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    SubjectRe: Linux 2.6.21-rc1
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    On Wed, 2007-02-21 at 19:18 +0100, Thomas Gleixner wrote:
    > On Wed, 2007-02-21 at 09:38 -0800, Daniel Walker wrote:
    > > > >
    > > > > Could be the switch over then which confuses the NMI .
    > > >
    > > > Why? The switch just stops the PIT/HPET. It does not fiddle with IO_APIC
    > > > and friends at all.
    > >
    > > I'm not an expert on the io-apic, but the check_timer() function seemed
    > > to assume IRQ0 was happening regularly ..
    >
    > Again:
    >
    > check_timer() is called _BEFORE_ we even touch the local APIC timers. At
    > this point PIT/HPET _IS_ firing IRQ0 with HZ frequency.

    Right, but eventually there isn't a regular timer interrupt through the
    io-apic. I don't think in the past IRQ0 stops without the system
    crashing, so check_timer() could assume the timer (IRQ0) is _always_
    regular.

    do you know what the requirement are for routing the NMI through the
    io-apic?

    > > Well, I'm pretty sure it's HRT, cause in prior versions this only
    > > happened when HRT is enabled. Then you guys went to the lapic all the
    > > time, and now this is happening all the time ..
    >
    > The NMI is stuck:
    >
    > if (nmi_count(cpu) - prev_nmi_count[cpu] <= 5) {
    > printk("CPU#%d: NMI appears to be stuck (%d->%d)!\n",
    > cpu,
    > prev_nmi_count[cpu],
    > nmi_count(cpu));
    >
    > This has nothing to do with jiffies.

    I think it has to do with IRQ0 . Did I mention this doesn't happen in
    2.6.20 .

    > There have been a bunch of changes in arch/i386/kernel/nmi.c as well.
    >
    > > You can't reproduce this?
    >
    > Nope.

    Do you use nmi_watchdog=1 ?

    Daniel

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