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    SubjectRe: SMP broken on pre-ACPI machine.
    On Thu, Oct 19, 2006 at 01:33:40AM -0400, Len Brown wrote:
    > On Wednesday 18 October 2006 18:24, Dave Jones wrote:
    > > I've been chasing a bug that got filed against the Fedora kernel
    > > a while back:
    > > This is a dual pentium pro from an era before we had ACPI, and
    > > it seems to be falling foul of this test in smpboot.c ..
    > >
    > > if (!smp_found_config && !acpi_lapic) {
    > > printk(KERN_NOTICE "SMP motherboard not detected.\n");
    > >
    > > My initial reaction is that the !acpi_lapic test should be conditional
    > > on some variable that gets set if the ACPI parsing actually succeeded.
    > acpi_lapic isn't related to the problem at hand -- that smp_found_config is not set.

    Right, it just seemed odd to me when I was eyeballing this code.

    > That said, allowing acpi_lapic=1 to bail out of this check has the sole
    > function of allowing SMP/PIC configurations. (smp_found_config
    > in ACPI mode is set if acpi_lapic and acpi_ioapic are set)
    > SMP/PIC configurations are not very interesting, except for debugging.
    > Indeed, MPS prohibits them by mandating an IOAPIC be present for SMP --
    > but ACPI has no such rule.

    Why smp_found_config isn't set in that guys configuration is a mystery to me,
    as his MPS tables look sane..

    MP Table:
    # APIC ID Version State Family Model Step Flags
    # 0 0x10 BSP, usable 6 2 1 0x0381
    # 0 0x10 AP, usable 6 1 7 0xfbff

    Hmm, wait, he has unpaired CPUs. I wonder if that's the reason.
    I know *some* combinations of PPro's are valid to be paired, but I'll
    need to dig out the old docs to be sure.


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