Re: [PATCH 3/8] io_uring: add a limited tw list for irq completion work

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

On 9/28/21 5:55 PM, Hao Xu wrote:
> 在 2021/9/28 下午7:29, Pavel Begunkov 写道:
[...]
>> It solves the problem of total starvation of non-prio requests, e.g.
>> if new completions coming as fast as you complete previous ones. One
>> downside is that prio requests coming while we execute a previous
>> batch will be executed only after a previous batch of non-prio
>> requests, I don't think it's much of a problem but interesting to
>> see numbers.
> Actually this was one of my implementation, I splited it to two lists
> explicitly most because the convience of 8/8 batch the tw in prior list.
> I'll evaluate the overhead tomorrow.

I guess so because it more resembles v1 but without inverting order
of the IRQ sublist.


>>
>>>           INIT_WQ_LIST(&tctx->task_list);
>>> +        INIT_WQ_LIST(&tctx->prior_task_list);
>>> +        tctx->nr = tctx->prior_nr = 0;
>>>           if (!node)
>>>               tctx->task_running = false;
>>>           spin_unlock_irq(&tctx->task_lock);
>>> @@ -2166,7 +2174,7 @@ static void tctx_task_work(struct callback_head *cb)
>>>       ctx_flush_and_put(ctx, &locked);
>>>   }
>>>   -static void io_req_task_work_add(struct io_kiocb *req)
>>> +static void io_req_task_work_add(struct io_kiocb *req, bool emergency)
>>
>> It think "priority" instead of "emergency" will be more accurate
>>
>>>   {
>>>       struct task_struct *tsk = req->task;
>>>       struct io_uring_task *tctx = tsk->io_uring;
>>> @@ -2178,7 +2186,13 @@ static void io_req_task_work_add(struct io_kiocb *req)
>>>       WARN_ON_ONCE(!tctx);
>>>         spin_lock_irqsave(&tctx->task_lock, flags);
>>> -    wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
>>> +    if (emergency && tctx->prior_nr * MAX_EMERGENCY_TW_RATIO < tctx->nr) {
>>> +        wq_list_add_tail(&req->io_task_work.node, &tctx->prior_task_list);
>>> +        tctx->prior_nr++;
>>> +    } else {
>>> +        wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
>>> +    }
>>> +    tctx->nr++;
>>>       running = tctx->task_running;
>>>       if (!running)
>>>           tctx->task_running = true;

-- 
Pavel Begunkov