Linux

Yes, to use the CONFIG_X86_NATIVE_CPU option, you will need to compile the kernel yourself with this option enabled. This is a compile-time setting that affects how the compiler optimizes the build specifically for your system. Prebuilt kernels from distro repositories usually do not have this enabled, since they are built for broad compatibility with many different processors.

Yes, most likely need to compile it yourself. Or the distros would need a v1,v2,v3,v4 version. Also you need to know the feature set of you cpu. Distros will probably compile with the lowest common denominator, since those are compatible largest range of cpu's. Cachyos does compile it's packages for v3 optimization, I don't think that needs avx512. So can definitely see some distros trying something out.

This is a compile-time option that will tell the compiler to optimize for the CPU in your computer, rather than any CPU.

By default, the x86_64 kernel will build itself so that it can boot and run on any 64-bit Intel or AMD processor. This means it may have to ignore or check for newer instruction sets like (let’s say, totally at random) AVX512:

if (CPU supports AVX512)
    do_efficient_avx512_thing (a, b, c)
else
    a = something()
    b = some_nonavx512_prep_work()
    c = some_other_old_way_of_doing_things()
    do_nonavx512_thing (a, b, c)

So, if you have an AVX512-capable CPU, it still has to check before using that instruction. Plus, your compiled kernel will be slightly larger because it needs to contain both ways of doing the thing.

Using this option tells the compiler to compile code optimized for your current processor:

do_efficient_avx512_thing (a, b, c)

This is a gross oversimplication. The compiler will also take things into consideration such as instruction sets, scheduling, core and thread counts, big and small cores, and more.

But the tl;dr is that optimized code is smaller, faster, and maybe a teensy bit more power efficient.

The downside? If you try to boot this optimized code on an older CPU (or rarely, a newer CPU), it will eventually say “illegal instruction” and crash.

Any achievement requires sacrifice

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