Re: Large CQE for fuse headers

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/10/24 21:56, Bernd Schubert wrote:
> Hello,
> 
> as discussed during LPC, we would like to have large CQE sizes, at least
> 256B. Ideally 256B for fuse, but CQE512 might be a bit too much...
> 
> Pavel said that this should be ok, but it would be better to have the CQE
> size as function argument.
> Could you give me some hints how this should look like and especially how

I remembered it as SQEs, which would've been much easier. In the current
io_uring infra, usually to post a cqe an opcode specific path stashed the
result value in the request structure and then the core io_uring code will
post it for you. We won't find space for 256B, however, and it'd need to
happen right from the cmd path and follow the rules when / from what
context it can be posted.

I'll take a stub to see how it can look like.

> we are going to communicate the CQE size to the kernel? I guess just adding
> IORING_SETUP_CQE256 / IORING_SETUP_CQE512 would be much easier.

3-4 special cases is already odd as an API, we should rather just
pass the desired CQE size.

> I'm basically through with other changes Miklos had been asking for and
> moving fuse headers into the CQE is next.

-- 
Pavel Begunkov