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

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

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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.

-- 
Pavel Begunkov


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