Re: [GIT PULL] io_uring support for zerocopy send

Linus Torvalds
2022-08-02T20:45:55Z

On Sun, Jul 31, 2022 at 8:03 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> On top of the core io_uring changes, this pull request adds support for
> efficient support for zerocopy sends through io_uring. Both ipv4 and
> ipv6 is supported, as well as both TCP and UDP.

I've pulled this, but I would *really* have wanted to see real
performance numbers from real loads.

Zero-copy networking has decades of history (and very much not just in
Linux) of absolutely _wonderful_ benchmark numbers, but less-than
impressive take-up on real loads.

A lot of the wonderful benchmark numbers are based on loads that
carefully don't touch the data on either the sender or receiver side,
and that get perfect behavior from a performance standpoint as a
result, but don't actually do anything remotely realistic in the
process.

Having data that never resides in the CPU caches, or having mappings
that are never written to and thus never take page faults are classic
examples of "look, benchmark numbers!".

Please?

Linus