On 04/16/2013 05:10 AM, Ingo Molnar wrote:
* Waiman Long<[email protected]> wrote:--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3021,9 +3021,6 @@ static inline bool owner_running(struct mutex *lock, struct task_struct *owner) */ 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()) @@ -3040,6 +3037,27 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) */ return lock->owner == NULL; } + +/* + * Initial check for entering the mutex spinning loop + */ +int mutex_can_spin_on_owner(struct mutex *lock) +{ + int retval = 1; + + if (!sched_feat(OWNER_SPIN)) + return 0; + + rcu_read_lock(); + if (lock->owner) + retval = lock->owner->on_cpu; + rcu_read_unlock(); + /* + * if lock->owner is not set, the mutex owner may have just acquired + * it and not set the owner yet or the mutex has been released. + */ + return retval; +}The SCHED_FEAT_OWNER_SPIN was really just an early hack we did to make with/without mutex-spinning testable.
I see.
I'd suggest a preparatory patch that gets rid of that flag and moves these two functions from sched/core.c to mutex.c where they belong. This will also allow the removal of the mutex prototypes from sched.h.
Yes, I can certainly prepare a patch to remove SCHED_FEAT_OWNER_SPIN & move those functions back to mutex.c after my patch set goes in. As for the timing, do you want me to do it now or it can wait as I will start my vacation later this week and will be back by the end of the month.
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