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    SubjectRe: [PATCH V7 2/4 net-next] skbuff: Add userspace zero-copy buffers in skb
    From
    From: Shirley Ma <mashirle@us.ibm.com>
    Date: Tue, 28 Jun 2011 09:51:32 -0700

    > On Mon, 2011-06-27 at 15:54 -0700, David Miller wrote:
    >> From: Shirley Ma <mashirle@us.ibm.com>
    >> Date: Mon, 27 Jun 2011 08:45:10 -0700
    >>
    >> > To support skb zero-copy, a pointer is needed to add to skb share
    >> info.
    >> > Do you agree with this approach? If not, do you have any other
    >> > suggestions?
    >>
    >> I really can't form an opinion unless I am shown the complete
    >> implementation, what this give us in return, what the impact is, etc.
    ..
    > You can see the overall CPU saved 50% w/i zero-copy.
    >
    > The impact is every skb allocation consumed one more pointer in skb
    > share info, and a pointer check in skb release when last reference is
    > gone.
    >
    > For skb clone, skb expand private head and skb copy, it still keeps copy
    > the buffers to kernel, so we can avoid user application, like tcpdump to
    > hold the user-space buffers too long.

    Ok, now show me the "complete implementation". I'm as interested in
    the code as I am in the numbers, that's why I asked for both.


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