From: Maxime Coquelin Date: Tue, 27 Sep 2016 08:42:49 +0000 (+0200) Subject: vhost: support indirect Tx descriptors X-Git-Tag: spdx-start~5920 X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=2304dd73d287cc8ce30fdd9abd2f99f6af890dd4;p=dpdk.git vhost: support indirect Tx descriptors 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%. 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 Acked-by: Yuanhan Liu --- diff --git a/doc/guides/rel_notes/release_16_11.rst b/doc/guides/rel_notes/release_16_11.rst index a9a6095e7a..cc4b4d767a 100644 --- a/doc/guides/rel_notes/release_16_11.rst +++ b/doc/guides/rel_notes/release_16_11.rst @@ -36,6 +36,18 @@ New Features This section is a comment. Make sure to start the actual text at the margin. +* **Added vhost-user indirect descriptors support.** + + If indirect descriptor feature is negotiated, each packet sent by the guest + will take exactly one slot in the enqueue virtqueue. Without the feature, in + current version, even 64 bytes packets take two slots with Virtio PMD on guest + side. + + The main impact is better performance for 0% packet loss use-cases, as it + behaves as if the virtqueue size was enlarged, so more packets can be buffered + in case of system perturbations. On the downside, small performance degradation + is measured when running micro-benchmarks. + Resolved Issues --------------- diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c index 46095c3349..30bb0ce8ee 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 8a151afd94..a59c39bb94 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; @@ -693,8 +693,9 @@ 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]; - if (unlikely(desc->len < dev->vhost_hlen)) + desc = &descs[desc_idx]; + if (unlikely((desc->len < dev->vhost_hlen)) || + (desc->flags & VRING_DESC_F_INDIRECT)) return -1; desc_addr = gpa_to_vva(dev, desc->addr); @@ -711,7 +712,9 @@ 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]; + if (unlikely(desc->flags & VRING_DESC_F_INDIRECT)) + return -1; desc_addr = gpa_to_vva(dev, desc->addr); if (unlikely(!desc_addr)) @@ -747,10 +750,12 @@ 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 = &descs[desc->next]; + if (unlikely(desc->flags & VRING_DESC_F_INDIRECT)) return -1; - desc = &vq->desc[desc->next]; desc_addr = gpa_to_vva(dev, desc->addr); if (unlikely(!desc_addr)) @@ -878,19 +883,35 @@ 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) { + desc = (struct vring_desc *)(uintptr_t)gpa_to_vva(dev, + vq->desc[desc_indexes[i]].addr); + if (unlikely(!desc)) + break; + + 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;