From aaf8979d6fab6dc1742aee512275879a50d2084b Mon Sep 17 00:00:00 2001 From: Maxime Coquelin Date: Wed, 19 Dec 2018 09:21:12 +0100 Subject: [PATCH] vhost: prefetch descriptor after the read barrier This patch moves the prefetch after the available index is read to avoid prefetching a descriptor not available yet. Signed-off-by: Maxime Coquelin Acked-by: Michael S. Tsirkin Acked-by: Tiwei Bie --- lib/librte_vhost/virtio_net.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index a9b1bc55f6..a9be633deb 100644 --- a/lib/librte_vhost/virtio_net.c +++ b/lib/librte_vhost/virtio_net.c @@ -755,7 +755,6 @@ 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); /* @@ -764,6 +763,8 @@ 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; @@ -1339,8 +1340,6 @@ 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) @@ -1352,6 +1351,8 @@ 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); -- 2.20.1