Proposed Linux Kernel Patch Could Boost Raspberry Pi 5 Performance by Up to 18 Percent

A new approach to memory access could bring big gains — but the road to upstream acceptance is a bumpy one.

Gareth Halfacree
20 days agoHW101

A proposed patch to the Linux kernel could boost performance on the Raspberry Pi 5 single-board computer by as much as 18 percent — by emulating non-uniform memory access (NUMA).

"This [patch] series adds a very simple NUMA emulation implementation and enables selecting it on arm64 platforms," Tvrtko Ursulin, who works at software consultancy and Raspberry Pi partner Igalia, explains in a mailing list message brought to our attention by Phoronix. "Obvious question is why? Short answer — it can bring a significant performance uplift on Raspberry Pi 5."

That performance uplift is relatively small but clearly measurable, at least in benchmarks: Ursulin claims that with the patch set added to the Linux kerne the Raspberry Pi 5 can boost its performance in the Geekbench 6 benchmark by around six percent in single-core mode, and by as much as 18 percent when using all four cores.

The secret: working around a lack support for non-uniform memory access (NUMA) capabilities in hardware through a software emulation approach. "Splitting the physical RAM into chunks," Ursulin explains, "and utilizing an allocation policy such as interleaving can enable the BCM2721 memory controller to better utilize parallelism in physical memory chip organization."

The path to have the code accepted upstream, so it becomes a standard feature of the Linux kernel, could be a long one, however. Linux maintainer Greg Kroah-Hartman responded to the patch proposal with the suggestion to "properly describe the NUMA topology in your bootloader" instead — and stated that "you are now asking me to maintain these new files, [and that's] not something I'm comfortable doing at all sorry."

Interested parties can find the discussion on the Linux kernel mailing list — and the truly committed can add the patches and compile the kernel to test the performance gain out for themselves.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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