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

[Linhaifeng <haifeng.lin@huawei.com>]

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
> to consider which is best strategy in terms of performance in future.
> How did you find this? through code review or real workload?

We found this through real workload which use vhost_net + virtio_pmd to forward packets in VM.

>> 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))) {
> 
> 
> 

-- 
Regards,
Haifeng