[PATCH] x86: put trigger in to detect mismatched apic versions.

From: Mike Travis
Date: Fri Jan 16 2009 - 18:22:32 EST

Ingo Molnar wrote:
> * Mike Travis <travis@xxxxxxx> 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.

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@xxxxxxx>
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
cpu = cpumask_next_zero(-1, cpu_present_mask);

+ if (version != apic_version[boot_cpu_physical_apicid])
+ "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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