[RFC 1/2] vhost: support async dequeue for split ring

[xuan.ding@intel.com]

From: Xuan Ding <xuan.ding@intel.com>

This patch implements asynchronous dequeue data path for vhost split
ring, with dmadev library integrated.

Signed-off-by: Yuan Wang <yuanx.wang@intel.com>
Signed-off-by: Xuan Ding <xuan.ding@intel.com>
---
 lib/vhost/rte_vhost_async.h |  29 +++
 lib/vhost/version.map       |   1 +
 lib/vhost/vhost.h           |   1 +
 lib/vhost/virtio_net.c      | 494 ++++++++++++++++++++++++++++++++++++
 4 files changed, 525 insertions(+)

diff --git a/lib/vhost/rte_vhost_async.h b/lib/vhost/rte_vhost_async.h
index 23a7a2d8b3..b1249382cd 100644
--- a/lib/vhost/rte_vhost_async.h
+++ b/lib/vhost/rte_vhost_async.h
@@ -203,4 +203,33 @@ __rte_experimental
 int rte_vhost_async_dma_configure(struct rte_vhost_async_dma_info *dmas,
 		uint16_t count);
 
+/**
+ * This function tries to receive packets from the guest with offloading
+ * copies to the async channel. The packets that are transfer completed
+ * are returned in "pkts". The other packets that their copies are submitted to
+ * the async channel but not completed are called "in-flight packets".
+ * This function will not return in-flight packets until their copies are
+ * completed by the async channel.
+ *
+ * @param vid
+ *  ID of vhost device to dequeue data
+ * @param queue_id
+ *  ID of virtqueue to dequeue data
+ * @param mbuf_pool
+ *  Mbuf_pool where host mbuf is allocated.
+ * @param pkts
+ *  Blank array to keep successfully dequeued packets
+ * @param count
+ *  Size of the packet array
+ * @param nr_inflight
+ *  The amount of in-flight packets. If error occurred, its value is set to -1.
+ * @return
+ *  Num of successfully dequeued packets
+ */
+__rte_experimental
+uint16_t
+rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
+	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count,
+	int *nr_inflight, uint16_t dma_id, uint16_t dma_vchan);
+
 #endif /* _RTE_VHOST_ASYNC_H_ */
diff --git a/lib/vhost/version.map b/lib/vhost/version.map
index 1202ba9c1a..816a6dc942 100644
--- a/lib/vhost/version.map
+++ b/lib/vhost/version.map
@@ -87,6 +87,7 @@ EXPERIMENTAL {
 
 	# added in 22.03
 	rte_vhost_async_dma_configure;
+	rte_vhost_async_try_dequeue_burst;
 };
 
 INTERNAL {
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index d9bda34e11..17166607ea 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -161,6 +161,7 @@ extern struct async_dma_info dma_copy_track[RTE_DMADEV_DEFAULT_MAX];
  */
 struct async_inflight_info {
 	struct rte_mbuf *mbuf;
+	struct virtio_net_hdr nethdr;
 	uint16_t descs; /* num of descs inflight */
 	uint16_t nr_buffers; /* num of buffers inflight for packed ring */
 };
diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index 9f81fc9733..148709f2c5 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -3092,3 +3092,497 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 
 	return count;
 }
+
+static __rte_always_inline int
+async_desc_to_mbuf_seg(struct virtio_net *dev, struct vhost_virtqueue *vq,
+			struct rte_mbuf *m, uint32_t mbuf_offset,
+			uint64_t buf_iova, uint32_t cpy_len)
+{
+	uint64_t mapped_len;
+	uint32_t buf_offset = 0;
+	void *hpa;
+
+	while (cpy_len) {
+		hpa = (void *)(uintptr_t)gpa_to_first_hpa(dev,
+					buf_iova + buf_offset, cpy_len,
+					&mapped_len);
+		if (unlikely(!hpa)) {
+			VHOST_LOG_DATA(ERR, "(%d) %s: failed to get hpa.\n",
+				dev->vid, __func__);
+			return -1;
+		}
+
+		if (unlikely(async_iter_add_iovec(vq->async, hpa,
+				(void *)(uintptr_t)rte_pktmbuf_iova_offset(m, mbuf_offset),
+				(size_t)mapped_len)))
+			return -1;
+
+		cpy_len -= (uint32_t)mapped_len;
+		mbuf_offset += (uint32_t)mapped_len;
+		buf_offset += (uint32_t)mapped_len;
+	}
+
+	return 0;
+}
+
+static __rte_always_inline int
+async_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
+		  struct buf_vector *buf_vec, uint16_t nr_vec,
+		  struct rte_mbuf *m, struct rte_mempool *mbuf_pool,
+		  struct virtio_net_hdr *nethdr)
+{
+	uint64_t buf_addr, buf_iova;
+	uint32_t buf_avail, buf_offset, buf_len;
+	uint32_t mbuf_avail, mbuf_offset;
+	uint32_t cpy_len;
+	/* A counter to avoid desc dead loop chain */
+	uint16_t vec_idx = 0;
+	struct rte_mbuf *cur = m, *prev = m;
+	struct virtio_net_hdr tmp_hdr;
+	struct virtio_net_hdr *hdr = NULL;
+	struct vhost_async *async = vq->async;
+
+	buf_addr = buf_vec[vec_idx].buf_addr;
+	buf_len = buf_vec[vec_idx].buf_len;
+	buf_iova = buf_vec[vec_idx].buf_iova;
+
+	if (unlikely(buf_len < dev->vhost_hlen && nr_vec <= 1))
+		return -1;
+
+	if (virtio_net_with_host_offload(dev)) {
+		if (unlikely(buf_len < sizeof(struct virtio_net_hdr))) {
+			/*
+			 * No luck, the virtio-net header doesn't fit
+			 * in a contiguous virtual area.
+			 */
+			copy_vnet_hdr_from_desc(&tmp_hdr, buf_vec);
+			hdr = &tmp_hdr;
+		} else {
+			hdr = (struct virtio_net_hdr *)((uintptr_t)buf_addr);
+		}
+	}
+
+	/*
+	 * A virtio driver normally uses at least 2 desc buffers
+	 * for Tx: the first for storing the header, and others
+	 * for storing the data.
+	 */
+	if (unlikely(buf_len < dev->vhost_hlen)) {
+		buf_offset = dev->vhost_hlen - buf_len;
+		vec_idx++;
+		buf_addr = buf_vec[vec_idx].buf_addr;
+		buf_iova = buf_vec[vec_idx].buf_iova;
+		buf_len = buf_vec[vec_idx].buf_len;
+		buf_avail  = buf_len - buf_offset;
+	} else if (buf_len == dev->vhost_hlen) {
+		if (unlikely(++vec_idx >= nr_vec))
+			return -1;
+		buf_addr = buf_vec[vec_idx].buf_addr;
+		buf_iova = buf_vec[vec_idx].buf_iova;
+		buf_len = buf_vec[vec_idx].buf_len;
+
+		buf_offset = 0;
+		buf_avail = buf_len;
+	} else {
+		buf_offset = dev->vhost_hlen;
+		buf_avail = buf_vec[vec_idx].buf_len - dev->vhost_hlen;
+	}
+
+	PRINT_PACKET(dev, (uintptr_t)(buf_addr + buf_offset), (uint32_t)buf_avail, 0);
+
+	mbuf_offset = 0;
+	mbuf_avail  = m->buf_len - RTE_PKTMBUF_HEADROOM;
+
+	if (async_iter_initialize(async))
+		return -1;
+
+	while (1) {
+		cpy_len = RTE_MIN(buf_avail, mbuf_avail);
+
+		if (async_desc_to_mbuf_seg(dev, vq, cur, mbuf_offset, buf_iova + buf_offset,
+					   cpy_len) < 0)
+			goto error;
+
+		mbuf_avail -= cpy_len;
+		buf_avail -= cpy_len;
+		mbuf_offset += cpy_len;
+		buf_offset += cpy_len;
+
+		/* This buf reaches to its end, get the next one */
+		if (buf_avail == 0) {
+			if (++vec_idx >= nr_vec)
+				break;
+
+			buf_addr = buf_vec[vec_idx].buf_addr;
+			buf_iova = buf_vec[vec_idx].buf_iova;
+			buf_len = buf_vec[vec_idx].buf_len;
+
+			buf_offset = 0;
+			buf_avail = buf_len;
+
+			PRINT_PACKET(dev, (uintptr_t)buf_addr, (uint32_t)buf_avail, 0);
+		}
+
+		/*
+		 * This mbuf reaches to its end, get a new one
+		 * to hold more data.
+		 */
+		if (mbuf_avail == 0) {
+			cur = rte_pktmbuf_alloc(mbuf_pool);
+			if (unlikely(cur == NULL)) {
+				VHOST_LOG_DATA(ERR,
+					"(%d) %s: failed to allocate memory for mbuf.\n",
+					dev->vid, __func__);
+				goto error;
+			}
+
+			prev->next = cur;
+			prev->data_len = mbuf_offset;
+			m->nb_segs += 1;
+			m->pkt_len += mbuf_offset;
+			prev = cur;
+
+			mbuf_offset = 0;
+			mbuf_avail = cur->buf_len - RTE_PKTMBUF_HEADROOM;
+		}
+	}
+
+	prev->data_len = mbuf_offset;
+	m->pkt_len += mbuf_offset;
+
+	async_iter_finalize(async);
+	if (hdr)
+		*nethdr = *hdr;
+
+	return 0;
+
+error:
+	async_iter_cancel(async);
+	return -1;
+}
+
+static __rte_always_inline uint16_t
+async_poll_dequeue_completed_split(struct virtio_net *dev, uint16_t queue_id,
+		struct rte_mbuf **pkts, uint16_t count, uint16_t dma_id, uint16_t dma_vchan,
+		bool legacy_ol_flags)
+{
+	uint16_t start_idx, from, i;
+	uint16_t nr_cpl_pkts = 0;
+	struct async_inflight_info *pkts_info;
+	struct vhost_virtqueue *vq = dev->virtqueue[queue_id];
+
+	pkts_info = vq->async->pkts_info;
+
+	vhost_async_dma_check_completed(dma_id, dma_vchan, count);
+
+	start_idx = async_get_first_inflight_pkt_idx(vq);
+
+	from = start_idx;
+	while (vq->async->pkts_cmpl_flag[from] && count--) {
+		vq->async->pkts_cmpl_flag[from] = false;
+		from = (from + 1) & (vq->size - 1);
+		nr_cpl_pkts++;
+	}
+
+	for (i = 0; i < nr_cpl_pkts; i++) {
+		from = (start_idx + i) & (vq->size - 1);
+		pkts[i] = pkts_info[from].mbuf;
+
+		if (virtio_net_with_host_offload(dev))
+			vhost_dequeue_offload(&pkts_info[from].nethdr, pkts[i], legacy_ol_flags);
+	}
+
+	/* write back completed descs to used ring and update used idx */
+	write_back_completed_descs_split(vq, nr_cpl_pkts);
+	__atomic_add_fetch(&vq->used->idx, nr_cpl_pkts, __ATOMIC_RELEASE);
+	vhost_vring_call_split(dev, vq);
+
+	vq->async->pkts_inflight_n -= nr_cpl_pkts;
+
+	return nr_cpl_pkts;
+}
+
+static __rte_always_inline uint16_t
+virtio_dev_tx_async_split(struct virtio_net *dev,	struct vhost_virtqueue *vq,
+		uint16_t queue_id, struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts,
+		uint16_t count, uint16_t dma_id, uint16_t dma_vchan, bool legacy_ol_flags)
+{
+	static bool allocerr_warned;
+	bool dropped = false;
+	uint16_t free_entries;
+	uint16_t pkt_idx, slot_idx = 0;
+	uint16_t nr_done_pkts = 0;
+	uint16_t pkt_err = 0;
+	int32_t n_xfer;
+	struct vhost_async *async = vq->async;
+	struct async_inflight_info *pkts_info = async->pkts_info;
+	struct rte_mbuf *pkts_prealloc[MAX_PKT_BURST];
+	uint16_t pkts_size = count;
+
+	/**
+	 * The ordering between avail index and
+	 * desc reads needs to be enforced.
+	 */
+	free_entries = __atomic_load_n(&vq->avail->idx, __ATOMIC_ACQUIRE) - vq->last_avail_idx;
+	if (free_entries == 0)
+		goto out;
+
+	rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
+
+	async_iter_reset(async);
+
+	count = RTE_MIN(count, MAX_PKT_BURST);
+	count = RTE_MIN(count, free_entries);
+	VHOST_LOG_DATA(DEBUG, "(%d) about to dequeue %u buffers\n", dev->vid, count);
+
+	if (rte_pktmbuf_alloc_bulk(mbuf_pool, pkts_prealloc, count))
+		goto out;
+
+	for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
+		uint16_t head_idx = 0;
+		uint16_t nr_vec = 0;
+		uint16_t to;
+		uint32_t buf_len;
+		int err;
+		struct buf_vector buf_vec[BUF_VECTOR_MAX];
+		struct rte_mbuf *pkt = pkts_prealloc[pkt_idx];
+
+		if (unlikely(fill_vec_buf_split(dev, vq, vq->last_avail_idx,
+						&nr_vec, buf_vec,
+						&head_idx, &buf_len,
+						VHOST_ACCESS_RO) < 0)) {
+			dropped = true;
+			break;
+		}
+
+		err = virtio_dev_pktmbuf_prep(dev, pkt, buf_len);
+		if (unlikely(err)) {
+			/**
+			 * mbuf allocation fails for jumbo packets when external
+			 * buffer allocation is not allowed and linear buffer
+			 * is required. Drop this packet.
+			 */
+			if (!allocerr_warned) {
+				VHOST_LOG_DATA(ERR,
+					"(%d) %s: Failed mbuf alloc of size %d from %s on %s.\n",
+					dev->vid, __func__, buf_len, mbuf_pool->name, dev->ifname);
+				allocerr_warned = true;
+			}
+			dropped = true;
+			break;
+		}
+
+		slot_idx = (async->pkts_idx + pkt_idx) & (vq->size - 1);
+		err = async_desc_to_mbuf(dev, vq, buf_vec, nr_vec, pkt, mbuf_pool,
+					&pkts_info[slot_idx].nethdr);
+		if (unlikely(err)) {
+			if (!allocerr_warned) {
+				VHOST_LOG_DATA(ERR,
+					"(%d) %s: Failed to offload copies to async channel %s.\n",
+					dev->vid, __func__, dev->ifname);
+				allocerr_warned = true;
+			}
+			dropped = true;
+			break;
+		}
+
+		pkts_info[slot_idx].mbuf = pkt;
+
+		/* store used descs */
+		to = async->desc_idx_split & (vq->size - 1);
+		async->descs_split[to].id = head_idx;
+		async->descs_split[to].len = 0;
+		async->desc_idx_split++;
+
+		vq->last_avail_idx++;
+	}
+
+	if (unlikely(dropped))
+		rte_pktmbuf_free_bulk(&pkts_prealloc[pkt_idx], count - pkt_idx);
+
+	n_xfer = vhost_async_dma_transfer(vq, dma_id, dma_vchan, async->pkts_idx, async->iov_iter,
+			pkt_idx);
+
+	async->pkts_inflight_n += n_xfer;
+
+	pkt_err = pkt_idx - n_xfer;
+	if (unlikely(pkt_err)) {
+		VHOST_LOG_DATA(DEBUG,
+			"(%d) %s: failed to transfer data for queue id %d.\n",
+			dev->vid, __func__, queue_id);
+
+		pkt_idx = n_xfer;
+		/* recover available ring */
+		vq->last_avail_idx -= pkt_err;
+
+		/**
+		 * recover async channel copy related structures and free pktmbufs
+		 * for error pkts.
+		 */
+		async->desc_idx_split -= pkt_err;
+		while (pkt_err-- > 0) {
+			rte_pktmbuf_free(pkts_info[slot_idx & (vq->size - 1)].mbuf);
+			slot_idx--;
+		}
+	}
+
+	async->pkts_idx += pkt_idx;
+	if (async->pkts_idx >= vq->size)
+		async->pkts_idx -= vq->size;
+
+out:
+	if (async->pkts_inflight_n > 0) {
+		nr_done_pkts = async_poll_dequeue_completed_split(dev, queue_id, pkts, pkts_size,
+					dma_id, dma_vchan, legacy_ol_flags);
+	}
+
+	return nr_done_pkts;
+}
+
+__rte_noinline
+static uint16_t
+virtio_dev_tx_async_split_legacy(struct virtio_net *dev,
+		struct vhost_virtqueue *vq, uint16_t queue_id,
+		struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts,
+		uint16_t count, uint16_t dma_id, uint16_t dma_vchan)
+{
+	return virtio_dev_tx_async_split(dev, vq, queue_id, mbuf_pool,
+				pkts, count, dma_id, dma_vchan, true);
+}
+
+__rte_noinline
+static uint16_t
+virtio_dev_tx_async_split_compliant(struct virtio_net *dev,
+		struct vhost_virtqueue *vq, uint16_t queue_id,
+		struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts,
+		uint16_t count, uint16_t dma_id, uint16_t dma_vchan)
+{
+	return virtio_dev_tx_async_split(dev, vq, queue_id, mbuf_pool,
+				pkts, count, dma_id, dma_vchan, false);
+}
+
+uint16_t
+rte_vhost_async_try_dequeue_burst(int vid, uint16_t queue_id,
+	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count,
+	int *nr_inflight, uint16_t dma_id, uint16_t dma_vchan)
+{
+	struct virtio_net *dev;
+	struct rte_mbuf *rarp_mbuf = NULL;
+	struct vhost_virtqueue *vq;
+	int16_t success = 1;
+
+	*nr_inflight = -1;
+
+	dev = get_device(vid);
+	if (!dev)
+		return 0;
+
+	if (unlikely(!(dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET))) {
+		VHOST_LOG_DATA(ERR,
+			"(%d) %s: built-in vhost net backend is disabled.\n",
+			dev->vid, __func__);
+		return 0;
+	}
+
+	if (unlikely(!is_valid_virt_queue_idx(queue_id, 1, dev->nr_vring))) {
+		VHOST_LOG_DATA(ERR,
+			"(%d) %s: invalid virtqueue idx %d.\n",
+			dev->vid, __func__, queue_id);
+		return 0;
+	}
+
+	vq = dev->virtqueue[queue_id];
+
+	if (unlikely(rte_spinlock_trylock(&vq->access_lock) == 0))
+		return 0;
+
+	if (unlikely(vq->enabled == 0)) {
+		count = 0;
+		goto out_access_unlock;
+	}
+
+	if (unlikely(!vq->async)) {
+		VHOST_LOG_DATA(ERR, "(%d) %s: async not registered for queue id %d.\n",
+			dev->vid, __func__, queue_id);
+		count = 0;
+		goto out_access_unlock;
+	}
+
+	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
+		vhost_user_iotlb_rd_lock(vq);
+
+	if (unlikely(vq->access_ok == 0))
+		if (unlikely(vring_translate(dev, vq) < 0)) {
+			count = 0;
+			goto out;
+		}
+
+	/*
+	 * Construct a RARP broadcast packet, and inject it to the "pkts"
+	 * array, to looks like that guest actually send such packet.
+	 *
+	 * Check user_send_rarp() for more information.
+	 *
+	 * broadcast_rarp shares a cacheline in the virtio_net structure
+	 * with some fields that are accessed during enqueue and
+	 * __atomic_compare_exchange_n causes a write if performed compare
+	 * and exchange. This could result in false sharing between enqueue
+	 * and dequeue.
+	 *
+	 * Prevent unnecessary false sharing by reading broadcast_rarp first
+	 * and only performing compare and exchange if the read indicates it
+	 * is likely to be set.
+	 */
+	if (unlikely(__atomic_load_n(&dev->broadcast_rarp, __ATOMIC_ACQUIRE) &&
+			__atomic_compare_exchange_n(&dev->broadcast_rarp,
+			&success, 0, 0, __ATOMIC_RELEASE, __ATOMIC_RELAXED))) {
+
+		rarp_mbuf = rte_net_make_rarp_packet(mbuf_pool, &dev->mac);
+		if (rarp_mbuf == NULL) {
+			VHOST_LOG_DATA(ERR, "Failed to make RARP packet.\n");
+			count = 0;
+			goto out;
+		}
+		count -= 1;
+	}
+
+	if (unlikely(vq_is_packed(dev))) {
+		static bool not_support_pack_log;
+		if (!not_support_pack_log) {
+			VHOST_LOG_DATA(ERR,
+				"(%d) %s: async dequeue does not support packed ring.\n",
+				dev->vid, __func__);
+			not_support_pack_log = true;
+		}
+		count = 0;
+		goto out;
+	}
+
+	if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
+		count = virtio_dev_tx_async_split_legacy(dev, vq, queue_id,
+				mbuf_pool, pkts, count, dma_id, dma_vchan);
+	else
+		count = virtio_dev_tx_async_split_compliant(dev, vq, queue_id,
+				mbuf_pool, pkts, count, dma_id, dma_vchan);
+
+	*nr_inflight = vq->async->pkts_inflight_n;
+
+out:
+	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
+		vhost_user_iotlb_rd_unlock(vq);
+
+out_access_unlock:
+	rte_spinlock_unlock(&vq->access_lock);
+
+	if (unlikely(rarp_mbuf != NULL)) {
+		/*
+		 * Inject it to the head of "pkts" array, so that switch's mac
+		 * learning table will get updated first.
+		 */
+		memmove(&pkts[1], pkts, count * sizeof(struct rte_mbuf *));
+		pkts[0] = rarp_mbuf;
+		count += 1;
+	}
+
+	return count;
+}
-- 
2.17.1