[SCSI] fcoe: Cleanup locking on fcoe_percpu_receive_thread

Noticed that we can shuffle the code around in fcoe_percpu_receive_thread a bit
and avoid taking the fcoe_rx_list lock twice per iteration.  This should improve
throughput somewhat.  With this change we take the lock, and check for new
frames in a single critical section.  Only if the list is empty do we drop the
lock and re-acquire it after being signaled to wake up.

Change Notes:
v2) did some further cleanup on the patch by replacing the 2nd call of
spin_lock/splice_init with a goto to the top of the outer loop.  This allows me
to change the inner while loop to an if conditional and remove the sencond check
of kthread_should_stop.  Based on suggestion from Vasu Dev.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/fcoe/fcoe.c

@@ -1851,23 +1851,25 @@ static int fcoe_percpu_receive_thread(void *arg)
 
 	set_user_nice(current, -20);
 
+retry:
 	while (!kthread_should_stop()) {
 
 		spin_lock_bh(&p->fcoe_rx_list.lock);
 		skb_queue_splice_init(&p->fcoe_rx_list, &tmp);
-		spin_unlock_bh(&p->fcoe_rx_list.lock);
-
-		while ((skb = __skb_dequeue(&tmp)) != NULL)
-			fcoe_recv_frame(skb);
 
-		spin_lock_bh(&p->fcoe_rx_list.lock);
-		if (!skb_queue_len(&p->fcoe_rx_list)) {
+		if (!skb_queue_len(&tmp)) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			spin_unlock_bh(&p->fcoe_rx_list.lock);
 			schedule();
 			set_current_state(TASK_RUNNING);
-		} else
-			spin_unlock_bh(&p->fcoe_rx_list.lock);
+			goto retry;
+		}
+
+		spin_unlock_bh(&p->fcoe_rx_list.lock);
+
+		while ((skb = __skb_dequeue(&tmp)) != NULL)
+			fcoe_recv_frame(skb);
+
 	}
 	return 0;
 }