Re: sem_lock() vs qspinlocks

[Peter Zijlstra]

On Fri, May 20, 2016 at 04:47:43PM -0400, Waiman Long wrote:

> >Similarly, and I know you hate it, but afaict, then semantically
> >queued_spin_is_contended() ought to be:
> >
> >-       return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
> >+       return atomic_read(&lock->val);
> >

> Looking for contended lock, you need to consider the lock waiters also. So
> looking at the whole word is right.

No, you _only_ need to look at the lock waiters.