Indirect descriptors are usually supported by virtio-net devices,
allowing to dispatch a larger number of requests.
When the virtio device sends a packet using indirect descriptors,
only one slot is used in the ring, even for large packets.
The main effect is to improve the 0% packet loss benchmark.
A PVP benchmark using Moongen (64 bytes) on the TE, and testpmd
(fwd io for host, macswap for VM) on DUT shows a +50% gain for
zero loss.
On the downside, micro-benchmark using testpmd txonly in VM and
rxonly on host shows a loss between 1 and 4%.i But depending on
the needs, feature can be disabled at VM boot time by passing
indirect_desc=off argument to vhost-user device in Qemu.
Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
---
Changes since v2:
-----------------
- Enrich commit message with figures
- Rebased on top of dpdk-next-virtio's master
- Add feature check to ensure we don't receive an indirect desc
if not supported by the virtio driver
lib/librte_vhost/vhost.c | 3 ++-
lib/librte_vhost/virtio_net.c | 38 +++++++++++++++++++++++++++++---------
2 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
index 46095c3..30bb0ce 100644
--- a/lib/librte_vhost/vhost.c
+++ b/lib/librte_vhost/vhost.c
@@ -65,7 +65,8 @@
(1ULL << VIRTIO_NET_F_CSUM) | \
(1ULL << VIRTIO_NET_F_GUEST_CSUM) | \
(1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
- (1ULL << VIRTIO_NET_F_GUEST_TSO6))
+ (1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
+ (1ULL << VIRTIO_RING_F_INDIRECT_DESC))
uint64_t VHOST_FEATURES = VHOST_SUPPORTED_FEATURES;
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 8a151af..0f7dd81 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -679,8 +679,8 @@ make_rarp_packet(struct rte_mbuf *rarp_mbuf, const struct
ether_addr *mac)
}
static inline int __attribute__((always_inline))
-copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
- struct rte_mbuf *m, uint16_t desc_idx,
+copy_desc_to_mbuf(struct virtio_net *dev, struct vring_desc *descs,
+ uint16_t max_desc, struct rte_mbuf *m, uint16_t desc_idx,
struct rte_mempool *mbuf_pool)
{
struct vring_desc *desc;
@@ -693,7 +693,7 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct
vhost_virtqueue *vq,
/* A counter to avoid desc dead loop chain */
uint32_t nr_desc = 1;
- desc = &vq->desc[desc_idx];
+ desc = &descs[desc_idx];
if (unlikely(desc->len < dev->vhost_hlen))
return -1;
@@ -711,7 +711,7 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct
vhost_virtqueue *vq,
*/
if (likely((desc->len == dev->vhost_hlen) &&
(desc->flags & VRING_DESC_F_NEXT) != 0)) {
- desc = &vq->desc[desc->next];
+ desc = &descs[desc->next];
desc_addr = gpa_to_vva(dev, desc->addr);
if (unlikely(!desc_addr))
@@ -747,10 +747,10 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct
vhost_virtqueue *vq,
if ((desc->flags & VRING_DESC_F_NEXT) == 0)
break;
- if (unlikely(desc->next >= vq->size ||
- ++nr_desc > vq->size))
+ if (unlikely(desc->next >= max_desc ||
+ ++nr_desc > max_desc))
return -1;
- desc = &vq->desc[desc->next];
+ desc = &descs[desc->next];
desc_addr = gpa_to_vva(dev, desc->addr);
if (unlikely(!desc_addr))
@@ -878,19 +878,39 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
/* Prefetch descriptor index. */
rte_prefetch0(&vq->desc[desc_indexes[0]]);
for (i = 0; i < count; i++) {
+ struct vring_desc *desc;
+ uint16_t sz, idx;
int err;
if (likely(i + 1 < count))
rte_prefetch0(&vq->desc[desc_indexes[i + 1]]);
+ if (vq->desc[desc_indexes[i]].flags & VRING_DESC_F_INDIRECT) {
+ if (unlikely(!(dev->features &
+ (1ULL <<
VIRTIO_RING_F_INDIRECT_DESC)))) {
+ RTE_LOG(ERR, VHOST_DATA,
+ "Indirect desc but feature not
negotiated.\n");
+ break;
+ }
+
+ desc = (struct vring_desc *)gpa_to_vva(dev,
+ vq->desc[desc_indexes[i]].addr);
+ rte_prefetch0(desc);
+ sz = vq->desc[desc_indexes[i]].len / sizeof(*desc);
+ idx = 0;
+ } else {
+ desc = vq->desc;
+ sz = vq->size;
+ idx = desc_indexes[i];
+ }
+
pkts[i] = rte_pktmbuf_alloc(mbuf_pool);
if (unlikely(pkts[i] == NULL)) {
RTE_LOG(ERR, VHOST_DATA,
"Failed to allocate memory for mbuf.\n");
break;
}
- err = copy_desc_to_mbuf(dev, vq, pkts[i], desc_indexes[i],
- mbuf_pool);
+ err = copy_desc_to_mbuf(dev, desc, sz, pkts[i], idx, mbuf_pool);
if (unlikely(err)) {
rte_pktmbuf_free(pkts[i]);
break;
--
2.7.4
