On Wed, May 04, 2022 at 01:40:07PM -0700, Linus Torvalds wrote:
> Sadly, I'm on Zen2 with my 3970X, and the Zen 3 threadrippers seem to
> be basically impossible to get.
Yeah, what we did is get a gigabyte board:
[ 0.000000] DMI: GIGABYTE MZ32-AR0-00/MZ32-AR0-00, BIOS M06 07/10/2021
and stick a server CPU in it:
[ 2.352371] smpboot: CPU0: AMD EPYC 7313 16-Core Processor (family: 0x19, model: 0x1, stepping: 0x1)
so that we can have the memory encryption stuff. 32 threads is fairly
decent and kernel builds are fast enough, at least for me. If you need
to do a lot of allmodconfigs, you probably need something bigger though.
> Oh, the clear_user() in the ELF loader? I wouldn't have expected that
> to be noticeable.
Yah, that guy in load_elf_binary(). At least it did hit my breakpoint
fairly often so I thought, what is a benchmark that does create a lot of
processes...
> Now, clear_page() is *very* noticeable, but that has its own special
> magic and doesn't use clear_user().
Yeah, that's with the alternative CALL thing. Could be useful to try to
see how much the inlined rep; movsb would bring...
> Maybe there is some other clear_user() case I never thought of. My
> dim memories of profiles definitely had copy_to_user, clear_page and
> copy_page being some of the top copy loops.
I could try to do a perf probe or whatever fancy new thing we do now on
clear_user to get some numbers of how many times it gets called during
the benchmark run. Or do you wanna know the callers too?
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
