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    SubjectRe: Intel P6 vs P7 system call performance
    Date
    In article <200212090830.gB98USW05593@flux.loup.net>,
    Mike Hayward <hayward@loup.net> wrote:
    >
    >I have been benchmarking Pentium 4 boxes against my Pentium III laptop
    >with the exact same kernel and executables as well as custom compiled
    >kernels. The Pentium III has a much lower clock rate and I have
    >noticed that system call performance (and hence io performance) is up
    >to an order of magnitude higher on my Pentium III laptop. 1k block IO
    >reads/writes are anemic on the Pentium 4, for example, so I'm trying
    >to figure out why and thought someone might have an idea.

    P4's really suck at system calls. A 2.8GHz P4 does a simple system call
    a lot _slower_ than a 500MHz PIII.

    The P4 has problems with some other things too, but the "int + iret"
    instruction combination is absolutely the worst I've seen. A 1.2GHz
    Athlon will be 5-10 times faster than the fastest P4 on system call
    overhead.

    HOWEVER, the P4 is really good at a lot of other things. On average, a
    P4 tends to perform quite well on most loads, and hyperthreading (if you
    have a Xeon or one of the newer desktop CPU's) also tends to work quite
    well to smooth things out in real life.

    In short: the P4 architecture excels at some things, and it sucks at
    others. It _mostly_ tends to excel more than suck.

    Linus
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