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    Subject[PATCH] x86: put trigger in to detect mismatched apic versions.
    Ingo Molnar wrote:
    > * Mike Travis <travis@sgi.com> wrote:
    >
    >> Hi Ingo,
    >>
    >> I did notice that the versions all came up the same, and that the checks
    >> were very specific. I was trying to be as transparent and unintrusive
    >> as possible. Since there's so few calls, I though this was a good
    >> approach but apparently I was wrong.
    >>
    >> I like the idea of collapsing the array down to one and checking to see
    >> if all apic's have the same version, but is this really the case? Must
    >> all apics be the same?
    >
    > Could you please send a patch that doesnt change the code, only adds a
    > 'boot APIC version' kind of variable as an apic_version __read_mostly
    > variable and does a WARN_ONCE() if that mismatches? We can then stick that
    > into -tip and see whether it triggers.
    >
    > The max array size is ~128K, right? So if the WARN_ONCE() does not
    > trigger, we can just drop the array and use the central apic_version
    > variable ...
    >
    > And even if it _does_ trigger, the version incompatibilities between APIC
    > protocols are very rare. They only happen across wildly different CPU
    > architectures like when going from very old external apics to integrated
    > apics, or going from apics to x-apics. We wont see any mixing across those
    > boundaries.
    >
    > Ingo

    Btw, I checked with our UV architect and the problem is that we need a
    16 bit apic id which is what caused the MAX_APICS to be bumped to 32k.
    The lower 8 bits are the normal apic id, and the upper bit relate to
    the node. This means cpu 0 on node 0 has the same apic id as cpu 0 on
    node 1, etc. I also asked about whether we could rely on always having
    the same apic version, and the answer was yes, though it's really only
    relevant between the cpus on a node.

    Thanks,
    Mike
    ---
    Subject: x86: put trigger in to detect mismatched apic versions.

    Fire off one message if two apic's discovered with different
    apic versions.

    Signed-off-by: Mike Travis <travis@sgi.com>
    ---
    arch/x86/kernel/apic.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- linux-2.6-for-ingo.orig/arch/x86/kernel/apic.c
    +++ linux-2.6-for-ingo/arch/x86/kernel/apic.c
    @@ -1833,6 +1833,11 @@ void __cpuinit generic_processor_info(in
    num_processors++;
    cpu = cpumask_next_zero(-1, cpu_present_mask);

    + if (version != apic_version[boot_cpu_physical_apicid])
    + WARN_ONCE(1,
    + "ACPI: apic version mismatch, bootcpu: %x cpu %d: %x\n",
    + apic_version[boot_cpu_physical_apicid], cpu, version);
    +
    physid_set(apicid, phys_cpu_present_map);
    if (apicid == boot_cpu_physical_apicid) {
    /*


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