[dpdk-stable] [PATCH v1] net/virtio: fix vectorized Rx queue stuck

[David Christensen]

> When Rx queue worked in vectorized mode and rxd <= 512, under traffic of
> high PPS rate, testpmd often start and receive packets of rxd without
> further growth.
> 
> Testpmd started with rxq flush which tried to rx MAX_PKT_BURST(512)
> packets and drop. When Rx burst size >= Rx queue size, all descriptors
> in used queue consumed without rearm, device can't receive more packets.
> The next Rx burst returned at once since no used descriptors found,
> rearm logic was skipped, rx vq kept in starving state.
> 
> To avoid rx vq starving, this patch always check the available queue,
> rearm if needed even no used descriptor reported by device.
> 
> Fixes: fc3d66212fed ("virtio: add vector Rx")
> Cc: 谢华伟(此时此刻） <huawei.xhw at alibaba-inc.com>
> Fixes: 2d7c37194ee4 ("net/virtio: add NEON based Rx handler")
> Cc: jerin.jacob at caviumnetworks.com
> Fixes: 52b5a707e6ca ("net/virtio: add Altivec Rx")
> Cc: drc at linux.vnet.ibm.com
> Cc: stable at dpdk.org
> 
> Signed-off-by: Xueming Li <xuemingl at nvidia.com>
> ---
>   drivers/net/virtio/virtio_rxtx_simple_altivec.c | 12 ++++++------
>   drivers/net/virtio/virtio_rxtx_simple_neon.c    | 12 ++++++------
>   drivers/net/virtio/virtio_rxtx_simple_sse.c     | 12 ++++++------
>   3 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_rxtx_simple_altivec.c b/drivers/net/virtio/virtio_rxtx_simple_altivec.c
> index 62e5100a48..7534974ef4 100644
> --- a/drivers/net/virtio/virtio_rxtx_simple_altivec.c
> +++ b/drivers/net/virtio/virtio_rxtx_simple_altivec.c
> @@ -85,6 +85,12 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>   	if (unlikely(nb_pkts < RTE_VIRTIO_DESC_PER_LOOP))
>   		return 0;
> 
> +	if (vq->vq_free_cnt >= RTE_VIRTIO_VPMD_RX_REARM_THRESH) {
> +		virtio_rxq_rearm_vec(rxvq);
> +		if (unlikely(virtqueue_kick_prepare(vq)))
> +			virtqueue_notify(vq);
> +	}
> +
>   	nb_used = virtqueue_nused(vq);
> 
>   	rte_compiler_barrier();
> @@ -102,12 +108,6 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
> 
>   	rte_prefetch0(rused);
> 
> -	if (vq->vq_free_cnt >= RTE_VIRTIO_VPMD_RX_REARM_THRESH) {
> -		virtio_rxq_rearm_vec(rxvq);
> -		if (unlikely(virtqueue_kick_prepare(vq)))
> -			virtqueue_notify(vq);
> -	}
> -
>   	nb_total = nb_used;
>   	ref_rx_pkts = rx_pkts;
>   	for (nb_pkts_received = 0;

Reviewed-by: David Christensen <drc at linux.vnet.ibm.com>