On Thu, 2016-01-21 at 17:29 +0800, Ding Tianhong wrote: > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 0551c21..596b341 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -256,7 +256,7 @@ static inline int mutex_can_spin_on_owner(struct mutex > *lock) > struct task_struct *owner; > int retval = 1; > > - if (need_resched()) > + if (need_resched() || atomic_read(&lock->count) == -1) > return 0; >
One concern I have is this change will eliminate any optimistic spinning as long as there is a waiter. Is there a middle ground that we can allow only one spinner if there are waiters? In other words, we allow spinning when atomic_read(&lock->count) == -1 but there is no one on the osq lock that queue up the spinners (i.e. no other process doing optimistic spinning). This could allow a bit of spinning without starving out the waiters. Tim
