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    SubjectRe: TCP Segmentation Offloading (TSO)
    David S. Miller writes:

    > It is real requirement, x86 works because unaligned
    > access is handled transparently by cpu.
    > But on every non-x86 csum_partial I have examined, worse than
    > 2-byte aligned data start is totally not handled. It is not difficult
    > to figure out why this is the case, everyone has copied by example. :-)

    PPC and PPC64 are OK, I believe, since the CPU handles (almost) all
    unaligned accesses in hardware. (Some PowerPC implementations trap if
    the access crosses a page boundary but the newer ones even handle that
    case in hardware, and if we do get the trap we fix it up.)

    I notice though that if the length is odd, we (PPC) put the last byte
    in the left-hand (most significant) byte of a 16-bit halfword, with
    zero in the other byte, and add it in, whereas i386 puts the last byte
    in the least-significant position. Hmmm... should be OK though since
    I presume the result will be reduced and then converted to network
    byte order before being put in the packet. And since there is an
    end-around carry we should end up with the same bytes that i386 does.

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      Last update: 2005-03-22 13:28    [W:0.022 / U:2.700 seconds]
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