Re: [dpdk-dev] [PATCH v7 5/8] net/virtio: implement transmit path for packed queues

[Jens Freimann <jfreimann@redhat.com>]

On Thu, Oct 11, 2018 at 07:31:57PM +0200, Maxime Coquelin wrote:
>
>I'm testing your series, and it gets stuck after 256 packets in transmit
>path. When it happens, descs flags indicate it has been made available
>by the driver (desc->flags = 0x80), but it is not consistent with the
>expected wrap counter value (0).
>
>Not sure this is the root cause, but it seems below code is broken:

>
>On 10/03/2018 03:11 PM, Jens Freimann wrote:

[snip]
>+
>>+	do {
>>+		if (idx >= vq->vq_nentries) {
>>+			idx = 0;
>>+			vq->vq_ring.avail_wrap_counter ^= 1;
>>+		}
>>+		start_dp[idx].addr  = VIRTIO_MBUF_DATA_DMA_ADDR(cookie, vq);
>>+		start_dp[idx].len   = cookie->data_len;
>>+		start_dp[idx].flags = cookie->next ? VRING_DESC_F_NEXT : 0;
>>+		start_dp[idx].flags |=
>>+			VRING_DESC_F_AVAIL(vq->vq_ring.avail_wrap_counter) |
>>+			VRING_DESC_F_USED(!vq->vq_ring.avail_wrap_counter);
>>+		if (use_indirect) {
>>+			if (++idx >= (seg_num + 1))
>>+				break;
>>+		} else {
>>+			dxp = &vq->vq_descx[idx];
>>+			idx = dxp->next;
>>+		}
>
>Imagine current idx is 255, dxp->next will give idx 0, right?

No it will be VQ_RING_DESC_CHAIN_END which is defined as 32768. 

>In that case, for desc[0], on next iteration, the flags won't be set 
>available properly, as vq->vq_ring.avail_wrap_counter isn't updated.

It will wrap because VQ_RING_DESC_CHAIN_END is > ring size.

I can't reproduce what you see. Do you test with txonly fwd mode?

regards,
Jens