Messages in this thread | | | Date | Thu, 8 May 2014 21:12:28 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v10 10/19] qspinlock, x86: Allow unfair spinlock in a virtual guest |
| |
On Wed, May 07, 2014 at 11:01:38AM -0400, Waiman Long wrote:
No, we want the unfair thing for VIRT, not PARAVIRT.
> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 9e7659e..10e87e1 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -227,6 +227,14 @@ static __always_inline int get_qlock(struct qspinlock *lock) > { > struct __qspinlock *l = (void *)lock; > > +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS > + if (static_key_false(¶virt_unfairlocks_enabled)) > + /* > + * Need to use atomic operation to get the lock when > + * lock stealing can happen. > + */ > + return cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0;
That's missing {}.
> +#endif
> barrier(); > ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL; > barrier();
But no, what you want is:
static __always_inline bool virt_lock(struct qspinlock *lock) { #ifdef CONFIG_VIRT_MUCK if (static_key_false(&virt_unfairlocks_enabled)) { while (!queue_spin_trylock(lock)) cpu_relax();
return true; } #else return false; }
void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) { if (virt_lock(lock)) return;
... }
| |