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Date: Mon, 12 Oct 2015 16:39:56 +0800
From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Steffen Bauch <mail@steffenbauch.de>,
 Nikita Kalyazin <n.kalyazin@samsung.com>
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Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v5 resend 07/12] virtio: resolve for control
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On Thu, Oct 08, 2015 at 10:51:02PM +0200, Steffen Bauch wrote:
> 
> 
> On 10/08/2015 05:32 PM, Nikita Kalyazin wrote:
> >Hi Yuanhan,
> >
> >
> >As I understand, the dead loop happened here (virtio_send_command):
> >while (vq->vq_used_cons_idx == vq->vq_ring.used->idx) {
> >       rte_rmb();
> >       usleep(100);
> >}
> >
> >Could you explain why wrong config reading caused that and how correct reading helps to avoid?

Wrong config reading results to wrong config->max_virtqueue_pairs, which
ends up with wrong ctrl vq index being set:

    PMD: virtio_send_command(): vq->vq_queue_index = 37120

Note that you need enable CONFIG_RTE_LIBRTE_VIRTIO_DEBUG_INIT to see above
debug log.

That is to say we are waiting for the backend to consume a non-exist
queue, and that's how the dead loop comes.


> >
> Hi,
> 
> I just recognized that this dead loop is the same one that I have
> experienced (see
> http://dpdk.org/ml/archives/dev/2015-October/024737.html for
> reference). Just applying the changes in this patch (only 07/12)
> will not fix the dead loop at least in my setup.

Try to enable CONFIG_RTE_LIBRTE_VIRTIO_DEBUG_INIT, and dump more log?

	--yliu