Re: Linux 5.19-rc8

Linus Torvalds
2022-07-26T18:36:48Z

On Tue, Jul 26, 2022 at 11:18 AM Yury Norov <yury.norov@gmail.com> wrote:
>
> We have find_bit_benchmark to check how it works in practice. Would
> be great if someone with access to the hardware can share numbers.

Honestly, I doubt benchmarking find_bit in a loop is all that sensible.

These are helper functions that are probably seldom super-hot in
cache, and as with so many of these things, I suspect the cool-I$
numbers are the ones that matter most in real life.

When some filesystem ends up searching for a free block or similar, it
will probably have done other things before that that means that the
L1 I$ has been long flushed, and branch history is quite possibly
entirely gone too.

The same is quite possibly true for the bitmap itself in D$ too.

That said, looking at the x86 code generation (not only because I have
the build environment, but where I can actually read make sense of the
asm), the only thing that looks bad is the conditional bswap.

So the code gen looks fairly good,

Linus