[dpdk-dev] [PATCH v2 5/5] lib_vhost: Add support copying scattered mbuf to vring

[Xie, Huawei]

virtio_dev_rx & scatter_rx & merge-able rx should be merged and the code
could be much simpler, unless there is special performance consideration.


On 5/28/2015 11:17 PM, Ouyang, Changchun wrote:
> Add support copying scattered mbuf to vring which is done by dev_scatter_rx,
> and check the 'next' pointer in mbuf on the fly to select suitable function to rx packets.
>
> Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
> ---
>  lib/librte_vhost/vhost_rxtx.c | 116 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 115 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> index bb56ae1..3086bb4 100644
> --- a/lib/librte_vhost/vhost_rxtx.c
> +++ b/lib/librte_vhost/vhost_rxtx.c
> @@ -46,7 +46,8 @@
>   * This function adds buffers to the virtio devices RX virtqueue. Buffers can
>   * be received from the physical port or from another virtio device. A packet
>   * count is returned to indicate the number of packets that are succesfully
> - * added to the RX queue. This function works when mergeable is disabled.
> + * added to the RX queue. This function works when mergeable is disabled and
> + * the mbuf is not scattered.
>   */
>  static inline uint32_t __attribute__((always_inline))
>  virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
> @@ -447,6 +448,103 @@ fill_buf_vec(struct vhost_virtqueue *vq, uint16_t id, uint32_t *vec_idx)
>  }
>  
>  /*
> + * This function works for scatter-gather RX.
> + */
> +static inline uint32_t __attribute__((always_inline))
> +virtio_dev_scatter_rx(struct virtio_net *dev, uint16_t queue_id,
> +	struct rte_mbuf **pkts, uint32_t count)
> +{
> +	struct vhost_virtqueue *vq;
> +	uint32_t pkt_idx = 0, entry_success = 0;
> +	uint16_t avail_idx;
> +	uint16_t res_base_idx, res_end_idx;
> +	uint8_t success = 0;
> +
> +	LOG_DEBUG(VHOST_DATA, "(%"PRIu64") virtio_dev_scatter_rx()\n",
> +		dev->device_fh);
use __func__
> +	if (unlikely(queue_id != VIRTIO_RXQ))
> +		LOG_DEBUG(VHOST_DATA, "mq isn't supported in this version.\n");
> +
> +	vq = dev->virtqueue[VIRTIO_RXQ];
> +	count = RTE_MIN((uint32_t)MAX_PKT_BURST, count);
> +
> +	if (count == 0)
> +		return 0;
> +
> +	for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
> +		uint32_t secure_len = 0;
> +		uint32_t vec_idx = 0;
> +		uint32_t pkt_len = pkts[pkt_idx]->pkt_len + vq->vhost_hlen;
> +
> +		do {
> +			/*
> +			 * As many data cores may want access to available
> +			 * buffers, they need to be reserved.
> +			 */
> +			res_base_idx = vq->last_used_idx_res;
> +			avail_idx = *((volatile uint16_t *)&vq->avail->idx);
> +
> +			if (unlikely(res_base_idx == avail_idx)) {
> +				LOG_DEBUG(VHOST_DATA,
> +					"(%"PRIu64") Failed "
> +					"to get enough desc from "
> +					"vring\n",
> +					dev->device_fh);
> +				return pkt_idx;
> +			} else {
> +				uint16_t wrapped_idx =
> +					(res_base_idx) & (vq->size - 1);
> +				uint32_t idx = vq->avail->ring[wrapped_idx];
> +
> +				update_secure_len(vq, idx, &secure_len);
> +			}
> +
> +			if (pkt_len > secure_len) {
> +				LOG_DEBUG(VHOST_DATA,
> +					"(%"PRIu64") Failed "
> +					"to get enough desc from "
> +					"vring\n",
> +					dev->device_fh);
> +				return pkt_idx;
> +			}
The behavior for virtio_dev_rx and virtio_dev_merge_rx is totally
different. I think they should behave in the same way.
virtio_dev_rx updates used->len to zero while this one returns immediately.

Besides, with this implementation, if the caller retransmit the
mbuf(which has pkt_len larger the secure_len), it will enter endless loop.

> +
> +			/* vq->last_used_idx_res is atomically updated. */
> +			success = rte_atomic16_cmpset(&vq->last_used_idx_res,
> +							res_base_idx,
> +							res_base_idx + 1);
> +		} while (success == 0);

Here the behavior becomes different again in reserving vring entries.

> +
> +		fill_buf_vec(vq, res_base_idx, &vec_idx);
> +
> +		res_end_idx = res_base_idx + 1;
> +
> +		entry_success = copy_from_mbuf_to_vring(dev, res_base_idx,
> +			res_end_idx, pkts[pkt_idx]);
> +
> +		rte_compiler_barrier();
> +
> +		/*
> +		 * Wait until it's our turn to add our buffer
> +		 * to the used ring.
> +		 */
> +		while (unlikely(vq->last_used_idx != res_base_idx))
> +			rte_pause();
> +
> +		*(volatile uint16_t *)&vq->used->idx += entry_success;
> +		vq->last_used_idx = res_end_idx;
> +
> +		/* flush used->idx update before we read avail->flags. */
> +		rte_mb();
> +
> +		/* Kick the guest if necessary. */
> +		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
> +			eventfd_write((int)vq->callfd, 1);
> +	}
> +
> +	return count;
> +}
> +
> +/*
>   * This function works for mergeable RX.
>   */
>  static inline uint32_t __attribute__((always_inline))
> @@ -545,12 +643,28 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
>  	return count;
>  }
>  
> +/*
> + * Return 1 if any mbuf is scattered, otherwise return 0.
> + */
> +static inline uint32_t __attribute__((always_inline))
> +check_scatter(struct rte_mbuf **pkts, uint16_t count)
> +{
> +	uint32_t i;
> +	for (i = 0; i < count; i++) {
> +		if (pkts[i]->next != NULL)
> +			return 1;
> +	}
> +	return 0;
> +}
> +
>  uint16_t
>  rte_vhost_enqueue_burst(struct virtio_net *dev, uint16_t queue_id,
>  	struct rte_mbuf **pkts, uint16_t count)
>  {
>  	if (unlikely(dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF)))
>  		return virtio_dev_merge_rx(dev, queue_id, pkts, count);
> +	else if (unlikely(check_scatter(pkts, count) == 1))
> +		return virtio_dev_scatter_rx(dev, queue_id, pkts, count);
>  	else
>  		return virtio_dev_rx(dev, queue_id, pkts, count);
>  }