[dpdk-dev] [PATCH v4 5/6] vhost: batch update used ring

[Zhihong Wang]

This patch enables batch update of the used ring for better efficiency.

---
Changes in v4:

 1. Free shadow used ring in the right place.

 2. Add failure check for shadow used ring malloc.

Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
---
 lib/librte_vhost/vhost-net.h  |  4 +++
 lib/librte_vhost/vhost_rxtx.c | 62 ++++++++++++++++++++++++++++++++++++-------
 lib/librte_vhost/virtio-net.c | 42 ++++++++++++++++++++++++++---
 3 files changed, 95 insertions(+), 13 deletions(-)

diff --git a/lib/librte_vhost/vhost-net.h b/lib/librte_vhost/vhost-net.h
index 51fdf3d..a15182c 100644
--- a/lib/librte_vhost/vhost-net.h
+++ b/lib/librte_vhost/vhost-net.h
@@ -85,6 +85,10 @@ struct vhost_virtqueue {
 
 	/* Physical address of used ring, for logging */
 	uint64_t		log_guest_addr;
+
+	/* Shadow used ring for performance */
+	struct vring_used_elem	*shadow_used_ring;
+	uint32_t		shadow_used_idx;
 } __rte_cache_aligned;
 
 /* Old kernels have no such macro defined */
diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
index 927896c..ddc7b21 100644
--- a/lib/librte_vhost/vhost_rxtx.c
+++ b/lib/librte_vhost/vhost_rxtx.c
@@ -134,16 +134,51 @@ virtio_enqueue_offload(struct rte_mbuf *m_buf, struct virtio_net_hdr *net_hdr)
 }
 
 static inline void __attribute__((always_inline))
-update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
-		uint32_t desc_chain_head, uint32_t desc_chain_len)
+update_used_ring(struct vhost_virtqueue *vq, uint32_t desc_chain_head,
+		uint32_t desc_chain_len)
 {
-	uint32_t used_idx_round = vq->last_used_idx & (vq->size - 1);
+	vq->shadow_used_ring[vq->shadow_used_idx].id = desc_chain_head;
+	vq->shadow_used_ring[vq->shadow_used_idx].len = desc_chain_len;
+	vq->shadow_used_idx++;
+}
+
+static inline void __attribute__((always_inline))
+flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
+		uint32_t used_idx_start)
+{
+	if (used_idx_start + vq->shadow_used_idx < vq->size) {
+		rte_memcpy(&vq->used->ring[used_idx_start],
+				&vq->shadow_used_ring[0],
+				vq->shadow_used_idx *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[used_idx_start]),
+				vq->shadow_used_idx *
+				sizeof(struct vring_used_elem));
+	} else {
+		uint32_t part_1 = vq->size - used_idx_start;
+		uint32_t part_2 = vq->shadow_used_idx - part_1;
 
-	vq->used->ring[used_idx_round].id = desc_chain_head;
-	vq->used->ring[used_idx_round].len = desc_chain_len;
-	vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
-				ring[used_idx_round]),
-			sizeof(vq->used->ring[used_idx_round]));
+		rte_memcpy(&vq->used->ring[used_idx_start],
+				&vq->shadow_used_ring[0],
+				part_1 *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[used_idx_start]),
+				part_1 *
+				sizeof(struct vring_used_elem));
+		rte_memcpy(&vq->used->ring[0],
+				&vq->shadow_used_ring[part_1],
+				part_2 *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[0]),
+				part_2 *
+				sizeof(struct vring_used_elem));
+	}
 }
 
 static inline uint32_t __attribute__((always_inline))
@@ -208,7 +243,7 @@ enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
 					goto error;
 			} else if (is_mrg_rxbuf) {
 				/* start with the next desc chain */
-				update_used_ring(dev, vq, desc_chain_head,
+				update_used_ring(vq, desc_chain_head,
 						desc_chain_len);
 				vq->last_used_idx++;
 				extra_buffers++;
@@ -245,7 +280,7 @@ enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		desc_chain_len += copy_len;
 	}
 
-	update_used_ring(dev, vq, desc_chain_head, desc_chain_len);
+	update_used_ring(vq, desc_chain_head, desc_chain_len);
 	vq->last_used_idx++;
 
 	return 0;
@@ -276,6 +311,7 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 {
 	struct vhost_virtqueue *vq;
 	struct virtio_net *dev;
+	uint32_t used_idx_start;
 	uint32_t pkt_left = count;
 	uint32_t pkt_idx = 0;
 	uint32_t pkt_sent = 0;
@@ -302,6 +338,8 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 		is_mrg_rxbuf = 1;
 
 	/* start enqueuing packets 1 by 1 */
+	vq->shadow_used_idx = 0;
+	used_idx_start = vq->last_used_idx & (vq->size - 1);
 	avail_idx = *((volatile uint16_t *)&vq->avail->idx);
 	while (pkt_left && avail_idx != vq->last_used_idx) {
 		/* prefetch the next desc */
@@ -319,6 +357,10 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 		pkt_left--;
 	}
 
+	/* batch update used ring for better performance */
+	if (likely(vq->shadow_used_idx > 0))
+		flush_used_ring(dev, vq, used_idx_start);
+
 	/* update used idx and kick the guest if necessary */
 	if (pkt_sent)
 		notify_guest(dev, vq);
diff --git a/lib/librte_vhost/virtio-net.c b/lib/librte_vhost/virtio-net.c
index 1785695..7416079 100644
--- a/lib/librte_vhost/virtio-net.c
+++ b/lib/librte_vhost/virtio-net.c
@@ -152,10 +152,26 @@ cleanup_device(struct virtio_net *dev, int destroy)
 static void
 free_device(struct virtio_net *dev)
 {
+	struct vhost_virtqueue *vq_0;
+	struct vhost_virtqueue *vq_1;
 	uint32_t i;
 
-	for (i = 0; i < dev->virt_qp_nb; i++)
-		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
+	for (i = 0; i < dev->virt_qp_nb; i++) {
+		vq_0 = dev->virtqueue[i * VIRTIO_QNUM];
+		if (vq_0->shadow_used_ring) {
+			rte_free(vq_0->shadow_used_ring);
+			vq_0->shadow_used_ring = NULL;
+		}
+
+		vq_1 = dev->virtqueue[i * VIRTIO_QNUM + 1];
+		if (vq_1->shadow_used_ring) {
+			rte_free(vq_1->shadow_used_ring);
+			vq_1->shadow_used_ring = NULL;
+		}
+
+		/* malloc together, free together */
+		rte_free(vq_0);
+	}
 
 	rte_free(dev);
 }
@@ -418,13 +434,26 @@ int
 vhost_set_vring_num(int vid, struct vhost_vring_state *state)
 {
 	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
 
 	dev = get_device(vid);
 	if (dev == NULL)
 		return -1;
 
 	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
-	dev->virtqueue[state->index]->size = state->num;
+	vq = dev->virtqueue[state->index];
+	vq->size = state->num;
+	if (!vq->shadow_used_ring) {
+		vq->shadow_used_ring = rte_malloc(NULL,
+				vq->size * sizeof(struct vring_used_elem),
+				RTE_CACHE_LINE_SIZE);
+		if (!vq->shadow_used_ring) {
+			RTE_LOG(ERR, VHOST_CONFIG,
+				"Failed to allocate memory"
+				" for shadow used ring.\n");
+			return -1;
+		}
+	}
 
 	return 0;
 }
@@ -610,6 +639,7 @@ int
 vhost_get_vring_base(int vid, uint32_t index,
 	struct vhost_vring_state *state)
 {
+	struct vhost_virtqueue *vq;
 	struct virtio_net *dev;
 
 	dev = get_device(vid);
@@ -617,6 +647,12 @@ vhost_get_vring_base(int vid, uint32_t index,
 		return -1;
 
 	state->index = index;
+	vq = dev->virtqueue[state->index];
+	if (vq->shadow_used_ring) {
+		rte_free(vq->shadow_used_ring);
+		vq->shadow_used_ring = NULL;
+	}
+
 	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
 	state->num = dev->virtqueue[state->index]->last_used_idx;
 
-- 
2.7.4