netdev - Re: TCP transmit performance regression

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Date:	Fri, 6 Jul 2012 08:45:14 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: TCP transmit performance regression

On Thu, Jul 5, 2012 at 10:56 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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

In fact, I run the below command in the test beagle-xm box with SMSC95xx
NIC:

             iperf -c 192.168.0.103 -w 131072 -t 10

and run the below command in one x86 production machine(e1000e NIC)
running ubuntu 12.04:

            iperf -s -w 131072

The current problem is that the transmit performance on beagle-xm is
not good with the above iperf test if DEBUG_SLAB is enabled. But if
I set dev->rx_usb_size as 2048, the transmit performance can be
doubled, looks it is caused by the large rx buffer.

>
>  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);
>                 }
>
>

Unfortunately, the patch still hasn't any improvement on the transmit
performance of beagle-xm.

Thanks,
-- 
Ming Lei
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