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    SubjectRe: Intel P6 vs P7 system call performance

    On Mon, 16 Dec 2002, Linus Torvalds wrote:
    > On my P4 machine, a "getppid()" is 641 cycles with sysenter/sysexit, and
    > something like 1761 cycles with the old "int 0x80/iret" approach. That's a
    > noticeable improvement, but I have to say that I'm a bit disappointed in
    > the P4 still, it shouldn't be even that much.

    On a slightly more real system call (gettimeofday - which actually matters
    in real life) the difference is still visible, but less so - because the
    system call itself takes more of the time, and the kernel entry overhead
    is thus not as clear.

    For gettimeofday(), the results on my P4 are:

    sysenter: 1280.425844 cycles
    int/iret: 2415.698224 cycles
    1135.272380 cycles diff
    factor 1.886637

    ie sysenter makes that system call almost twice as fast.

    It's not as good as a pure user-mode solution using tsc could be, but
    we've seen the kinds of complexities that has with multi-CPU systems, and
    they are so painful that I suspect the sysenter approach is a lot more
    palatable even if it doesn't allow for the absolute best theoretical


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