netdev - Re: TCP transmit performance regression

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Date:	Thu, 05 Jul 2012 16:56:36 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: TCP transmit performance regression

On Thu, 2012-07-05 at 22:01 +0800, Ming Lei wrote:

> At default SMSC95xx turbo mode is true, rx buffer will be very big
> (17.5K). Or the large rx buffer size puts limit on concurrent URBs/SKBs
> count.  Both two may cause the problem.

I see. So we should try to recycle these large rx buffers in usbnet
instead of allocating/freeing them for each incoming packet.

Following patch does the copybreak of all incoming frames.

It has nice property of not lying anymore on skb truesize ;)

It should be applied on both sender and receiver

 drivers/net/usb/smsc95xx.c |   19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index b1112e7..3d9566f 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1080,30 +1080,17 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 				return 0;
 			}
 
-			/* last frame in this batch */
-			if (skb->len == size) {
-				if (dev->net->features & NETIF_F_RXCSUM)
-					smsc95xx_rx_csum_offload(skb);
-				skb_trim(skb, skb->len - 4); /* remove fcs */
-				skb->truesize = size + sizeof(struct sk_buff);
-
-				return 1;
-			}
-
-			ax_skb = skb_clone(skb, GFP_ATOMIC);
+			ax_skb = netdev_alloc_skb_ip_align(dev->net, size);
 			if (unlikely(!ax_skb)) {
 				netdev_warn(dev->net, "Error allocating skb\n");
 				return 0;
 			}
 
-			ax_skb->len = size;
-			ax_skb->data = packet;
-			skb_set_tail_pointer(ax_skb, size);
+			memcpy(skb_put(ax_skb, size), packet, size);
 
 			if (dev->net->features & NETIF_F_RXCSUM)
 				smsc95xx_rx_csum_offload(ax_skb);
-			skb_trim(ax_skb, ax_skb->len - 4); /* remove fcs */
-			ax_skb->truesize = size + sizeof(struct sk_buff);
+			__skb_trim(ax_skb, ax_skb->len - 4); /* remove fcs */
 
 			usbnet_skb_return(dev, ax_skb);
 		}


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