Re: TCP transmit performance regression

Eric Dumazet
2012-07-05T09:49:25Z

On Thu, 2012-07-05 at 16:42 +0800, Ming Lei wrote:
> On Thu, Jul 5, 2012 at 4:33 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > On Thu, 2012-07-05 at 16:27 +0800, Ming Lei wrote:
> >
> >> After some investigation, the problem is caused by enabling
> >> DEBUG_SLAB, so it is not a regression.
> >>
> >
> > Strange, unless your machine is a _very_ slow one maybe ?
>
> It is a beagle-xm board, and its cpu is ARMv7, 1GHz.

OK, driver seems buggy, please try following patch (on both sides if
possible)

drivers/net/usb/smsc95xx.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index b1112e7..0a4ae35 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -1084,26 +1084,23 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
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_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);
}