Re: [PATCH 3/5] io_uring: implement our own schedule timeout handling

[David Wei <dw@davidwei.uk>]

On 2024-08-20 15:13, Pavel Begunkov wrote:
>>>>> On 8/20/24 2:08 PM, David Wei wrote:
>>>> To rephase the question, why is the original code calling
>>>> schedule_hrtimeout_range_clock() not needing to differentiate behaviour
>>>> between defer taskrun and not?
>>>
>>> Because that part is the same, the task schedules out and goes to sleep.
>>> That has always been the same regardless of how the ring is setup. Only
>>> difference is that DEFER_TASKRUN doesn't add itself to ctx->wait, and
>>> hence cannot be woken by a wake_up(ctx->wait). We have to wake the task
>>> manually.
>>>
>>
>> io_cqring_timer_wakeup() is the timer expired callback which calls
>> wake_up_process() or io_cqring_wake() depending on DEFER_TASKRUN.
>>
>> The original code calling schedule_hrtimeout_range_clock() uses
>> hrtimer_sleeper instead, which has a default timer expired callback set
>> to hrtimer_wakeup().
>>
>> hrtimer_wakeup() only calls wake_up_process().
>>
>> My question is: why this asymmetry? Why does the new custom callback
>> require io_cqring_wake()?
> 
> That's what I'm saying, it doesn't need and doesn't really want it.
> From the correctness point of view, it's ok since we wake up a
> (unnecessarily) larger set of tasks.
> 

Yeah your explanation that came in while I was writing the email
answered it, thanks Pavel.