xen-netback: use skb to determine number of required guest Rx requests

Using the MTU or GSO size to determine the number of required guest Rx
requests for an skb was subtly broken since these value may change at
runtime.

After 1650d5455bd2dc6b5ee134bd6fc1a3236c266b5b (xen-netback: always
fully coalesce guest Rx packets) we always fully pack a packet into
its guest Rx slots.  Calculating the number of required slots from the
packet length is then easy.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 99a2dea50d5deff134b6c346f53a3ad1f583ee96)
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 3a44357f6c2619100f888919d334dbaf5da13f98..8ac916a5eda95217f6f5aff63715dd876d098fa2 100644 (file)
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -149,20 +149,19 @@ static inline pending_ring_idx_t pending_index(unsigned i)
        return i & (MAX_PENDING_REQS-1);
 }
 
-static int xenvif_rx_ring_slots_needed(struct xenvif *vif)
-{
-       if (vif->gso_mask)
-               return DIV_ROUND_UP(vif->dev->gso_max_size, XEN_PAGE_SIZE) + 1;
-       else
-               return DIV_ROUND_UP(vif->dev->mtu, XEN_PAGE_SIZE);
-}
-
 static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
 {
        RING_IDX prod, cons;
+       struct sk_buff *skb;
        int needed;
 
-       needed = xenvif_rx_ring_slots_needed(queue->vif);
+       skb = skb_peek(&queue->rx_queue);
+       if (!skb)
+               return false;
+
+       needed = DIV_ROUND_UP(skb->len, XEN_PAGE_SIZE);
+       if (skb_is_gso(skb))
+               needed++;
 
        do {
                prod = queue->rx.sring->req_prod;
@@ -2005,8 +2004,7 @@ static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
 
 static bool xenvif_have_rx_work(struct xenvif_queue *queue)
 {
-       return (!skb_queue_empty(&queue->rx_queue)
-               && xenvif_rx_ring_slots_available(queue))
+       return xenvif_rx_ring_slots_available(queue)
                || (queue->vif->stall_timeout &&
                    (xenvif_rx_queue_stalled(queue)
                     || xenvif_rx_queue_ready(queue)))