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Date: Mon, 24 Nov 2014 12:38:56 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v4 2/3] linux-aio: handling -EAGAIN for
 !s->io_q.plugged case
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To: Ming Lei <ming.lei@canonical.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Kevin Wolf <kwolf@redhat.com>



On 24/11/2014 12:31, Ming Lei wrote:
> +    /* don't submit until next completion for -EAGAIN of non plug case */
> +    if (unlikely(!s->io_q.plugged)) {
> +        return 0;
> +    }
> +
>      /* submit immediately if queue depth is above 2/3 */
>      if (idx > s->io_q.size * 2 / 3) {
>          return ioq_submit(s);
      }

      return 0;

so I fail to see why my proposal:


    /* 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;
    }

    return ioq_submit(s);

was wrong.  Can you explain?

Paolo