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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>,
	[email protected], [email protected]
Subject: Re: [PATCH v3] io_uring: don't wait when under-submitting
Date: Mon, 16 Dec 2019 19:47:23 +0300	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>


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On 16/12/2019 00:33, Jens Axboe wrote:
> 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.
> 

Yeah, I properly tested only the first one. Clearly, not as easy as
I thought, and there were more to consider.

I sent the next version, but that's odd basically taking your code.
Probably, it would have been easier for you to just commit it yourself.


-- 
Pavel Begunkov


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  parent reply	other threads:[~2019-12-16 16:47 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-13  7:51 [PATCH 1/1] io_uring: don't wait when under-submitting Pavel Begunkov
2019-12-13 18:22 ` Jens Axboe
2019-12-13 18:32   ` Jens Axboe
2019-12-13 21:32     ` Pavel Begunkov
2019-12-13 21:48       ` Jens Axboe
2019-12-14 14:31 ` [PATCH v2] " Pavel Begunkov
2019-12-14 14:39   ` Jens Axboe
2019-12-14 14:44     ` Pavel Begunkov
2019-12-14 14:53   ` [PATCH v3] " Pavel Begunkov
2019-12-14 18:43     ` Jens Axboe
2019-12-15  5:42       ` Jens Axboe
2019-12-15 15:48         ` Pavel Begunkov
2019-12-15 21:33           ` Jens Axboe
2019-12-16 16:31             ` [PATCH v4] " Pavel Begunkov
2019-12-16 16:47             ` Pavel Begunkov [this message]
2019-12-16 16:51               ` [PATCH v3] " Jens Axboe

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