Re: sem_lock() vs qspinlocks

[Waiman Long]

On 05/20/2016 11:00 AM, Davidlohr Bueso wrote:
> On Fri, 20 May 2016, Peter Zijlstra wrote:
>
> > On Thu, May 19, 2016 at 10:39:26PM -0700, Davidlohr Bueso wrote:
> > >  In addition, this makes me wonder if queued_spin_is_locked() should 
> > > then be:
> > >
> > > -    return atomic_read(&lock->val);
> > > +    return atomic_read(&lock->val) & _Q_LOCKED_MASK;
> > >
> > > And avoid considering pending waiters as locked.
> >
> > Probably
>
> 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);
>
> Thanks,
> Davidlohr

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

Cheers,
Longman