On Fri, Sep 11, 2015 at 02:37:37PM -0400, Waiman Long wrote:
> This patch allows one attempt for the lock waiter to steal the lock
> when entering the PV slowpath. This helps to reduce the performance
> penalty caused by lock waiter preemption while not having much of
> the downsides of a real unfair lock.
> @@ -416,7 +414,8 @@ queue:
> * does not imply a full barrier.
> *
> */
If it really were once, like the Changelog says it is, then you could
have simply added:
if (pv_try_steal_lock(...))
goto release;
here, and not wrecked pv_wait_head() like you did. Note that if you do
it like this, you also do not need to play games with the hash, because
you'll never get into that situation.
> - pv_wait_head(lock, node);
> + if (pv_wait_head_and_lock(lock, node, tail))
> + goto release;
> while ((val = smp_load_acquire(&lock->val.counter)) &
> _Q_LOCKED_PENDING_MASK)
> cpu_relax();
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
