[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>

1 files changed, 10 insertions, 8 deletions

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index 2b065d26a5ae..078d262ac7cc 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/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;
 }