linux-kernel - Re: [PATCH 2/3] x86/topology: Fix AMD core count

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Date:	Mon, 21 Mar 2016 18:05:16 +0800
From:	Huang Rui <ray.huang@....com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Sherry Hurwitz <sherry.hurwitz@....com>,
	Peter Zijlstra <peterz@...radead.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
	<aherrmann@...e.com>, <jencce.kernel@...il.com>,
	"Gang Long" <gang.long@....com>
Subject: Re: [PATCH 2/3] x86/topology: Fix AMD core count

On Mon, Mar 21, 2016 at 09:23:41AM +0100, Borislav Petkov wrote:
> On Mon, Mar 21, 2016 at 11:07:46AM +0800, Huang Rui wrote:
> > OK, we will find some fam15h, fam16h platforms to verify it. Please
> > wait for my feedback.
> > 
> > But I am confused with c->x86_max_cores /= smp_num_siblings, what is
> > the real meaning of c->x86_max_cores here for AMD, the whole compute
> > unit numbers per socket?
> 
> Yes, it is the cores and each core can contain two or more logical
> threads. In AMD speak, that's the compute unit count. We read it in
> detect_ht() from CPUID(1).EBX[23:16] which is LogicalProcessorCount,
> i.e., CPUID(8000_0008).ECX[NC] + 1, i.e., the number of cores. And
> "cores" in BKDG speak is the number of all cores in a processor which
> are distributed across compute units....
> 
> That's why we divide by the number of siblings, i.e., the number of
> cores in a CU, in AMD speak.
> 
> I know, it is confusing but once we're fine with the nomenclature, it'll
> become as clear as day. :-)
> 

OK, actually, there was a topology bug on Carrzio before, the thread
number was detected as 1:

Before:

autotest@...otest-Gardenia88:~$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    1
Core(s) per socket:    4
Socket(s):             1
NUMA node(s):          1
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 96
Model name:            AMD Eng Sample: ZM1810C1Y4381_34/18/12/06_9874
Stepping:              0
CPU MHz:               1400.000
CPU max MHz:           1800.0000
CPU min MHz:           1400.0000
BogoMIPS:              3592.19
Virtualization:        AMD-V
L1d cache:             32K
L1i cache:             64K
L2 cache:              1024K
NUMA node0 CPU(s):     0-3


Now:

ray@...ub:~/tip$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                4
On-line CPU(s) list:   0-3
Thread(s) per core:    2
Core(s) per socket:    2
Socket(s):             1
NUMA node(s):          1
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 96
Stepping:              0
CPU MHz:               1400.000
BogoMIPS:              3592.19
Virtualization:        AMD-V
L1d cache:             32K
L1i cache:             96K
L2 cache:              1024K
NUMA node0 CPU(s):     0-3

Looks better. I will test it on fam16h machine tomorrow, if it's OK,
will add my Test-by.

Thanks,
Rui