On Wed, Apr 30, 2014 at 2:04 AM, Peter Zijlstra <pet...@infradead.org> wrote:
> On Mon, Apr 28, 2014 at 03:09:01PM -0700, Davidlohr Bueso wrote:
>> +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
>> +{
>> + int retval;
>
> And yet the return value is bool.
>
>> + struct task_struct *owner;
>> +
>> + rcu_read_lock();
>> + owner = ACCESS_ONCE(sem->owner);
>> +
>> + /* Spin only if active writer running */
>> + if (owner)
>> + retval = owner->on_cpu;
>> + else {
>> + /*
>> + * When the owner is not set, the sem owner may have just
>> + * acquired it and not set the owner yet, or the sem has
>> + * been released, or reader active.
>> + */
>> + retval = false;
>> + }
>
> And if you init the retval to false, you can leave this entire branch
> out.
>
>> + rcu_read_unlock();
>> +
>> + return retval;
>> +}
>
>
> Which yields the much shorter:
>
> static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
> {
> struct task_struct *owner;
> bool on_cpu = false;
Wouldn't we want to initialize on_cpu = true. For the !owner case, I
would expect that we want to spin for the lock.
> rcu_read_lock();
> owner = ACCESS_ONCE(sem->owner);
> if (owner)
> on_cpu = owner->on_cpu;
> rcu_read_unlock();
>
> return on_cpu;
> }
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