Re: [linus:master] [iov_iter] c9eec08bac: vm-scalability.throughput -16.9% regression

Borislav Petkov
2023-11-15T19:10:08Z

On Wed, Nov 15, 2023 at 01:38:18PM -0500, Linus Torvalds wrote:
> It's probably completely broken. I particularly worry about "memcpy()"
> being used *during* the instruction rewriting, so the whole approach
> with ALTERNATIVE() is probably entirely broken.

Should we define an alternative_memcpy() which is used *only* during
rewriting so that this becomes a non-issue?

> But I'm cc'ing Borislav, because we've talked about the whole "inline
> memcpy() with alternatives" before, so maybe this gives Borislav some
> ideas for how to do it right.

Yours looks simple enough and makes sense. Lemme poke at it a bit in the
coming days and see what happens.

> Borislav, see
>
> https://lore.kernel.org/all/CAHk-=wjCUckvZUQf7gqp2ziJUWxVpikM_6srFdbcNdBJTxExRg@mail.gmail.com/
>
> for some truly crazy code generation by gcc.

Yeah, lemme show that to gcc folks. That asm is with your compiler,
right? Version?

Thx.

--
Regards/Gruss,
Boris.