Messages in this thread | | | From | Po-Yu Chuang <> | Date | Thu, 24 Feb 2011 15:27:55 +0800 | Subject | Re: [PATCH v4] net: add Faraday FTMAC100 10/100 Ethernet driver |
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Hi David,
On Tue, Feb 1, 2011 at 12:35 PM, David Miller <davem@davemloft.net> wrote: > From: Po-Yu Chuang <ratbert.chuang@gmail.com> > Date: Tue, 1 Feb 2011 11:56:16 +0800 > >> If I simply allocate a page for each rx ring entry, I still need to allocate >> an skb and copy at least packet header in first page to skb->data. Then >> add the page of rest of payload to skb by skb_fill_page_desc(). > > You should attach the pages, the use __pskb_pull_tail() to bring in the > headers to the linear skb->data area. > > See drivers/net/niu.c:niu_process_rx_pkt().
I tried two ways to implement zero-copy. One is to preallocate skb big enough for any rx packet and use the skb as rx buffer. The other is use page as rx buffer, use skb_fill_page_desc() to add a data page to skb and then pull only header to skb by __pskb_pull_tail() as you suggested.
Two implementations are slower than the original memcpy version. (benchmarked with iperf)
I guess the problem is because a HW restriction that the rx buffer must be 64 bits aligned. Since I cannot make rx buffer starts at offset 2 bytes, the IP header, TCP header and data are not 4 bytes aligned. The performance drops drastically.
Therefore, I will submit later a v6 which is still using memcpy().
best regards, Po-Yu Chuang
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