[3/5] vhost: prefetch descriptor after the read barrier
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Commit Message
This patch moves the prefetch after the available index
is read to avoid prefetching a descriptor not available yet.
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
lib/librte_vhost/virtio_net.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
@@ -794,7 +794,6 @@ virtio_dev_rx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
struct buf_vector buf_vec[BUF_VECTOR_MAX];
uint16_t avail_head;
- rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
avail_head = *((volatile uint16_t *)&vq->avail->idx);
/*
@@ -803,6 +802,8 @@ virtio_dev_rx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
*/
rte_smp_rmb();
+ rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
+
for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
uint32_t pkt_len = pkts[pkt_idx]->pkt_len + dev->vhost_hlen;
uint16_t nr_vec = 0;
@@ -1378,8 +1379,6 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
}
}
- rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
-
free_entries = *((volatile uint16_t *)&vq->avail->idx) -
vq->last_avail_idx;
if (free_entries == 0)
@@ -1391,6 +1390,8 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
*/
rte_smp_rmb();
+ rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
+
VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__);
count = RTE_MIN(count, MAX_PKT_BURST);