> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> Sent: Saturday, September 5, 2015 4:58 AM
> To: Xie, Huawei; Ouyang, Changchun
> Cc: dev at dpdk.org; Stephen Hemminger
> Subject: [PATCH 3/4] virtio: use indirect ring elements
>
> The virtio ring in QEMU/KVM is usually limited to 256 entries and the normal
> way that virtio driver was queuing mbufs required nsegs + 1 ring elements.
> By using the indirect ring element feature if available, each packet will take
> only one ring slot even for multi-segment packets.
>
> Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
> ---
> drivers/net/virtio/virtio_ethdev.c | 11 +++++---
> drivers/net/virtio/virtio_ethdev.h | 3 ++-
> drivers/net/virtio/virtio_rxtx.c | 51 ++++++++++++++++++++++++++++++-
> -------
> drivers/net/virtio/virtqueue.h | 8 ++++++
> 4 files changed, 57 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index 465d3cd..bcfb87b 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -359,12 +359,15 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
> if (queue_type == VTNET_TQ) {
> /*
> * For each xmit packet, allocate a virtio_net_hdr
> + * and indirect ring elements
> */
> snprintf(vq_name, sizeof(vq_name),
> "port%d_tvq%d_hdrzone",
> - dev->data->port_id, queue_idx);
> - vq->virtio_net_hdr_mz =
> rte_memzone_reserve_aligned(vq_name,
> - vq_size * hw->vtnet_hdr_size,
> - socket_id, 0, RTE_CACHE_LINE_SIZE);
> + dev->data->port_id, queue_idx);
> +
> + vq->virtio_net_hdr_mz =
> + rte_memzone_reserve_aligned(vq_name,
> + vq_size * sizeof(struct
> virtio_tx_region),
> + socket_id, 0,
> RTE_CACHE_LINE_SIZE);
> if (vq->virtio_net_hdr_mz == NULL) {
> if (rte_errno == EEXIST)
> vq->virtio_net_hdr_mz =
> diff --git a/drivers/net/virtio/virtio_ethdev.h
> b/drivers/net/virtio/virtio_ethdev.h
> index 9026d42..07a9265 100644
> --- a/drivers/net/virtio/virtio_ethdev.h
> +++ b/drivers/net/virtio/virtio_ethdev.h
> @@ -64,7 +64,8 @@
> 1u << VIRTIO_NET_F_CTRL_VQ | \
> 1u << VIRTIO_NET_F_CTRL_RX | \
> 1u << VIRTIO_NET_F_CTRL_VLAN | \
> - 1u << VIRTIO_NET_F_MRG_RXBUF)
> + 1u << VIRTIO_NET_F_MRG_RXBUF | \
> + 1u << VIRTIO_RING_F_INDIRECT_DESC)
>
> /*
> * CQ function prototype
> diff --git a/drivers/net/virtio/virtio_rxtx.c
> b/drivers/net/virtio/virtio_rxtx.c
> index dbe6665..8979695 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -199,14 +199,15 @@ virtqueue_enqueue_recv_refill(struct virtqueue
> *vq, struct rte_mbuf *cookie) }
>
> static int
> -virtqueue_enqueue_xmit(struct virtqueue *txvq, struct rte_mbuf *cookie)
> +virtqueue_enqueue_xmit(struct virtqueue *txvq, struct rte_mbuf *cookie,
> + int use_indirect)
> {
> struct vq_desc_extra *dxp;
> struct vring_desc *start_dp;
> uint16_t seg_num = cookie->nb_segs;
> - uint16_t needed = 1 + seg_num;
> + uint16_t needed = use_indirect ? 1 : 1 + seg_num;
> uint16_t head_idx, idx;
> - uint16_t head_size = txvq->hw->vtnet_hdr_size;
> + unsigned long offs;
>
> if (unlikely(txvq->vq_free_cnt == 0))
> return -ENOSPC;
> @@ -220,11 +221,26 @@ virtqueue_enqueue_xmit(struct virtqueue *txvq,
> struct rte_mbuf *cookie)
> dxp = &txvq->vq_descx[idx];
> dxp->cookie = (void *)cookie;
> dxp->ndescs = needed;
> -
> start_dp = txvq->vq_ring.desc;
> - start_dp[idx].addr =
> - txvq->virtio_net_hdr_mem + idx * head_size;
> - start_dp[idx].len = (uint32_t)head_size;
> +
> + if (use_indirect) {
> + offs = offsetof(struct virtio_tx_region, tx_indir)
> + + idx * sizeof(struct virtio_tx_region);
> +
> + start_dp[idx].addr = txvq->virtio_net_hdr_mem + offs;
> + start_dp[idx].len = sizeof(struct vring_desc);
Should the length be N * sizeof(struct vring_desc)?
> + start_dp[idx].flags = VRING_DESC_F_INDIRECT;
> +
> + start_dp = (struct vring_desc *)
> + ((char *)txvq->virtio_net_hdr_mz->addr + offs);
> + idx = 0;
> + }
> +
> + offs = offsetof(struct virtio_tx_region, tx_hdr)
> + + idx * sizeof(struct virtio_tx_region);
> +
> + start_dp[idx].addr = txvq->virtio_net_hdr_mem + offs;
> + start_dp[idx].len = txvq->hw->vtnet_hdr_size;
> start_dp[idx].flags = VRING_DESC_F_NEXT;
>
> for (; ((seg_num > 0) && (cookie != NULL)); seg_num--) { @@ -236,7
> +252,12 @@ virtqueue_enqueue_xmit(struct virtqueue *txvq, struct
> rte_mbuf *cookie)
> }
>
> start_dp[idx].flags &= ~VRING_DESC_F_NEXT;
> - idx = start_dp[idx].next;
> +
> + if (use_indirect)
> + idx = txvq->vq_ring.desc[head_idx].next;
> + else
> + idx = start_dp[idx].next;
> +
> txvq->vq_desc_head_idx = idx;
> if (txvq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
> txvq->vq_desc_tail_idx = idx;
> @@ -760,7 +781,15 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
>
> for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
> struct rte_mbuf *txm = tx_pkts[nb_tx];
> - int need = txm->nb_segs - txvq->vq_free_cnt + 1;
> + int use_indirect, slots, need;
> +
> + use_indirect = vtpci_with_feature(txvq->hw,
> +
> VIRTIO_RING_F_INDIRECT_DESC)
> + && (txm->nb_segs < VIRTIO_MAX_TX_INDIRECT);
> +
> + /* How many ring entries are needed to this Tx? */
> + slots = use_indirect ? 1 : 1 + txm->nb_segs;
> + need = slots - txvq->vq_free_cnt;
>
> /* Positive value indicates it need free vring descriptors */
> if (need > 0) {
> @@ -769,7 +798,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
> need = RTE_MIN(need, (int)nb_used);
>
> virtio_xmit_cleanup(txvq, need);
> - need = txm->nb_segs - txvq->vq_free_cnt + 1;
> + need = slots - txvq->vq_free_cnt;
> if (unlikely(need > 0)) {
> PMD_TX_LOG(ERR,
> "No free tx descriptors to
> transmit");
> @@ -787,7 +816,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
> }
>
> /* Enqueue Packet buffers */
> - error = virtqueue_enqueue_xmit(txvq, txm);
> + error = virtqueue_enqueue_xmit(txvq, txm, use_indirect);
> if (unlikely(error)) {
> if (error == ENOSPC)
> PMD_TX_LOG(ERR, "virtqueue_enqueue
> Free count = 0"); diff --git a/drivers/net/virtio/virtqueue.h
> b/drivers/net/virtio/virtqueue.h index 7789411..a9410b4 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -237,6 +237,14 @@ struct virtio_net_hdr_mrg_rxbuf {
> uint16_t num_buffers; /**< Number of merged rx buffers */ };
>
> +/* Region reserved to allow for transmit header and indirect ring */
> +#define VIRTIO_MAX_TX_INDIRECT 8 struct virtio_tx_region {
> + struct virtio_net_hdr_mrg_rxbuf tx_hdr;
> + struct vring_desc tx_indir[VIRTIO_MAX_TX_INDIRECT]
> + __attribute__((__aligned__(16))); };
> +
> /**
> * Tell the backend not to interrupt us.
> */
> --
> 2.1.4
