AMD Slow Memory Bandwidth Allocation Enforcement Ready For Linux 6.3

AMD Slow Memory Bandwidth Allocation Enforcement as a new feature found with AMD EPYC 9004 series processors will be supported by the in-development Linux 6.3 kernel.

Going back to last August AMD engineers began sending out Linux patches for this Slow Memory Bandwidth Allocation feature referred to as SMBA or also as L3SBE. 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.

"With this feature, the QOS enforcement policies can be applied to the external slow memory connected to the host. QOS enforcement is accomplished by assigning a Class Of Service (COS) to a processor and specifying allocations or limits for that COS for each resource to be allocated."

This Slow Memory Bandwidth Allocation Enforcement functionality is being wired up into the Linux kernel's x86 resource control "resctrl" code for dealing with Compute Express Link (CXL) devices, accelerators, and other classes of slower memory. The functionality is further outlined within AMD's QoS extensions documentation.

Slow Memory Bandwidth Allocation is supported by AMD Zen 4 server processors that have been shipping since the end of last year with the EPYC 9004 series. It's unfortunate that it's taken months into post-launch period for this QoS feature to be mainlined to the Linux kernel, which will reach stable with v6.3 in April, but at least it's here now and ahead of more CXL memory devices and accelerators reaching the data center.