Quote:AMD today quietly posted a new open-source Linux kernel driver for review... the AMD 3D V-Cache Performance Optimizer Driver. This AMD 3D V-Cache Performance Optimizer Driver for Linux is intended to help optimize performance on systems sporting 3D V-Cache such as the AMD Ryzen "X3D" parts and the EPYC "X" processors.

The AMD 3D V-Cache Performance Optimizer Driver provides an interface for user-space to indicate whether their workloads are more cache sensitive or prefer higher frequency operation. This interface sets a bias to alter the CPU core reordering depending upon whether you are desiring higher frequences or larger L3 cache usage for your application(s).

With this core reordering by the AMD 3D V-Cache Optimizer, in frequency mode the cores within the faster CCD are prioritized before the slower CCD. Meanwhile in the "cache mode" of operation, the cores within the large L3 cache CCD are prioritized.

For those that were hoping all future AMD 3D V-Cache processors would boast CCDs with all the same large L3 caches, the work on this driver now seems to indicate that this won't necessarily be the case. Given today is the first time this Linux driver has been publicly posted, it would seem that at least some future AMD processor models will continue with only a subset of the CCDs having the big cache sizes.

This new driver is gated by the new "AMD_3D_VCACHE" Kconfig option and the driver named x3d_vcache. When enabled and running on a AMD 3D V-Cache processor, the /sys/bus/platform/drivers/amd_x3d_vcache/AMDI0101:00/amd_x3d_mode sysfs file is exposed where users can write "frequency" for setting the high frequency preference or "cache" for preferring cores from the larger L3 CCD as a priority.

This new AMD 3D V-Cache Performance Optimizer driver for Linux is now out for review on the platform-driver-x86 mailing list. Hopefully it can get reviewed and queued up in time for the upcoming Linux v6.13 cycle.

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