vhost: improve prefetching in enqueue path

This is an optimization to prefetch next buffer while the
current one is being processed.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Tiwei Bie <tiwei.bie@intel.com>

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 2662a1d..82d5d9e 100644 (file)
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -393,6 +393,9 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
        buf_iova = buf_vec[vec_idx].buf_iova;
        buf_len = buf_vec[vec_idx].buf_len;
 
+       if (nr_vec > 1)
+               rte_prefetch0((void *)(uintptr_t)buf_vec[1].buf_addr);
+
        if (unlikely(buf_len < dev->vhost_hlen && nr_vec <= 1)) {
                error = -1;
                goto out;
@@ -404,7 +407,6 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
                hdr = &tmp_hdr;
        else
                hdr = (struct virtio_net_hdr_mrg_rxbuf *)(uintptr_t)hdr_addr;
-       rte_prefetch0((void *)(uintptr_t)hdr_addr);
 
        VHOST_LOG_DEBUG(VHOST_DATA, "(%d) RX: num merge buffers %d\n",
                dev->vid, num_buffers);
@@ -436,8 +438,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
                        buf_iova = buf_vec[vec_idx].buf_iova;
                        buf_len = buf_vec[vec_idx].buf_len;
 
-                       /* Prefetch buffer address. */
-                       rte_prefetch0((void *)(uintptr_t)buf_addr);
+                       /* Prefetch next buffer address. */
+                       if (vec_idx + 1 < nr_vec)
+                               rte_prefetch0((void *)(uintptr_t)
+                                               buf_vec[vec_idx + 1].buf_addr);
                        buf_offset = 0;
                        buf_avail  = buf_len;
                }
@@ -579,6 +583,8 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
                        break;
                }
 
+               rte_prefetch0((void *)(uintptr_t)buf_vec[0].buf_addr);
+
                VHOST_LOG_DEBUG(VHOST_DATA, "(%d) current index %d | end index %d\n",
                        dev->vid, vq->last_avail_idx,
                        vq->last_avail_idx + num_buffers);