ax88179_178a: avoid copy of tx tcp packets

ax88179_tx_fixup() has quite complex code trying to push 8 bytes
of control data (len/mss), but fails to do it properly for TCP packets,
incurring an extra copy and point of memory allocation failure.

Lets use the simple and approved way.

dev->needed_headroom being 8, all frames should have 8 bytes of
headroom, so the extra copy should be unlikely anyway.

This patch should improve performance for TCP xmits.

Reported-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 5a468f3..fb0caa2 100644 (file)
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1169,31 +1169,18 @@ ax88179_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
        int frame_size = dev->maxpacket;
        int mss = skb_shinfo(skb)->gso_size;
        int headroom;
-       int tailroom;
 
        tx_hdr1 = skb->len;
        tx_hdr2 = mss;
        if (((skb->len + 8) % frame_size) == 0)
                tx_hdr2 |= 0x80008000;  /* Enable padding */
 
-       headroom = skb_headroom(skb);
-       tailroom = skb_tailroom(skb);
+       headroom = skb_headroom(skb) - 8;
 
-       if (!skb_header_cloned(skb) &&
-           !skb_cloned(skb) &&
-           (headroom + tailroom) >= 8) {
-               if (headroom < 8) {
-                       skb->data = memmove(skb->head + 8, skb->data, skb->len);
-                       skb_set_tail_pointer(skb, skb->len);
-               }
-       } else {
-               struct sk_buff *skb2;
-
-               skb2 = skb_copy_expand(skb, 8, 0, flags);
+       if ((skb_header_cloned(skb) || headroom < 0) &&
+           pskb_expand_head(skb, headroom < 0 ? 8 : 0, 0, GFP_ATOMIC)) {
                dev_kfree_skb_any(skb);
-               skb = skb2;
-               if (!skb)
-                       return NULL;
+               return NULL;
        }
 
        skb_push(skb, 4);