[dpdk-dev] [RFC PATCH 08/11] xxx: batch the desc_hw update?

[Jens Freimann <jfreiman@redhat.com>]

From: Yuanhan Liu <yuanhan.liu@linux.intel.com>

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

Conflicts:
	lib/librte_vhost/virtio_net.c
---
 drivers/net/virtio/virtio_rxtx_1.1.c | 18 ++++++++++--------
 lib/librte_vhost/virtio_net.c        | 17 ++++++++++-------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx_1.1.c b/drivers/net/virtio/virtio_rxtx_1.1.c
index e47a346..05f9dc7 100644
--- a/drivers/net/virtio/virtio_rxtx_1.1.c
+++ b/drivers/net/virtio/virtio_rxtx_1.1.c
@@ -89,7 +89,7 @@
 }
 
 static inline void
-virtio_xmit(struct virtnet_tx *txvq, struct rte_mbuf *mbuf)
+virtio_xmit(struct virtnet_tx *txvq, struct rte_mbuf *mbuf, int first_mbuf)
 {
 	struct virtio_tx_region *txr = txvq->virtio_net_hdr_mz->addr;
 	struct virtqueue *vq = txvq->vq;
@@ -105,6 +105,8 @@
 			  RTE_PTR_DIFF(&txr[idx].tx_hdr, txr);
 	desc[idx].len   = vq->hw->vtnet_hdr_size;
 	desc[idx].flags = VRING_DESC_F_NEXT;
+	if (!first_mbuf)
+		desc[idx].flags |= DESC_HW;
 
 	do {
 		idx = (vq->vq_avail_idx++) & (vq->vq_nentries - 1);
@@ -115,12 +117,6 @@
 
 	desc[idx].flags &= ~VRING_DESC_F_NEXT;
 
-	/*
-	 * update the head last, so that when the host saw such flag
-	 * is set, it means all others in the same chain is also set
-	 */
-	rte_smp_wmb();
-	desc[head_idx].flags |= DESC_HW;
 }
 
 uint16_t
@@ -129,6 +125,7 @@
 	struct virtnet_tx *txvq = tx_queue;
 	struct virtqueue *vq = txvq->vq;
 	uint16_t i;
+	uint16_t head_idx = vq->vq_avail_idx;
 
 	if (unlikely(nb_pkts < 1))
 		return nb_pkts;
@@ -148,10 +145,15 @@
 			}
 		}
 
-		virtio_xmit(txvq, txm);
+		virtio_xmit(txvq, txm, i == 0);
 		txvq->stats.bytes += txm->pkt_len;
 	}
 
+	if (likely(i)) {
+		rte_smp_wmb();
+		vq->vq_ring.desc_1_1[head_idx & (vq->vq_nentries - 1)].flags |= DESC_HW;
+	}
+
 	txvq->stats.packets += i;
 	txvq->stats.errors  += nb_pkts - i;
 
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index df88e31..c9e466f 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1009,9 +1009,6 @@ static inline bool __attribute__((always_inline))
 	 */
 	if (likely((desc->len == dev->vhost_hlen) &&
 		   (desc->flags & VRING_DESC_F_NEXT) != 0)) {
-		rte_smp_wmb();
-		desc->flags = 0;
-
 		desc = &descs[(head_idx++) & (vq->size - 1)];
 		if (unlikely(desc->flags & VRING_DESC_F_INDIRECT))
 			return -1;
@@ -1072,8 +1069,6 @@ static inline bool __attribute__((always_inline))
 			if ((desc->flags & VRING_DESC_F_NEXT) == 0)
 				break;
 
-			rte_smp_wmb();
-			desc->flags = 0;
 			desc = &descs[(head_idx++) & (vq->size - 1)];
 			if (unlikely(desc->flags & VRING_DESC_F_INDIRECT))
 				return -1;
@@ -1112,8 +1107,6 @@ static inline bool __attribute__((always_inline))
 			mbuf_avail  = cur->buf_len - RTE_PKTMBUF_HEADROOM;
 		}
 	}
-	rte_smp_wmb();
-	desc->flags = 0;
 
 	prev->data_len = mbuf_offset;
 	m->pkt_len    += mbuf_offset;
@@ -1134,7 +1127,9 @@ static inline bool __attribute__((always_inline))
 	uint16_t i;
 	uint16_t idx;
 	struct vring_desc_1_1 *desc = vq->desc_1_1;
+	uint16_t head_idx = vq->last_used_idx;
 
+	count = RTE_MIN(MAX_PKT_BURST, count);
 	for (i = 0; i < count; i++) {
 		idx = vq->last_used_idx & (vq->size - 1);
 		if (!(desc[idx].flags & DESC_HW))
@@ -1150,6 +1145,14 @@ static inline bool __attribute__((always_inline))
 		dequeue_desc(dev, vq, mbuf_pool, pkts[i], desc);
 	}
 
+	if (likely(i)) {
+		for (idx = 1; idx < (uint16_t)(vq->last_used_idx - head_idx); idx++) {
+			desc[(idx + head_idx) & (vq->size - 1)].flags = 0;
+		}
+		rte_smp_wmb();
+		desc[head_idx & (vq->size - 1)].flags = 0;
+	}
+
 	return i;
 }
 
-- 
1.8.3.1