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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: dev@dpdk.org, jfreimann@redhat.com, tiwei.bie@intel.com,
	zhihong.wang@intel.com, jasowang@redhat.com
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: [dpdk-dev] [PATCH 3/5] vhost: prefetch descriptor after the read barrier
Date: Wed,  5 Dec 2018 10:49:55 +0100	[thread overview]
Message-ID: <20181205094957.1938-4-maxime.coquelin@redhat.com> (raw)
In-Reply-To: <20181205094957.1938-1-maxime.coquelin@redhat.com>

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(-)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 68b72e7a5..0a860ca72 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -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);
-- 
2.17.2

  parent reply	other threads:[~2018-12-05  9:50 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-05  9:49 [dpdk-dev] [PATCH 0/5] vhost: add missing barriers, remove useless volatiles Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 1/5] vhost: enforce avail index and desc read ordering Maxime Coquelin
     [not found]   ` <CGME20181205113041eucas1p1943b9c13af2fb5b736ba4906b59a9cd5@eucas1p1.samsung.com>
2018-12-05 11:30     ` [dpdk-dev] [1/5] " Ilya Maximets
2018-12-06  4:17       ` Jason Wang
2018-12-06 12:48         ` Ilya Maximets
2018-12-06 13:25           ` Jason Wang
2018-12-06 13:48         ` Michael S. Tsirkin
2018-12-07 14:58           ` Ilya Maximets
2018-12-07 15:44             ` Michael S. Tsirkin
     [not found]   ` <CGME20181211103848eucas1p10c270ca8997fea8a2f55c2d94d02baea@eucas1p1.samsung.com>
2018-12-11 10:38     ` Ilya Maximets
2018-12-11 14:46       ` Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 2/5] vhost: enforce desc flags and content " Maxime Coquelin
     [not found]   ` <CGME20181205133332eucas1p195b3864ed146403e314d7004d27be285@eucas1p1.samsung.com>
2018-12-05 13:33     ` [dpdk-dev] [2/5] " Ilya Maximets
2018-12-06  4:24       ` Jason Wang
2018-12-06 11:34         ` Ilya Maximets
2018-12-05  9:49 ` Maxime Coquelin [this message]
2018-12-05  9:49 ` [dpdk-dev] [PATCH 4/5] vhost: remove useless prefetch for packed ring descriptor Maxime Coquelin
2018-12-05  9:49 ` [dpdk-dev] [PATCH 5/5] vhost: remove useless casts to volatile Maxime Coquelin
     [not found]   ` <CGME20181205135231eucas1p1c89281f6525a0fedab4a2fc0d2e21393@eucas1p1.samsung.com>
2018-12-05 13:52     ` [dpdk-dev] [5/5] " Ilya Maximets
2018-12-06 16:59       ` Maxime Coquelin
2018-12-07 11:16         ` Ilya Maximets

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