AMD Prepares Linux Support For L3SBE Slow Memory Bandwidth Configuration, BMEC

Some of the newest Linux patches out of AMD for new processors are implementing support for some recently-documented Quality of Service extensions: L3SBE and BMEC.

The new AMD Linux patches wire up the QoS extensions for Slow Memory Bandwidth Configuration (L3SBE) and Bandwidth Monitoring Event Configuration (BMEC). L3SBE for L3 External Slow Memory Bandwidth Allocation Enforcement allows for QoS enforcement policies to be applied to external slow memory connected to the host and specifying the allocations/limits for the class of service for each resource. BMEC allows for keeping a tally of all the total and local reads/writes and a variety of events like reads to memory in the local or non-local NUMA domains, dirty victims from the QoS domain, and more.

This patch series with nearly 500 lines of new code gets these new AMD QoS CPU features implemented in the x86/resctrl code. Given the timing though of these patches, these new QoS extensions aren't expected to be merged until at least the v6.1 cycle.

The presence of these features are checked by new CPU feature bits. The Linux kernel patches simply mention them as being found in "new" AMD processors, which more than likely is for next-generation EPYC Zen 4 processors. These features were documented earlier this year in the AMD QoS extension manual which given the timing of only going public with the feature details earlier this year is likely further indication of it being for Zen 4.