[PATCH v2 1/3] vhost: remove redundant copy for packed shadow used ring

[Cheng Jiang <cheng1.jiang@intel.com>]

In the packed ring enqueue data path of the current asynchronous
Vhost design, the shadow used ring is first copied to the sync
shadow used ring, and then it will be moved to the async shadow
used ring for some historical reasons. This is completely unnecessary.
This patch removes redundant copy for the shadow used ring. The async
shadow used ring will be updated directly.

Signed-off-by: Cheng Jiang <cheng1.jiang@intel.com>
---
 lib/vhost/virtio_net.c | 66 ++++++++++++++++++++----------------------
 1 file changed, 31 insertions(+), 35 deletions(-)

diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index 9abf752f30..7c3ec128a0 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -572,6 +572,26 @@ vhost_shadow_enqueue_packed(struct vhost_virtqueue *vq,
 	}
 }
 
+static __rte_always_inline void
+vhost_async_shadow_enqueue_packed(struct vhost_virtqueue *vq,
+				   uint32_t *len,
+				   uint16_t *id,
+				   uint16_t *count,
+				   uint16_t num_buffers)
+{
+	uint16_t i;
+	struct vhost_async *async = vq->async;
+
+	for (i = 0; i < num_buffers; i++) {
+		async->buffers_packed[async->buffer_idx_packed].id  = id[i];
+		async->buffers_packed[async->buffer_idx_packed].len = len[i];
+		async->buffers_packed[async->buffer_idx_packed].count = count[i];
+		async->buffer_idx_packed++;
+		if (async->buffer_idx_packed >= vq->size)
+			async->buffer_idx_packed -= vq->size;
+	}
+}
+
 static __rte_always_inline void
 vhost_shadow_enqueue_single_packed(struct virtio_net *dev,
 				   struct vhost_virtqueue *vq,
@@ -1647,23 +1667,6 @@ store_dma_desc_info_split(struct vring_used_elem *s_ring, struct vring_used_elem
 	}
 }
 
-static __rte_always_inline void
-store_dma_desc_info_packed(struct vring_used_elem_packed *s_ring,
-		struct vring_used_elem_packed *d_ring,
-		uint16_t ring_size, uint16_t s_idx, uint16_t d_idx, uint16_t count)
-{
-	size_t elem_size = sizeof(struct vring_used_elem_packed);
-
-	if (d_idx + count <= ring_size) {
-		rte_memcpy(d_ring + d_idx, s_ring + s_idx, count * elem_size);
-	} else {
-		uint16_t size = ring_size - d_idx;
-
-		rte_memcpy(d_ring + d_idx, s_ring + s_idx, size * elem_size);
-		rte_memcpy(d_ring, s_ring + s_idx + size, (count - size) * elem_size);
-	}
-}
-
 static __rte_noinline uint32_t
 virtio_dev_rx_async_submit_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	struct rte_mbuf **pkts, uint32_t count, int16_t dma_id, uint16_t vchan_id)
@@ -1822,7 +1825,8 @@ vhost_enqueue_async_packed(struct virtio_net *dev,
 	if (unlikely(mbuf_to_desc(dev, vq, pkt, buf_vec, nr_vec, *nr_buffers, true) < 0))
 		return -1;
 
-	vhost_shadow_enqueue_packed(vq, buffer_len, buffer_buf_id, buffer_desc_count, *nr_buffers);
+	vhost_async_shadow_enqueue_packed(vq, buffer_len, buffer_buf_id,
+					buffer_desc_count, *nr_buffers);
 
 	return 0;
 }
@@ -1852,6 +1856,7 @@ dma_error_handler_packed(struct vhost_virtqueue *vq, uint16_t slot_idx,
 {
 	uint16_t descs_err = 0;
 	uint16_t buffers_err = 0;
+	struct vhost_async *async = vq->async;
 	struct async_inflight_info *pkts_info = vq->async->pkts_info;
 
 	*pkt_idx -= nr_err;
@@ -1869,7 +1874,10 @@ dma_error_handler_packed(struct vhost_virtqueue *vq, uint16_t slot_idx,
 		vq->avail_wrap_counter ^= 1;
 	}
 
-	vq->shadow_used_idx -= buffers_err;
+	if (async->buffer_idx_packed >= buffers_err)
+		async->buffer_idx_packed -= buffers_err;
+	else
+		async->buffer_idx_packed = async->buffer_idx_packed + vq->size - buffers_err;
 }
 
 static __rte_noinline uint32_t
@@ -1921,23 +1929,11 @@ virtio_dev_rx_async_submit_packed(struct virtio_net *dev, struct vhost_virtqueue
 		dma_error_handler_packed(vq, slot_idx, pkt_err, &pkt_idx);
 	}
 
-	if (likely(vq->shadow_used_idx)) {
-		/* keep used descriptors. */
-		store_dma_desc_info_packed(vq->shadow_used_packed, async->buffers_packed,
-					vq->size, 0, async->buffer_idx_packed,
-					vq->shadow_used_idx);
-
-		async->buffer_idx_packed += vq->shadow_used_idx;
-		if (async->buffer_idx_packed >= vq->size)
-			async->buffer_idx_packed -= vq->size;
-
-		async->pkts_idx += pkt_idx;
-		if (async->pkts_idx >= vq->size)
-			async->pkts_idx -= vq->size;
+	async->pkts_idx += pkt_idx;
+	if (async->pkts_idx >= vq->size)
+		async->pkts_idx -= vq->size;
 
-		vq->shadow_used_idx = 0;
-		async->pkts_inflight_n += pkt_idx;
-	}
+	async->pkts_inflight_n += pkt_idx;
 
 	return pkt_idx;
 }
-- 
2.35.1