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    SubjectRe: Performance/Memory usage patch
       Date: 	Wed, 9 Apr 1997 10:29:05 +0100 (BST)
    From: Mark Hemment <>

    The figures under "lmbench" show limited/no improvement, but
    running other tests (such as a large number of kernel compiles) do
    show a performance increase (particularly on a 486 box).

    I believe networking throughput/latencies take a small performance
    hit. This is probably due to different byte alignments of
    dynamically allocated memory. I do not understand the networking
    code - perhaps somebody could try SLABising it (making sure common
    accessed members are on the same h/w cache line, and using

    I think I know what is behind all this. I see in your patch that you
    undo one of the arguments to the creation of the vm_area_struct SLAB
    cache, I put that there _specifically_ because if I did not the
    machine ran slow as balls. Investigation showed that I was _not_
    getting 8-byte alignment to the structure which is necessary to
    prevent _all_ accesses to the loff_t member from invoking unalignment
    traps on the Sparc.

    You will see this as an issue on any modern architecture.

    Kmalloc (sort of) guarenteed for the most part 8-byte alignment for
    blocks of memory it returned, at a minimum SLAB and things built upon
    it should do the same for the very reason described above.

    I believe this can account for the networking slowdowns, and in
    particular it may explain why the lmbench numbers were about the same
    otherwise ;-)

    If you dealt with this issue in your patch set (I've looked it over a
    few times but have not played actively with it yet) I apologize.

    Yow! 11.26 MB/s remote host TCP bandwidth & ////
    199 usec remote TCP latency over 100Mb/s ////
    ethernet. Beat that! ////
    -----------------------------------------////__________ o
    David S. Miller, /_____________/ / // /_/ ><

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