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| author | Thomas Gleixner <tglx@linutronix.de> | 2011-06-10 15:08:55 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-07-01 10:39:07 +0200 |
| commit | 307bf9803f25a8a3f53c1012110fb74e2f893eb0 (patch) | |
| tree | 72146cbf22ea0e7d36a0734cca9d46291c40ca89 /kernel | |
| parent | 2a46dae38087e62dd5fb08a6dadf1407717ed13c (diff) | |
| download | linux-307bf9803f25a8a3f53c1012110fb74e2f893eb0.tar.gz linux-307bf9803f25a8a3f53c1012110fb74e2f893eb0.tar.bz2 linux-307bf9803f25a8a3f53c1012110fb74e2f893eb0.zip | |
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.c | 25 |
1 files changed, 9 insertions, 16 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 59252754fbe0..e355ee72e83f 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 |