Messages in this thread | | | Date | Mon, 19 May 2014 16:30:22 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v10 10/19] qspinlock, x86: Allow unfair spinlock in a virtual guest |
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On 05/08/2014 03:12 PM, Peter Zijlstra wrote: > On Wed, May 07, 2014 at 11:01:38AM -0400, Waiman Long wrote: > > > No, we want the unfair thing for VIRT, not PARAVIRT. >
Yes, you are right. I will change that to VIRT.
>> 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 {}.
It is a single statement which doesn't need braces according to kernel coding style. I could move the comments up a bit to make it easier to read.
>> +#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; > > ... > }
This is a possible way of doing it. I can do that in the patch series to simplify it. Hopefully that will speed up the review process and get it done quicker.
-Longman
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