Re: [PATCH 2/2] io_uring: implement async hybrid mode for pollable requests

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/10/18 下午8:10, Pavel Begunkov 写道:
> On 10/18/21 11:34, Hao Xu wrote:
>> 在 2021/10/18 下午7:29, Hao Xu 写道:
>>> The current logic of requests with IOSQE_ASYNC is first queueing it to
>>> io-worker, then execute it in a synchronous way. For unbound works like
>>> pollable requests(e.g. read/write a socketfd), the io-worker may stuck
>>> there waiting for events for a long time. And thus other works wait in
>>> the list for a long time too.
>>> Let's introduce a new way for unbound works (currently pollable
>>> requests), with this a request will first be queued to io-worker, then
>>> executed in a nonblock try rather than a synchronous way. Failure of
>>> that leads it to arm poll stuff and then the worker can begin to handle
>>> other works.
>>> The detail process of this kind of requests is:
>>>
>>> step1: original context:
>>>             queue it to io-worker
>>> step2: io-worker context:
>>>             nonblock try(the old logic is a synchronous try here)
>>>                 |
>>>                 |--fail--> arm poll
>>>                              |
>>>                              |--(fail/ready)-->synchronous issue
>>>                              |
>>>                              |--(succeed)-->worker finish it's job, tw
>>>                                             take over the req
>>>
>>> This works much better than the old IOSQE_ASYNC logic in cases where
>>> unbound max_worker is relatively small. In this case, number of
>>> io-worker eazily increments to max_worker, new worker cannot be created
>>> and running workers stuck there handling old works in IOSQE_ASYNC mode.
>>>
>>> In my 64-core machine, set unbound max_worker to 20, run echo-server,
>>> turns out:
>>> (arguments: register_file, connetion number is 1000, message size is 12
>>> Byte)
>>> original IOSQE_ASYNC: 76664.151 tps
>>> after this patch: 166934.985 tps
>>>
>>> Suggested-by: Jens Axboe <axboe@kernel.dk>
>>> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
>> An irrelevant question: why do we do linked timeout logic in
>> io_wq_submit_work() again regarding that we've already done it in
>> io_queue_async_work().
> 
> Because io_wq_free_work() may enqueue new work (by returning it)
> without going through io_queue_async_work(), and we don't care
> enough to split those cases.
Make sense. Thanks.
>