> the linux kernel do not bother anymore and is compiled for "generic" x86_64 for instance, it is not worth it (and may cause more harm in the end) This is not

> the linux kernel do not bother anymore and is compiled for "generic" x86_64 for instance, it is not worth it (and may cause more harm in the end) This is not the reason why. Indeed x86_64 has a much broader instruction & register baseline than i386 did, so the impact of per-CPU tuning is less than it used to be. But even a generic compiled Linux selects CPU instruction sets at runtime for things like hardware-accelerated cryptography, because those instruction sets actually matter. If you have evidence that modern microcode magically recognizes hand-written AES and replaces it with the equivalent AES-NI instructions, please be sure to send Linus your patches with benchmarks.