The Async Multiprocessing Has Sound Foundations in Linux, But Further Testing Is Needed

At the Embedded Linux Conference Europe 2026, Linux kernel developer Wolfram Sang examined the Linux building blocks for asymmetric multiprocessing (AMP). Sang concluded that they are robust enough to build upon, but acknowledged the need for additional testing due to thin contributor coverage and fragmented testing. His presentation centered on the Linux side of AMP systems, which consist of application CPUs and a smaller real-time core within the same system-on-chip.

Communication between these components is typically facilitated through mailboxes, shared SRAM or DDR, or more complex arrangements like SCMI for resource coordination. Sang highlighted the SCMI mechanism for communicating with dedicated system-control processors about resources like clocks, noting the added complexity of bidirectional communication requiring more mailboxes.

He also discussed how firmware can impose different communication arrangements, such as using two unidirectional mailboxes for bidirectional SCMI communication, creating challenges in acknowledgment paths. The talk also addressed other layers like remoteproc, which loads firmware and manages remote cores, and Virtio, which defines an open communication standard using shared-memory virtqueues.

Sang noted that while the number of commits for the remoteproc core has significantly increased over the years, the growth in driver contributions has slowed. Hardware spinlocks, despite showing a modest increase in commits, exhibit a relatively flat driver count. Sang emphasized the importance of increasing the number of reviewers and testers for these AMP components, citing the maintenance burden of seemingly minor changes and compatibility issues with firmware and U-Boot.

He highlighted that while OpenAMP provides build instructions and test cases, these examples are not uniformly compatible across all supported boards.