diff mbox

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

Message ID 1375364992.10515.141.camel@edumazet-glaptop
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet Aug. 1, 2013, 1:49 p.m. UTC 
From: Eric Dumazet <edumazet@google.com>

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>
---
 drivers/net/usb/ax88179_178a.c |   21 ++++-----------------
 1 file changed, 4 insertions(+), 17 deletions(-)



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Comments

Eric Dumazet Aug. 1, 2013, 1:52 p.m. UTC | #1 
On Thu, 2013-08-01 at 06:49 -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> 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.

I forgot to say this patch is for net-next, but depends on following fix
from net tree being applied.

commit 20f0170377264e8449b6987041f0bcc4d746d3ed
("usbnet: do not pretend to support SG/TSO")



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David Miller Aug. 4, 2013, 4:56 a.m. UTC | #2 
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 01 Aug 2013 06:52:45 -0700

> On Thu, 2013-08-01 at 06:49 -0700, Eric Dumazet wrote:
>> From: Eric Dumazet <edumazet@google.com>
>> 
>> 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.
> 
> I forgot to say this patch is for net-next, but depends on following fix
> from net tree being applied.
> 
> commit 20f0170377264e8449b6987041f0bcc4d746d3ed
> ("usbnet: do not pretend to support SG/TSO")

Thanks for letting me know.

Applied, thanks Eric.
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diff mbox

Patch

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;
-
-		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);