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Why does Linux run so well on ARM
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this post was submitted on 20 Aug 2023
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I mean… On Linux you’re going to be running a bunch of open source applications that have been compiled for ARM specifically. A huge problem with Windows on ARM is going to be running legacy x86 / x86_64 applications. You’re probably not contending with this problem at all on Linux, and I suspect if you were you would be similarly unimpressed (you can get Linux to transparently execute executables for different platforms using binfmt_misc and qemu but it’s slooooooow).
Honestly the better question might be why the Mac transition to Apple silicon has been so smooth. Part of this is that Apple cares a lot less about keeping legacy software working and companies will make native versions of their software ASAP. But Apple also has a good translation layer with Rosetta for this, and has custom silicon (which Microsoft does not) and I would not be surprised if part of this custom silicon involves extended instructions which make running x86 applications more feasible, but I don’t know the details and this is just speculation on my part.
Apple designed the silicon to have an "x86 mode" for the memory model ordering, as well as an undocumented mode that makes certain arm instructions set flags similarly to x86. There's a good write up of the reasons here: https://dougallj.wordpress.com/2022/11/09/why-is-rosetta-2-fast/
Small correction: the flag setting modes aren't undocumented. They're standardized extensions. ARMv8.4 added
FEAT_FlagM, and ARMv8.5 addedFEAT_FlagM2.https://developer.arm.com/downloads/-/exploration-tools/feature-names-for-a-profile
IIRC, the only nonstandard ARM extension used by Rosetta 2 in Apple's processors is TSO, and that's also implemented by other manufacturers. It's also not a hard requirement to run
amd64under ARM. You can emulate it very slowly or restrict the application to a single core.Apologies for the tangent, but I needed to make sure nobody could defend Microsoft's prior failings by saying "but Apple has secret hardware sauce".
So while not technically "secret sauce," it's certainly "special sauce." Good point.