Commit-ID: 307bf9803f25a8a3f53c1012110fb74e2f893eb0
Gitweb: http://git.kernel.org/tip/307bf9803f25a8a3f53c1012110fb74e2f893eb0
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Fri, 10 Jun 2011 15:08:55 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 1 Jul 2011 10:39:07 +0200
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@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1106101458350.11814@ionos
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/sched.c | 25 +++++++++----------------
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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