Linux 6.10 To Correct The CCD/CCX Topology Information For Some AMD CPUs

Written by Michael Larabel in Linux Kernel on 1 April 2024 at 06:48 AM EDT. 1 Comment
A patch queued in TIP.git's "x86/cpu" branch for collecting ahead of the Linux 6.10 kernel cycle adds support for handling the AMD 0x80000026 leaf to correct CPU topology information reporting for some newer AMD processors.

The patch to the Linux kernel allows for making use of the extended CPUID leaf 0x80000026 for obtaining topology information that otherwise isn't available or correctly parsed from the CPUID leaf 0xb. In particular, the 0x80000026 leaf has the correct CCX and CCD die information on some newer processors. In turn this will ensure that Linux properly reports the correct die ID, logical die ID, max die per package, CPU dies, and the CPU die list.

AMD EPYC 9754 processors

The patch doesn't spell out which particular AMD CPUs need leaf 0x80000026 for the correct topology information but it does note a 4th Gen EPYC 128 core / 256 thread processor does need it for correct reporting. That is presumably the AMD EPYC 9754 "Bergamo" processor. The reporting difference demonstrated with the new code:

AMD reporting difference

More details on this AMD 0x80000026 leaf parsing via this patch. Again as it's now in TIP.git and by way of x86/cpu, this corrected AMD CPU topology information should be submitted for the next kernel cycle with Linux 6.10 as opposed to going into the "x86/fixes" that would mean for the current v6.9 cycle.
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