[dpdk-dev] [PATCH v3] vhost: batch used descs chains write-back with packed ring
Maxime Coquelin
maxime.coquelin at redhat.com
Thu Dec 20 11:00:22 CET 2018
Instead of writing back descriptors chains in order, let's
write the first chain flags last in order to improve batching.
With Kernel's pktgen benchmark, ~3% performance gain is measured.
Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
lib/librte_vhost/virtio_net.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 8c657a101..66ccd3c35 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
{
int i;
uint16_t used_idx = vq->last_used_idx;
+ uint16_t head_idx = vq->last_used_idx;
+ uint16_t head_flags = 0;
/* Split loop in two to save memory barriers */
for (i = 0; i < vq->shadow_used_idx; i++) {
@@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
flags &= ~VRING_DESC_F_AVAIL;
}
- vq->desc_packed[vq->last_used_idx].flags = flags;
+ if (i > 0) {
+ vq->desc_packed[vq->last_used_idx].flags = flags;
- vhost_log_cache_used_vring(dev, vq,
+ vhost_log_cache_used_vring(dev, vq,
vq->last_used_idx *
sizeof(struct vring_packed_desc),
sizeof(struct vring_packed_desc));
+ } else {
+ head_idx = vq->last_used_idx;
+ head_flags = flags;
+ }
vq->last_used_idx += vq->shadow_used_packed[i].count;
if (vq->last_used_idx >= vq->size) {
@@ -140,7 +147,15 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
}
}
+ vq->desc_packed[head_idx].flags = head_flags;
+
rte_smp_wmb();
+
+ vhost_log_cache_used_vring(dev, vq,
+ head_idx *
+ sizeof(struct vring_packed_desc),
+ sizeof(struct vring_packed_desc));
+
vq->shadow_used_idx = 0;
vhost_log_cache_sync(dev, vq);
}
--
2.17.2
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