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Date:   Fri, 16 Jun 2023 10:16:51 -0400
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Cc:     yazen.ghannam@amd.com,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
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Subject: Re: [PATCH] x86/mce: Schedule mce_setup() on correct CPU for CPER
 decoding
Content-Language: en-US
To:     "Luck, Tony" <tony.luck@intel.com>, Borislav Petkov <bp@alien8.de>
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From:   Yazen Ghannam <yazen.ghannam@amd.com>
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On 6/15/2023 1:54 PM, Luck, Tony wrote:
>>          for_each_possible_cpu(cpu) {
>>                  if (cpu_data(cpu).initial_apicid == lapic_id) {
>>                          m.extcpu = cpu;
> 
> Are there any other places in the kernel where we need to find the
> Linux CPU number starting from the apic id?
> 
> I briefly looked a while back when I needed this for some
> debug use case and didn't find it then. But Linux changes
> and maybe there are some now.
> 
> Which is a long way to say I'd like to see boot code initialize an array so the above
> could just be:
> 
> 	m.extcpu = lapic_to_cpu[lapic_id];
>

So functionally the inverse of "x86_cpu_to_apicid", right? Though not 
per_cpu, of course.

I'll try and write this up if I don't find anything like it.

> But we'd need at least a couple of use cases to justify.
> 

Can you describe your original use case?

Thanks,
Yazen