On Tue, Jul 26, 2022 at 11:18 AM Yury Norov <yury.norov@xxxxxxxxx> 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
