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

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/11/2014 15:06, Paolo Bonzini 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?

Ah, if !io_q.plugged we must be in the -EAGAIN case, so no need to 
"submit immediately if queue depth is above 2/3".  Can you rewrite the 
comment like this:

    /* This is reached in two cases: queue not plugged but io_submit
     * returned -EAGAIN, or queue plugged.  In the latter case, start
     * submitting some I/O if the queue is getting too full.  In the
     * former case, instead, wait until an I/O operation is completed.
     */
    if (likely(idx <= s->io_q.size * 2 / 3) || unlikely(!s->io_q.plugged) {
        return 0;
    }

Paolo