vhost: improve batched copies performance

Instead of copying batch_copy_nb_elems into the stack,
this patch uses it directly.

Small performance gain of 3% is seen when running PVP
benchmark.

Acked-by: Zhihong Wang <zhihong.wang@intel.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index e66b8f4..98ad8e9 100644 (file)
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -352,7 +352,6 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
        struct rte_mbuf *hdr_mbuf;
        struct batch_copy_elem *batch_copy = vq->batch_copy_elems;
        struct virtio_net_hdr_mrg_rxbuf tmp_hdr, *hdr = NULL;
-       uint16_t copy_nb = vq->batch_copy_nb_elems;
        int error = 0;
 
        if (unlikely(m == NULL)) {
@@ -493,7 +492,8 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 
                cpy_len = RTE_MIN(desc_chunck_len, mbuf_avail);
 
-               if (likely(cpy_len > MAX_BATCH_LEN || copy_nb >= vq->size)) {
+               if (likely(cpy_len > MAX_BATCH_LEN ||
+                                       vq->batch_copy_nb_elems >= vq->size)) {
                        rte_memcpy((void *)((uintptr_t)(desc_addr +
                                                        desc_offset)),
                                rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
@@ -503,13 +503,14 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
                        PRINT_PACKET(dev, (uintptr_t)(desc_addr + desc_offset),
                                cpy_len, 0);
                } else {
-                       batch_copy[copy_nb].dst =
+                       batch_copy[vq->batch_copy_nb_elems].dst =
                                (void *)((uintptr_t)(desc_addr + desc_offset));
-                       batch_copy[copy_nb].src =
+                       batch_copy[vq->batch_copy_nb_elems].src =
                                rte_pktmbuf_mtod_offset(m, void *, mbuf_offset);
-                       batch_copy[copy_nb].log_addr = desc_gaddr + desc_offset;
-                       batch_copy[copy_nb].len = cpy_len;
-                       copy_nb++;
+                       batch_copy[vq->batch_copy_nb_elems].log_addr =
+                               desc_gaddr + desc_offset;
+                       batch_copy[vq->batch_copy_nb_elems].len = cpy_len;
+                       vq->batch_copy_nb_elems++;
                }
 
                mbuf_avail  -= cpy_len;
@@ -520,7 +521,6 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
        }
 
 out:
-       vq->batch_copy_nb_elems = copy_nb;
 
        return error;
 }
@@ -766,7 +766,6 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
        /* A counter to avoid desc dead loop chain */
        uint32_t nr_desc = 1;
        struct batch_copy_elem *batch_copy = vq->batch_copy_elems;
-       uint16_t copy_nb = vq->batch_copy_nb_elems;
        int error = 0;
 
        desc = &descs[desc_idx];
@@ -905,7 +904,7 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
                        mbuf_avail = cpy_len;
                } else {
                        if (likely(cpy_len > MAX_BATCH_LEN ||
-                                  copy_nb >= vq->size ||
+                                  vq->batch_copy_nb_elems >= vq->size ||
                                   (hdr && cur == m) ||
                                   desc->len != desc_chunck_len)) {
                                rte_memcpy(rte_pktmbuf_mtod_offset(cur, void *,
@@ -914,14 +913,15 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
                                                                desc_offset)),
                                           cpy_len);
                        } else {
-                               batch_copy[copy_nb].dst =
+                               batch_copy[vq->batch_copy_nb_elems].dst =
                                        rte_pktmbuf_mtod_offset(cur, void *,
                                                                mbuf_offset);
-                               batch_copy[copy_nb].src =
+                               batch_copy[vq->batch_copy_nb_elems].src =
                                        (void *)((uintptr_t)(desc_addr +
                                                             desc_offset));
-                               batch_copy[copy_nb].len = cpy_len;
-                               copy_nb++;
+                               batch_copy[vq->batch_copy_nb_elems].len =
+                                       cpy_len;
+                               vq->batch_copy_nb_elems++;
                        }
                }
 
@@ -1015,7 +1015,6 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
                vhost_dequeue_offload(hdr, m);
 
 out:
-       vq->batch_copy_nb_elems = copy_nb;
 
        return error;
 }