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().