Re: [dpdk-dev] [PATCH] virtio: fix rx ring descriptor starvation

[Tom Kiely <tkiely@brocade.com>]

Hi,
    Sorry for the delay. I have been occupied on another critical issue. 
I'll look at this today.
    Tom

On 12/17/2015 04:47 AM, Xie, Huawei wrote:
> On 11/26/2015 1:33 AM, Xie, Huawei wrote:
>> On 11/13/2015 5:33 PM, Tom Kiely wrote:
>>> If all rx descriptors are processed while transient
>>> mbuf exhaustion is present, the rx ring ends up with
>>> no available descriptors. Thus no packets are received
>>> on that ring. Since descriptor refill is performed post
>>> rx descriptor processing, in this case no refill is
>>> ever subsequently performed resulting in permanent rx
>>> traffic drop.
>>>
>>> Signed-off-by: Tom Kiely <tkiely@brocade.com>
>>> ---
>>>   drivers/net/virtio/virtio_rxtx.c |    6 ++++--
>>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>>> index 5770fa2..a95e234 100644
>>> --- a/drivers/net/virtio/virtio_rxtx.c
>>> +++ b/drivers/net/virtio/virtio_rxtx.c
>>> @@ -586,7 +586,8 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
>>>   	if (likely(num > DESC_PER_CACHELINE))
>>>   		num = num - ((rxvq->vq_used_cons_idx + num) % DESC_PER_CACHELINE);
>>>   
>>> -	if (num == 0)
>>> +	/* Refill free descriptors even if no pkts recvd */
>>> +	if (num == 0 && virtqueue_full(rxvq))
>> Should the return condition be that no used buffers and we have avail
>> descs in avail ring, i.e,
>>      num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries
>>
>> rather than
>>      num == 0 && rxvq->vq_free_cnt == 0
>> ?
> Tom:
> Any further progress?
>>>   		return 0;
>>>   
>>>   	num = virtqueue_dequeue_burst_rx(rxvq, rcv_pkts, len, num);
>>> @@ -683,7 +684,8 @@ virtio_recv_mergeable_pkts(void *rx_queue,
>>>   
>>>   	virtio_rmb();
>>>   
>>> -	if (nb_used == 0)
>>> +	/* Refill free descriptors even if no pkts recvd */
>>> +	if (nb_used == 0 && virtqueue_full(rxvq))
>>>   		return 0;
>>>   
>>>   	PMD_RX_LOG(DEBUG, "used:%d\n", nb_used);