Re: [PATCH 3/3] io_uring: add IORING_CQE_F_POLLED flag

[Jens Axboe <axboe@kernel.dk>]

On 7/12/25 3:02 PM, Jens Axboe wrote:
> On 7/12/25 8:49 AM, Pavel Begunkov wrote:
>> On 7/12/25 12:34, Pavel Begunkov wrote:
>>> On 7/12/25 00:59, Jens Axboe wrote:
>>> ...>       /*
>>>>        * If multishot has already posted deferred completions, ensure that
>>>>        * those are flushed first before posting this one. If not, CQEs
>>>> diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
>>>> index dc17162e7af1..d837e02d26b2 100644
>>>> --- a/io_uring/io_uring.h
>>>> +++ b/io_uring/io_uring.h
>>>> @@ -235,6 +235,8 @@ static inline void req_set_fail(struct io_kiocb *req)
>>>>   static inline void io_req_set_res(struct io_kiocb *req, s32 res, u32 cflags)
>>>>   {
>>>> +    if (req->flags & REQ_F_POLL_WAKE)
>>>> +        cflags |= IORING_CQE_F_POLLED;
>>>
>>> Can you avoid introducing this new uapi (and overhead) for requests that
>>> don't care about it please? It's useless for multishots, and the only
>>> real potential use case is send requests.
>>
>> Another thought, I think the userspace can already easily infer
>> information similar to what this flag gives. E.g. peek at CQEs
>> right after submission and mark the inverse of the flag. The
>> actual impl can be made nicer than that.
> 
> As per the previous reply, not sure it makes a ton of sense. The initial
> hack I did was just for sends, and it actually just reused the bit for
> SOCK_NONEMPTY, as it was only for writes. But then the concept seemed
> generic enough that it'd be useful for writes. And then it becomes
> mostly a "did I poll thing", which obviously then makes sense for single
> shot read/recv as well.
> 
> Now it's taking a new bit, which isn't great.
> 
> But I think it's one of those things that need to ruminate a bit. Maybe
> just go back to doing it purely for sends. But then perhaps you'd
> actually want to know if the NEXT send would block, not that your
> current one did.

This is closer to what I originally had:

https://git.kernel.dk/cgit/linux/log/?h=io_uring-send-full

with adding REQ_F_POLL_ARMED and then using that just on the send
side. And reusing the value of SOCK_NONEMPTY, as that one is just
for receives, and this one is just for sends.

-- 
Jens Axboe