Re: TCP transmit performance regression

Eric Dumazet
2012-07-05T14:56:42Z

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);
}