[Twisted-Python] reactor for Linux io_uring

[Tobias Oberstein]

interesting. thanks!

Am 12.03.21 um 09:59 schrieb Ian Haywood:
> On 12/03/2021 7:21 pm, Tobias Oberstein wrote:
>> sorry, I missed the beginning of the thread / discussion: are you 
>> working on a new, full Twisted reactor on top of io_uring?
>>
>> and async filesystem is "just" one part / additional effort in that? 
> the advantage of io_uring is being able to combine file and network I/O, 
> so this PR is a precondition to working on the reactor.

yeah, the advantages of io_uring are obvious, combining disk and network 
IO is one. even a network IO only twisted reactor for io_uring would be 
awesome! disk IO, for me, would be nice to have, but depends, eg LMDB 
mmaps the DB file, so it wouldn't go through io_uring anyways.

one more aspect: io_uring is also about zero-copy (besides reducing 
context switch overhead / reduce syscalls)

twisted protocol base classes always first buffer outgoing bytes in 
userspace. in a list that is later flattened, before pushing to kernel 
in the actual socket write. the latter only happens once the FD being 
written becomes writable of course.

since with io_uring the queue/ring to append to never blocks for writes, 
that buffering in twisted would lead to double buffering (as the ring 
already buffers)

then, io_uring follows a completion IO model (as IOCP). quite different 
from the "ready to write/read" model (as in epoll etc).

I am wondering, do you already have a design for these aspects of 
io_uring / twisted?

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