Re: [LIBURING PATCH] sq_ring_needs_enter: check whether there are sqes when SQPOLL is not enabled

[Hrvoje Zeba <zeba.hrvoje@gmail.com>]

On Mon, Apr 13, 2020 at 11:29 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 4/13/20 1:19 AM, Xiaoguang Wang wrote:
> > Indeed I'm not sure this patch is necessary, robust applications
> > should not call io_uring_submit when there are not sqes to submmit.
> > But still try to add this check, I have seen some applications which
> > call io_uring_submit(), but there are not sqes to submit.
>
> Hmm, not sure it's worth complicating the submit path for that case.
> A high performant application should not call io_uring_submit() if
> it didn't queue anything new. Is this a common case you've seen?
>

My code calls io_uring_submit() even if there are no sqes to submit to
avoid spinning if there's nothing to do:

...
uint32_t sleep = (gt::user_contexts_waiting() > 0) ? 0 : 1;
auto res = io_uring_submit_and_wait(&m_io_uring, sleep);
...

-- 
I doubt, therefore I might be.