On Tue, Mar 21, 2023 at 6:33 PM Almudena Garcia <liberamenso10...@gmail.com> wrote: > > But how does a core know its CPU number? > > Calling cpu_number() function, or getting its APIC ID from its Local APIC
Ah. That's too hardware-y for me to understand; but I see that cpu_number () in i386/i386/cpu_number.c also uses apic, and apic_get_current_cpu () in i386/i386/apic.c looks fast enough, so, cool! I know that Linux uses %gs; in particular their docs say: -- >8 -- For example: DEFINE_PER_CPU(int, x); int z; z = this_cpu_read(x); results in a single instruction: mov ax, gs:[x] -- 8< -- https://docs.kernel.org/core-api/this_cpu_ops.html#inner-working-of-this-cpu-operations Sergey
