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authorMaxime Coquelin <maxime.coquelin@redhat.com>2018-10-23 12:07:10 +0200
committerFerruh Yigit <ferruh.yigit@intel.com>2018-10-26 22:14:06 +0200
commite988a6d84599f83321f8036dc45acf26a97ad7ea (patch)
treeaaa582ecd70d411727f29d790886a793400bfece /lib/librte_vhost
parente4845bb4a68513c477dd35fcdcb086681788be7d (diff)
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vhost: avoid memory barriers when no descriptors dequeued
In both split and packed dequeue paths, flush_shadow_used_ring and vhost_ring_call variants gets called even if not packets have been dequeued, and so no descriptors updates happened. It has an impact on CPU pipeline, as memory barriers are used in these functions. This patch don't call these functions if no descriptors have been dequeued. The performance gain with split ring when dequeue zero-copy is disabled should be null, but should be noticeable with packed ring or dequeue zero-copy enabled. Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring") Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path") Cc: stable@dpdk.org Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com> Reviewed-by: Jens Freimann <jfreimann@redhat.com> Tested-by: Jens Freimann <jfreimann@redhat.com> Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>
Diffstat (limited to 'lib/librte_vhost')
-rw-r--r--lib/librte_vhost/virtio_net.c24
1 files changed, 16 insertions, 8 deletions
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 1c31c05..8ad30c9 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1360,8 +1360,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
}
}
- flush_shadow_used_ring_split(dev, vq);
- vhost_vring_call_split(dev, vq);
+ if (likely(vq->shadow_used_idx)) {
+ flush_shadow_used_ring_split(dev, vq);
+ vhost_vring_call_split(dev, vq);
+ }
}
rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
@@ -1440,8 +1442,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
do_data_copy_dequeue(vq);
if (unlikely(i < count))
vq->shadow_used_idx = i;
- flush_shadow_used_ring_split(dev, vq);
- vhost_vring_call_split(dev, vq);
+ if (likely(vq->shadow_used_idx)) {
+ flush_shadow_used_ring_split(dev, vq);
+ vhost_vring_call_split(dev, vq);
+ }
}
return i;
@@ -1476,8 +1480,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
}
}
- flush_shadow_used_ring_packed(dev, vq);
- vhost_vring_call_packed(dev, vq);
+ if (likely(vq->shadow_used_idx)) {
+ flush_shadow_used_ring_packed(dev, vq);
+ vhost_vring_call_packed(dev, vq);
+ }
}
VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__);
@@ -1555,8 +1561,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
do_data_copy_dequeue(vq);
if (unlikely(i < count))
vq->shadow_used_idx = i;
- flush_shadow_used_ring_packed(dev, vq);
- vhost_vring_call_packed(dev, vq);
+ if (likely(vq->shadow_used_idx)) {
+ flush_shadow_used_ring_packed(dev, vq);
+ vhost_vring_call_packed(dev, vq);
+ }
}
return i;