Date:	Fri, 16 Jan 2009 16:06:04 -0800
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: put trigger in to detect mismatched apic versions.

Mike Travis wrote:
> Ingo Molnar wrote:
>> * Mike Travis <travis@....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@....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) {
>  		/*

I've pushed this one to my-for-you git tree as well.

(Seems awful quiet ... is everyone heading to Australia? ;-)

Thanks,
Mike
-- -

The following changes since commit 6eb714c63ed5bd663627f7dda8c4d5258f3b64ef:
  Mike Travis (1):
        cpufreq: use work_on_cpu in acpi-cpufreq.c for drv_read and drv_write

are available in the git repository at:

  ssh://master.kernel.org/pub/scm/linux/kernel/git/travis/linux-2.6-cpus4096-for-ingo.git master

Mike Travis (1):
      x86: put trigger in to detect mismatched apic versions.

 arch/x86/kernel/apic.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)


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