Re: [LSF/MM/BPF ATTEND][LSF/MM/BPF Topic] Non-block IO

[Kanchan Joshi <joshiiitr@gmail.com>]

> > 4. Direct NVMe queues - will there be interest in having io_uring
> > managed NVMe queues?  Sort of a new ring, for which I/O is destaged from
> > io_uring SQE to NVMe SQE without having to go through intermediate
> > constructs (i.e., bio/request). Hopefully,that can further amp up the
> > efficiency of IO.
>
> This is interesting, and I've pondered something like that before too. I
> think it's worth investigating and hacking up a prototype. I recently
> had one user of IOPOLL assume that setting up a ring with IOPOLL would
> automatically create a polled queue on the driver side and that is what
> would be used for IO. And while that's not how it currently works, it
> definitely does make sense and we could make some things faster like
> that. It would also potentially easier enable cancelation referenced in
> #1 above, if it's restricted to the queue(s) that the ring "owns".

So I am looking at prototyping it, exclusively for the polled-io case.
And for that, is there already a way to ensure that there are no
concurrent submissions to this ring (set with IORING_SETUP_IOPOLL
flag)?
That will be the case generally (and submissions happen under
uring_lock mutex), but submission may still get punted to io-wq
worker(s) which do not take that mutex.
So the original task and worker may get into doing concurrent submissions.

The flag IORING_SETUP_SINGLE_ISSUER - is not for this case, or is it?