Re: [PATCH v3] io_uring: don't wait when under-submitting

Jens Axboe
2019-12-15T21:33:41Z

On 12/15/19 8:48 AM, Pavel Begunkov wrote:
> On 15/12/2019 08:42, Jens Axboe wrote:
>> On 12/14/19 11:43 AM, Jens Axboe wrote:
>>> On 12/14/19 7:53 AM, Pavel Begunkov wrote:
>>>> There is no reliable way to submit and wait in a single syscall, as
>>>> io_submit_sqes() may under-consume sqes (in case of an early error).
>>>> Then it will wait for not-yet-submitted requests, deadlocking the user
>>>> in most cases.
>>>>
>>>> In such cases adjust min_complete, so it won't wait for more than
>>>> what have been submitted in the current call to io_uring_enter(). It
>>>> may be less than totally in-flight including previous submissions,
>>>> but this shouldn't do harm and up to a user.
>>>
>>> Thanks, applied.
>>
>> This causes a behavioral change where if you ask to submit 1 but
>> there's nothing in the SQ ring, then you would get 0 before. Now
>> you get -EAGAIN. This doesn't make a lot of sense, since there's no
>> point in retrying as that won't change anything.
>>
>> Can we please just do something like the one I sent, instead of trying
>> to over-complicate it?
>>
>
> Ok, when I get to a compiler.

Great, thanks. BTW, I noticed when a regression test failed.

--
Jens Axboe