AMD Zen 4 SMBA & BMEC Features Still Working Their Way To The Linux Kernel

Written by Michael Larabel in AMD on 22 January 2023 at 06:25 AM EST. Add A Comment
Two quality of service features new with the Zen 4 processors are still seeing their software support squared away ahead of mainlining in the Linux kernel.

Going back to August even before AMD formally announced any Zen 4 processors, AMD Linux engineers began posting patches for Slow Memory Bandwidth Configuration (L3SBE / SMBA) and Bandwidth Monitoring Event Configuration (BMEC) as new QoS features. 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. The SMBA functionality in particular should be useful for CXL memory.

Recently AMD engineers sent out their eleventh spin of these SMBA and BMEC patches for the Linux kernel. These QoS features are still being refined with comments from upstream code reviews as well as re-basing the patches each time.

With the v11 patches sent out earlier this month it looks like work is slowly winding down on enabling these new QoS features that will be useful with the new AMD 4th Gen EPYC "Genoa" processors.

We'll see if this feature work is all squared away in time for the Linux 6.3 kernel series kicking off in mid-February but otherwise those with AMD's new platform and looking to make use of these QoS Features can find the v11 patches on the kernel mailing list. At least AMD got these patches out ahead of the Zen 4 launch but due to the number of rounds of review/revisions and the like it's taking several months until post-launch for the functionality to be supported by a released kernel. If the patches make it for v6.3, that stable kernel should be out around the end of April.
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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via

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