Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 10 Oct 2022 20:19:43 -0700 | Subject | Re: [GIT PULL] bitmap changes for v6.0-rc1 |
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On Mon, Oct 10, 2022 at 8:09 PM Yury Norov <yury.norov@gmail.com> wrote: > > > So I _think_ all the nr_cpu_id's games are mainly because we don't > > want to allocate huge arrays when you can't actually have that many > > CPU's - but for a small NR_CPUS situation that just isn't an issue > > anyway. > > > > Yes? No? > > You're talking about .data section. FORCE_NR_CPUS is about .text and > code generation.
No, it's more than just code size that you compare.
It's also the "walk over big arrays".
It doesn't matter if the *code* is simpler, if it's a fixed walk over 64 long-words because the code uses a fixed 4096-bit bitmap.
Yes, that constant 64 is simpler than loading a variable, but it's not *better*. It's worse. It has allocated more memory, and then it wastes time walking over it.
So just looking at code size and "simplicity" is bogus.
Yes, a constant loop is smaller and simpler, but unless the constant is also *small*, it sure isn't better.
Linus
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