2f893eb0.tar.gz
sched: Simplify mutex_spin_on_owner()
It does not make sense to rcu_read_lock/unlock() in every loop iteration while spinning on the mutex. Move the rcu protection outside the loop. Also simplify the return path to always check for lock->owner == NULL which meets the requirements of both owner changed and need_resched() caused loop exits. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1106101458350.11814@ionos Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched.c25
1 files changed, 9 insertions, 16 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 5925275..e355ee7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4306,11 +4306,8 @@ EXPORT_SYMBOL(schedule);
static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
{
- bool ret = false;
-
- rcu_read_lock();
if (lock->owner != owner)
- goto fail;
+ return false;
/*
* Ensure we emit the owner->on_cpu, dereference _after_ checking
@@ -4320,11 +4317,7 @@ static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
*/
barrier();
- ret = owner->on_cpu;
-fail:
- rcu_read_unlock();
-
- return ret;
+ return owner->on_cpu;
}
/*
@@ -4336,21 +4329,21 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
if (!sched_feat(OWNER_SPIN))
return 0;
+ rcu_read_lock();
while (owner_running(lock, owner)) {
if (need_resched())
- return 0;
+ break;
arch_mutex_cpu_relax();
}
+ rcu_read_unlock();
/*
- * If the owner changed to another task there is likely
- * heavy contention, stop spinning.
+ * We break out the loop above on need_resched() and when the
+ * owner changed, which is a sign for heavy contention. Return
+ * success only when lock->owner is NULL.
*/
- if (lock->owner)
- return 0;
-
- return 1;
+ return lock->owner == NULL;
}
#endif
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