Re: [Qemu-devel] [PATCH v3 2/3] linux-aio: handling -EAGAIN for !s->io_q.plugged case

[Ming Lei]

On Tue, Nov 18, 2014 at 10:06 PM, Paolo Bonzini <address@hidden> wrote:
>
>
> On 06/11/2014 16:10, Ming Lei wrote:
>> +    /* don't submit until next completion for -EAGAIN of non plug case */
>> +    if (unlikely(!s->io_q.plugged)) {
>> +        return 0;
>> +    }
>> +
>
> Is this an optimization or a fix for something?

It is for avoiding unnecessary submission which will cause
another -EAGAIN.

>
>> +        /*
>> +         * Switch to queue mode until -EAGAIN is handled, we suppose
>> +         * there is always uncompleted I/O, so try to enqueue it first,
>> +         * and will be submitted again in following aio completion cb.
>> +         */
>> +        if (ret == -EAGAIN) {
>> +            goto enqueue;
>> +        } else if (ret < 0) {
>>              goto out_free_aiocb;
>>          }
>
> Better:
>
>      if (!s->io_q.plugged && !s->io_q.idx) {
>         ret = io_submit(s->ctx, 1, &iocbs);
>         if (ret >= 0) {
>             return &laiocb->common;
>         }
>         if (ret != -EAGAIN) {
>             goto out_free_aiocb;
>         }
>     }

Right.

Thanks,
Ming Lei