Re: [dpdk-dev] [PATCH] lib/librte_pmd_virtio fix can't receive packets after rx_q is empty

["Xie, Huawei" <huawei.xie@intel.com>]

On 3/21/2015 10:25 AM, Linhaifeng wrote:
>
> On 2015/3/21 0:54, Xie, Huawei wrote:
>> On 3/20/2015 6:47 PM, linhaifeng wrote:
>>> From: Linhaifeng <haifeng.lin@huawei.com>
>>>
>>> If failed to alloc mbuf ring_size times the rx_q may be empty and can't
>>> receive any packets forever because nb_used is 0 forever.
>> Agreed. In current implementation, once VQ becomes empty, we have no
>> chance to refill it again.
>> The simple fix is, receive one and then refill one as other PMDs. Need
> "Receive one and then refill one" also have this problem.If refill also
> failed the VQ would be empty too.
Correction: refill one and receive one on success of refill
>
>> to consider which is best strategy in terms of performance in future.
>> How did you find this? through code review or real workload?
>>> so we should try to refill when nb_used is 0.After otherone free mbuf
>>> we can restart to receive packets.
>>>
>>> Signed-off-by: Linhaifeng <haifeng.lin@huawei.com>
>>> ---
>>>  lib/librte_pmd_virtio/virtio_rxtx.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/lib/librte_pmd_virtio/virtio_rxtx.c b/lib/librte_pmd_virtio/virtio_rxtx.c
>>> index 1d74b34..5c7e0cd 100644
>>> --- a/lib/librte_pmd_virtio/virtio_rxtx.c
>>> +++ b/lib/librte_pmd_virtio/virtio_rxtx.c
>>> @@ -495,7 +495,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
>>>  		num = num - ((rxvq->vq_used_cons_idx + num) % DESC_PER_CACHELINE);
>>>  
>>>  	if (num == 0)
>>> -		return 0;
>>> +		goto refill;
>>>  
>>>  	num = virtqueue_dequeue_burst_rx(rxvq, rcv_pkts, len, num);
>>>  	PMD_RX_LOG(DEBUG, "used:%d dequeue:%d", nb_used, num);
>>> @@ -536,6 +536,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
>>>  
>>>  	rxvq->packets += nb_rx;
>>>  
>>> +refill:
>>>  	/* Allocate new mbuf for the used descriptor */
>>>  	error = ENOSPC;
>>>  	while (likely(!virtqueue_full(rxvq))) {
>>
>>