Re: Reimplementing ASIOs

From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2024-07-18 21:53:41

On 18/07/2024 22:34, Virgilio Fornazin via Boost wrote:
> a good point is to support sendmmsg / recvmmsg on linux/bsd (macos similar
> syscall SYS_sendmsg_x / SYS_recvmsg_x)
> to get good UDP throughput support.
> 
> I didn't find io_uring support for sendmmsg/recvmmsg at that time, maybe a
> time you could get coding / pushing this too.

I believe the mm-variants of send and receive take a very different code 
path to what io_uring uses, so it will never support those.

It's a bit like the other zero copy i/o path in Linux, it uses a weird 
code path to work and io_uring won't support it, ever. So they're 
forging ahead with their own zero copy approach which I believe requires 
NIC driver support, otherwise you get silent memory copying.

I haven't personally tested it, but the multishot receive feature of 
io_uring should get quite close to recvmmsg performance.

In any case, the once class leading UDP performance in Windows RIO Linux 
is steadily closing the gap. I believe FreeBSD still holds the record 
for the most packets switched per core per second, and that probably 
matters more for real world performance.

Niall