On 15.11.2019 18:13, George Dunlap wrote:
On 11/15/19 5:06 PM, Andreas Kinzler wrote:
Hello All,
I compared the CPUID listings from Ryzen 2700X (attached as tar.xz) to
3700X and found only very few differences. I added
cpuid = [ "0x80000008:ecx=xxxxxxxxxxxxxxxx0100xxxxxxxxxxxx" ]
to xl.cfg and then Windows runs great with 16 vCPUs. Cinebench R15 score
is >2050 which is more or less the bare metal value.
Awesome. Any idea what those bits do?
From the AMD APM (https://www.amd.com/system/files/TechDocs/24594.pdf):
APIC ID size. The number of bits in the initial APIC20[ApicId] value
that indicate core ID within a processor. A zero value indicates that
legacy methods must be used to derive the maximum number of cores. The
size of this field determines the maximum number of cores (MNC) that the
processor could theoretically support, not the actual number of cores
that are actually implemented or enabled on the processor, as indicated
by CPUID Fn8000_0008_ECX[NC].
if (ApicIdCoreIdSize[3:0] == 0){
// Used by legacy dual-core/single-core processors
MNC = CPUID Fn8000_0008_ECX[NC] + 1;
} else {
// use ApicIdCoreIdSize[3:0] field
MNC = (2 ^ ApicIdCoreIdSize[3:0]);
}
The value programmed in 2700X is 4, on 3700X it is 7. See my dump in
https://lists.xenproject.org/archives/html/xen-devel/2019-09/msg02189.html
Please note that the value is an exponent - that means MNC is programmed
as 16 for 2700X and 128 for 3700X.
Regards Andreas
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