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    SubjectRe: Is sendfile all that sexy?


    On Sun, 14 Jan 2001, Ingo Molnar wrote:

    >
    > i believe what you are seeing here is the overhead of the pagecache. When
    > using sendmsg() only, you do not read() the file every time, right? Is

    In that case just a user space buffer is sent i.e no file association.

    > ttcp using multiple threads?

    Only a single thread, single flow setup. Very primitive but simple.

    > In that case if the sendfile() is using the
    > *same* file all the time, creating SMP locking overhead.
    >
    > if this is the case, what result do you get if you use a separate,
    > isolated file per process? (And i bet that with DaveM's pagecache
    > scalability patch the situation would also get much better - the global
    > pagecache_lock hurts.)
    >

    Already doing the single file, single process. However, i do run by time
    which means i could read the file from the begining(offset 0) to the end
    then re-do it for as many times as 15secs would allow. Does this affect
    it? I tried one 1.5 GB file, it was oopsing and given my setup right now i
    cant trace it. So i am using about 170M which is read about 8 times in
    the 15 secs

    cheers,
    jamal

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