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SubjectRe: Speed of memcpy, csum_partial and csum_partial_copy

>>>>> "me" == Pedro Roque Marques <roque@di.fc.ul.pt> writes:
>>>>> "Alan" == Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

Alan> There are three for TCP loopback unless someone has fiddled
Alan> recently. We copy:

sk_buff [with csum]
sk_buff to sk_buff
sk_buff-> user [skip csum]

Alan> While it seems a really dumb thing to do it makes sense as
Alan> there may be retransmissions and thus the receiver cannot go
Alan> using the queue pointers of the senders buffer copy. Its a
Alan> bad case solely applicable to loopback, and if we are going
Alan> to optimise loopback tcp we should do the solaris trick and
Alan> dump everything. In the mean time thats what AF_UNIX was
Alan> invented for.

me> On the TCP i've been seting up for 2.1 there is no need for
me> copy number 2 since the skb is cloned (the copy is restricted
me> to the skb header).

Well, i've been looking at the code and loopback does a clone of the
skb (the right thing to do) so there are really 2 data copies
only. There is the memcpy of the skb header but that does not seam
to show on Linus profile trace (it's 30-40 bytes for each 3k).

regards,
./Pedro.


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