netdev - Re: [PATCH net-next] net: ftgmac100/ftmac100: dont pull too much data

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Date:	Thu, 12 Jul 2012 22:35:18 +0800
From:	Po-Yu Chuang <ratbert.chuang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Po-Yu Chuang <ratbert@...aday-tech.com>
Subject: Re: [PATCH net-next] net: ftgmac100/ftmac100: dont pull too much data

Thank you Eric. :-)

regards,
Po-Yu Chuang

On Thu, Jul 12, 2012 at 10:19 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> Drivers should pull only ethernet header from page frag
> to skb->head.
>
> Pulling 64 bytes is too much for TCP (without options) on IPv4.
>
> However, it makes sense to pull all the frame if it fits the
> 128 bytes bloc allocated for skb->head, to free one page per
> small incoming frame.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Po-Yu Chuang <ratbert@...aday-tech.com>
> ---
>  drivers/net/ethernet/faraday/ftgmac100.c |    9 +++++++--
>  drivers/net/ethernet/faraday/ftmac100.c  |   11 +++++++----
>  2 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
> index 16b0704..74d749e 100644
> --- a/drivers/net/ethernet/faraday/ftgmac100.c
> +++ b/drivers/net/ethernet/faraday/ftgmac100.c
> @@ -479,9 +479,14 @@ static bool ftgmac100_rx_packet(struct ftgmac100 *priv, int *processed)
>                 rxdes = ftgmac100_current_rxdes(priv);
>         } while (!done);
>
> -       if (skb->len <= 64)
> +       /* Small frames are copied into linear part of skb to free one page */
> +       if (skb->len <= 128) {
>                 skb->truesize -= PAGE_SIZE;
> -       __pskb_pull_tail(skb, min(skb->len, 64U));
> +               __pskb_pull_tail(skb, skb->len);
> +       } else {
> +               /* We pull the minimum amount into linear part */
> +               __pskb_pull_tail(skb, ETH_HLEN);
> +       }
>         skb->protocol = eth_type_trans(skb, netdev);
>
>         netdev->stats.rx_packets++;
> diff --git a/drivers/net/ethernet/faraday/ftmac100.c b/drivers/net/ethernet/faraday/ftmac100.c
> index 829b109..b901a01 100644
> --- a/drivers/net/ethernet/faraday/ftmac100.c
> +++ b/drivers/net/ethernet/faraday/ftmac100.c
> @@ -441,11 +441,14 @@ static bool ftmac100_rx_packet(struct ftmac100 *priv, int *processed)
>         skb->len += length;
>         skb->data_len += length;
>
> -       /* page might be freed in __pskb_pull_tail() */
> -       if (length > 64)
> +       if (length > 128) {
>                 skb->truesize += PAGE_SIZE;
> -       __pskb_pull_tail(skb, min(length, 64));
> -
> +               /* We pull the minimum amount into linear part */
> +               __pskb_pull_tail(skb, ETH_HLEN);
> +       } else {
> +               /* Small frames are copied into linear part to free one page */
> +               __pskb_pull_tail(skb, length);
> +       }
>         ftmac100_alloc_rx_page(priv, rxdes, GFP_ATOMIC);
>
>         ftmac100_rx_pointer_advance(priv);
>
>
> --
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