Re: [PATCH 4/6] io_uring: let fast poll support multishot

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

On 9/6/21 6:40 PM, Hao Xu wrote:
> 在 2021/9/6 下午11:56, Pavel Begunkov 写道:
>> On 9/3/21 12:00 PM, Hao Xu wrote:
>>> For operations like accept, multishot is a useful feature, since we can
>>> reduce a number of accept sqe. Let's integrate it to fast poll, it may
>>> be good for other operations in the future.
>>
>> __io_arm_poll_handler()         |
>>    -> vfs_poll()                 |
>>                                  | io_async_task_func() // post CQE
>>                                  | ...
>>                                  | do_apoll_rewait();
>>    -> continues after vfs_poll(),|
>>       removing poll->head of     |
>>       the second poll attempt.   |
>>
>>
> Sorry.. a little bit confused by this case, would you mind explain a bit
> more..is the right part a system-workqueue context? and is
> do_apoll_rewait() io_poll_rewait() function?

I meant in a broad sense. If your patches make lifetime of an accept
request to be like:

accept() -> arm_apoll() -> apoll_func() -> accept() -> ...
    -> ... (repeat many times)

then do_apoll_rewait() is the second accept in the scheme.

If not, and it's

accept() -> arm_poll() -> apoll_func() -> apoll_func() ->
 ... -> ?

Then that "do_apoll_rewait()" should have been second and
other apoll_func()s.

So, it's rather a thing to look after, but not a particular
bug.


>> One of the reasons for forbidding multiple apoll's is that it
>> might be racy. I haven't looked into this implementation, but
>> we should check if there will be problems from that.
>>
>> FWIW, putting aside this patchset, the poll/apoll is not in
>> the best shape and can use some refactoring.
>>
>>
[...]

-- 
Pavel Begunkov