From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Coquelin Subject: [PATCH v2 3/4] vhost: prefetch descriptor after the read barrier Date: Wed, 19 Dec 2018 09:21:12 +0100 Message-ID: <20181219082113.24455-4-maxime.coquelin@redhat.com> References: <20181219082113.24455-1-maxime.coquelin@redhat.com> Cc: stable@dpdk.org, Maxime Coquelin To: dev@dpdk.org, i.maximets@samsung.com, tiwei.bie@intel.com, zhihong.wang@intel.com, jasowang@redhat.com, mst@redhat.com Return-path: In-Reply-To: <20181219082113.24455-1-maxime.coquelin@redhat.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" This patch moves the prefetch after the available index is read to avoid prefetching a descriptor not available yet. Signed-off-by: Maxime Coquelin --- 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 a9b1bc55f..a9be633de 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); -- 2.17.2