linux-kernel - Re: [PATCH ref0] net: add Faraday FTMAC100 10/100 Ethernet driver

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Date:	Fri, 25 Feb 2011 17:45:40 +0800
From:	Po-Yu Chuang <ratbert.chuang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	bhutchings@...arflare.com, joe@...ches.com, dilinger@...ued.net,
	mirqus@...il.com, davem@...emloft.net,
	Po-Yu Chuang <ratbert@...aday-tech.com>
Subject: Re: [PATCH ref0] net: add Faraday FTMAC100 10/100 Ethernet driver

Hi Eric,

On Fri, Feb 25, 2011 at 10:32 AM, Po-Yu Chuang <ratbert.chuang@...il.com> wrote:
> On Fri, Feb 25, 2011 at 1:48 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> Le jeudi 24 février 2011 à 18:39 +0100, Eric Dumazet a écrit :
>>> Le jeudi 24 février 2011 à 17:29 +0800, Po-Yu Chuang a écrit :
>>> > From: Po-Yu Chuang <ratbert@...aday-tech.com>
>>> > +
>>> > +static bool ftmac100_rx_packet(struct ftmac100 *priv, int *processed)
>>> > +{
>>> > +   struct net_device *netdev = priv->netdev;
>>> > +   struct ftmac100_rxdes *rxdes;
>>> > +   struct sk_buff *skb;
>>> > +   struct page *page;
>>> > +   dma_addr_t map;
>>> > +   int length;
>>> > +
>>> > +   rxdes = ftmac100_rx_locate_first_segment(priv);
>>> > +   if (!rxdes)
>>> > +           return false;
>>> > +
>>> > +   if (unlikely(ftmac100_rx_packet_error(priv, rxdes))) {
>>> > +           ftmac100_rx_drop_packet(priv);
>>> > +           return true;
>>> > +   }
>>> > +
>>> > +   /*
>>> > +    * It is impossible to get multi-segment packets
>>> > +    * because we always provide big enough receive buffers.
>>> > +    */
>>> > +   if (unlikely(!ftmac100_rxdes_last_segment(rxdes)))
>>> > +           BUG();
>>> > +
>>> > +   /* start processing */
>>> > +   skb = netdev_alloc_skb_ip_align(netdev, ETH_HLEN);
>>>
>>> Oh I see... You should allocate a bigger head (say... 128 bytes)
>>>
>>> And copy in it up to 128 bytes of first part... this to avoid upper
>>> stack to reallocate skb head (because IP/TCP processing need to get
>>> their headers in skb head)
>>
>> Take a look at drivers/net/niu.c :
>>
>> #define RX_SKB_ALLOC_SIZE   128 + NET_IP_ALIGN
>>
>> static int niu_process_rx_pkt(...)
>> {
>>        ...
>>        skb = netdev_alloc_skb(np->dev, RX_SKB_ALLOC_SIZE);
>>        ...
>>        while (1) {
>>                ...
>>                niu_rx_skb_append(skb, page, off, append_size);
>>        }
>> }
>
> Oh I got it.
>
> I will try this and redo the benchmarking.

It's a little faster than v5 now. Thanks.
I will submit the current version later.

One more question just curious, why 128 bytes?

best regards,
Po-Yu Chuang
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