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    SubjectRe: New net features for added performance
    Andi Kleen wrote:
    >
    > Jeff Garzik <jgarzik@mandrakesoft.com> writes:
    >
    > > Advantages: A de-allocation immediately followed by a reallocation is
    > > eliminated, less L1 cache pollution during interrupt handling.
    > > Potentially less DMA traffic between card and host.
    > >
    > > Disadvantages?
    >
    > You need a new mechanism to cope with low memory situations because the
    > drivers can tie up quite a bit of memory (in fact you gave up unified
    > memory management).

    I think you misunderstand.. netif_rx frees the skb. In this example:

    netif_rx(skb); /* free skb of size PKT_BUF_SZ */
    skb = dev_alloc_skb(PKT_BUF_SZ)

    an alloc of a PKT_BUF_SZ'd skb immediately follows a free of a
    same-sized skb. 100% of the time.

    It seems an obvious shortcut to me, to have __netif_rx or similar
    -clear- the skb head not free it. No changes to memory management or
    additional low memory situations created by this, AFAICS.


    > 4) Better support for aligned RX by only copying the header, no the whole
    > packet, to end up with an aligned IP header. Unless the driver knows about
    > all protocol lengths this means the stack needs to support "parse header
    > in this buffer, then switch to other buffer with computed offset for data"

    This requires scatter-gather hardware support, right? If so, would this
    support only exist for checksumming hardware -- like the current
    zerocopy -- or would non-checksumming SG hardware like tulip be
    supported too?

    Jeff


    --
    Jeff Garzik | "You see, in this world there's two kinds of
    Building 1024 | people, my friend: Those with loaded guns
    MandrakeSoft | and those who dig. You dig." --Blondie
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