[PATCH net-next] ax88179_178a: avoid copy of tx tcp packets

Eric Dumazet
2013-08-01T13:49:52Z

From: Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

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-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Tested-by: Ming Lei <ming.lei-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Signed-off-by: Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
---
drivers/net/usb/ax88179_178a.c | 21 ++++-----------------
1 file changed, 4 insertions(+), 17 deletions(-)

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 2bc87e3..e2120d6 100644
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1166,31 +1166,18 @@ 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;