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    SubjectRe: libata/sata_nv latency on NVIDIA CK804 [was Re: AMD64 X2 lost ticks on PM timer]
    On Wed, Mar 22, 2006 at 05:09:08PM +0100, Andi Kleen wrote:
    > perfctr0 is already programmed. You can just use rdpmc on it
    >
    > Also my latest patchkit has a debugging patch for lost tries
    >
    > ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/lost-cli-debug

    Excellent.

    > Can you test it with this patch?

    I'll give it a try this evening; the test box is an
    FC5 upgrade guinea pig at the moment, and only half-migrated.

    > I'm still not quite convinced you're barking at the right tree
    > with these latency traces because it doesn't match the symptoms.

    Yes, I agree that that the latency issue is not due to the inb(),
    as I get lost ticks almost continuously at 1 KHZ, and the inb()-related
    latency occurs with much lower frequency.

    However, a 17ms inb() latency is rather dismal, and I need to
    address that hardware issue, perhaps by purchasing a 4-port card.

    I have not been chasing the other issue because the test box appears to
    keep perfect time with the -rt patch (on SMP) and NTP doesn't complain at
    all; I haven't yet had the chance to determine whether that is entirely
    due to John Stultz's new code, or if the preemption is responsible.

    -Bill

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