linux-kernel - Re: [RFC PATCH] x86/cpu/hygon: Fix phys_proc_id calculation logic for multi-die processor

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Date:   Sat, 23 Mar 2019 18:56:52 +0800
From:   Pu Wen <puwen@...on.cn>
To:     Borislav Petkov <bp@...en8.de>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/cpu/hygon: Fix phys_proc_id calculation logic for
 multi-die processor

On 2019/3/23 16:59, Borislav Petkov wrote:
> On Sat, Mar 23, 2019 at 10:13:39AM +0800, Pu Wen wrote:
>> Current physical id is computed via "phys_proc_id = initial_apicid >>
>> bits".
>>
>> For 4-Die 2 socket system, the physical id of socket 2 is:
>> initial_apicid >> bits = 0b1xxxxxx >> 6 = 1.
>> The result is true.
>>
>> But for 2-Die 2 socket system, the physical id of socket 2 is:
>> initial_apicid >> bits = 0b10xxxxx >> 5 = 2,
>> and for 1-Die 2 socket system, the physical id of socket 2 is:
>> initial_apicid >> bits = 0b100xxxx >> 4 = 4.
>> The results are not correct any more.
>>
>> So the adjustment for the 1-Die/2-Die 2 socket system is needed.
>> And just use ApicId[6], which already defined the right thing, as the
>> socket ID.
> 
> I understand all that. But let me repeat my question:
> 
> So why do you need to do something different than what AMD does?
> 
> You said you're programming the initial APIC ID the same as AMD. So why
> doesn't this need to be changed in AMD code too but only for hygon?

Because AMD doesn't have 2-Socket system with 1-Die/2-Die processors(see
reference [2]). So it will return the right result when getting physical
ID in AMD system.

[2] https://www.amd.com/en/products/specifications/processors

-- 
Regards,
Pu Wen