Re: [PATCH] io_uring: drain next sqe instead of shadowing

[Jens Axboe <axboe@kernel.dk>]

On 11/21/19 5:49 AM, Jackie Liu wrote:
> 
> 
> On 2019/11/21 20:40, Pavel Begunkov wrote:
>>> 在 2019/11/21 17:43, Pavel Begunkov 写道:
>>>> On 11/21/2019 12:26 PM, Jackie Liu wrote:
>>>>> 2019年11月21日 16:54，Pavel Begunkov <asml.silence@gmail.com> 写道：
>>>>>>
>>>>>> If there is a DRAIN in the middle of a link, it uses shadow req. Defer
>>>>>> the next request/link instead. This:
>>>>>>
>>>>>> Pros:
>>>>>> 1. removes semi-duplicated code
>>>>>> 2. doesn't allocate memory for shadows
>>>>>> 3. works better if only the head marked for drain
>>>>>
>>>>> I thought about this before, just only drain the head, but if the
>>>>> latter IO depends
>>>>> on the link-list, then latter IO will run in front of the link-list.
>>>>> If we think it
>>>>> is acceptable, then I think it is ok for me.
>>>>
>>>> If I got your point right, latter requests won't run ahead of the
>>>> link-list. There shouldn't be change of behaviour.
>>>>
>>>> The purpose of shadow requests is to mark some request right ahead of
>>>> the link for draining. This patch uses not a specially added shadow
>>>> request, but the following regular one. And, as drained IO shouldn't be
>>>> issued until every request behind completed, this should give the same
>>>> effect.
>>>>
>>>> Am I missed something?
>>>
>>> Thanks for explaining. This is also correct, if I understand
>>> correctly, It seems that other IOs will wait for all the links are
>>> done. this is a little different, is it?
>>
>> Yes, you're right, it also was briefly stated in the patch description
>> (see Cons). I hope, links + drain in the middle is an uncommon case.
>> But it can be added back, but may become a little bit uglier.
>>
>> What do you think, should we care about this case?
> 
> Yes, this is a very tiny scene. When I first time wrote this part of the
> code, my suggestion was to ban it directly.
> 
> For this patch, I am fine, Jens, what do you think.

I am fine with it as well, it'd be nice to get rid of needing that
extra request.

Was that a reviewed-by from you? It'd be nice to get these more
formally so I can add the attributes. I'll drop the other patch.

> The mailing list always rejects my mail, is my smtp server IP banned?

Probably because you have text/html in your email, the list is pretty
picky when it comes to anything that isn't just text/plain.

-- 
Jens Axboe