[SCSI] fcoe: reduce contention for fcoe_rx_list lock [v2]

There is potentially lots of contention for the rx_list_lock.  On a cpu that is
receiving lots of fcoe traffic, the softirq context has to add and release the
lock for every frame it receives, as does the receiving per-cpu thread.  We can
reduce this contention somewhat by altering the per-cpu threads loop such that
when traffic is detected on the fcoe_rx_list, we splice it to a temporary list.
In this way, we can process multiple skbs while only having to acquire and
release the fcoe_rx_list lock once.

[ Braces around single statement while loop removed by Robert Love
  to satisfy checkpath.pl. ]

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>

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index d86ca37b3787b19667fbac7d973920cde6c214ea..58c88b0e87924d7c8371369cc8ef360dbe26dfbf 100644 (file)
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -1471,7 +1471,7 @@ static int fcoe_rcv(struct sk_buff *skb, struct net_device *netdev,
         * in softirq context.
         */
        __skb_queue_tail(&fps->fcoe_rx_list, skb);
-       if (fps->fcoe_rx_list.qlen == 1)
+       if (fps->thread->state == TASK_INTERRUPTIBLE)
                wake_up_process(fps->thread);
        spin_unlock(&fps->fcoe_rx_list.lock);
 
@@ -1790,23 +1790,29 @@ static int fcoe_percpu_receive_thread(void *arg)
 {
        struct fcoe_percpu_s *p = arg;
        struct sk_buff *skb;
+       struct sk_buff_head tmp;
+
+       skb_queue_head_init(&tmp);
 
        set_user_nice(current, -20);
 
        while (!kthread_should_stop()) {
 
                spin_lock_bh(&p->fcoe_rx_list.lock);
-               while ((skb = __skb_dequeue(&p->fcoe_rx_list)) == NULL) {
+               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)) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        spin_unlock_bh(&p->fcoe_rx_list.lock);
                        schedule();
                        set_current_state(TASK_RUNNING);
-                       if (kthread_should_stop())
-                               return 0;
-                       spin_lock_bh(&p->fcoe_rx_list.lock);
-               }
-               spin_unlock_bh(&p->fcoe_rx_list.lock);
-               fcoe_recv_frame(skb);
+               } else
+                       spin_unlock_bh(&p->fcoe_rx_list.lock);
        }
        return 0;
 }