On 11/18/19 12:54 PM, Jan Beulich wrote: > On 18.11.2019 12:39, 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. >> >> So this is setting those bits to 0100, or 4. > > One of the many possible problems with our incrementing of this field > could be that this results in a value that in "reserved" as per AMD's > documentation. At least for some of the Fam17 models they document > exactly which values are "legal".
Do you have a reference for this? I did manage to download one of the AMD manuals and find the reference for ecx:80000008, but it didn't mention any restrictions on legal values. At any rate, this will affect the topology calculation for Linux guests with more than 8 vcpus, so I don't think we can simply enable it across the board, even on the affected chipsets. If the xl.cfg cpuid override perists across migrate, documenting it might be the best solution for now. -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
