Re: [dpdk-dev] [PATCH v2 1/3] vhost: add unsafe API to drain pkts in async vhost

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 6/15/21 4:15 PM, Cheng Jiang wrote:
> Applications need to stop DMA transfers and finish all the in-flight
> pkts when in VM memory hot-plug case and async vhost is used. This
> patch is to provide an unsafe API to drain in-flight pkts which are
> submitted to DMA engine in vhost async data path.
> 
> Signed-off-by: Cheng Jiang <cheng1.jiang@intel.com>
> ---
>  lib/vhost/rte_vhost_async.h | 22 +++++++++
>  lib/vhost/version.map       |  3 ++
>  lib/vhost/virtio_net.c      | 90 +++++++++++++++++++++++++++----------
>  3 files changed, 92 insertions(+), 23 deletions(-)
> 
> diff --git a/lib/vhost/rte_vhost_async.h b/lib/vhost/rte_vhost_async.h
> index 6faa31f5ad..041f40cf04 100644
> --- a/lib/vhost/rte_vhost_async.h
> +++ b/lib/vhost/rte_vhost_async.h
> @@ -193,4 +193,26 @@ __rte_experimental
>  uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
>  		struct rte_mbuf **pkts, uint16_t count);
>  
> +/**
> + * This function checks async completion status and empty all pakcets
> + * for a specific vhost device queue. Packets which are inflight will
> + * be returned in an array.
> + *
> + * @note This function does not perform any locking
> + *
> + * @param vid
> + *  id of vhost device to enqueue data
> + * @param queue_id
> + *  queue id to enqueue data
> + * @param pkts
> + *  blank array to get return packet pointer
> + * @param count
> + *  size of the packet array
> + * @return
> + *  num of packets returned
> + */
> +__rte_experimental
> +uint16_t rte_vhost_drain_queue_thread_unsafe(int vid, uint16_t queue_id,
> +		struct rte_mbuf **pkts, uint16_t count);
> +
>  #endif /* _RTE_VHOST_ASYNC_H_ */
> diff --git a/lib/vhost/version.map b/lib/vhost/version.map
> index 9103a23cd4..f480f188af 100644
> --- a/lib/vhost/version.map
> +++ b/lib/vhost/version.map
> @@ -79,4 +79,7 @@ EXPERIMENTAL {
>  
>  	# added in 21.05
>  	rte_vhost_get_negotiated_protocol_features;
> +
> +	# added in 21.08
> +	rte_vhost_drain_queue_thread_unsafe;
>  };
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 8da8a86a10..793510974a 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2082,36 +2082,18 @@ write_back_completed_descs_packed(struct vhost_virtqueue *vq,
>  	} while (nr_left > 0);
>  }
>  
> -uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
> +static __rte_always_inline uint16_t
> +vhost_poll_enqueue_completed(struct virtio_net *dev, uint16_t queue_id,
>  		struct rte_mbuf **pkts, uint16_t count)
>  {
> -	struct virtio_net *dev = get_device(vid);
>  	struct vhost_virtqueue *vq;
>  	uint16_t n_pkts_cpl = 0, n_pkts_put = 0, n_descs = 0, n_buffers = 0;
>  	uint16_t start_idx, pkts_idx, vq_size;
>  	struct async_inflight_info *pkts_info;
>  	uint16_t from, i;
>  
> -	if (!dev)
> -		return 0;
> -
> -	VHOST_LOG_DATA(DEBUG, "(%d) %s\n", dev->vid, __func__);
> -	if (unlikely(!is_valid_virt_queue_idx(queue_id, 0, 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(!vq->async_registered)) {
> -		VHOST_LOG_DATA(ERR, "(%d) %s: async not registered for queue id %d.\n",
> -			dev->vid, __func__, queue_id);
> -		return 0;
> -	}
> -
> -	rte_spinlock_lock(&vq->access_lock);
> -
>  	pkts_idx = vq->async_pkts_idx % vq->size;
>  	pkts_info = vq->async_pkts_info;
>  	vq_size = vq->size;
> @@ -2119,14 +2101,14 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
>  		vq_size, vq->async_pkts_inflight_n);
>  
>  	if (count > vq->async_last_pkts_n)
> -		n_pkts_cpl = vq->async_ops.check_completed_copies(vid,
> +		n_pkts_cpl = vq->async_ops.check_completed_copies(dev->vid,
>  			queue_id, 0, count - vq->async_last_pkts_n);
>  	n_pkts_cpl += vq->async_last_pkts_n;
>  
>  	n_pkts_put = RTE_MIN(count, n_pkts_cpl);
>  	if (unlikely(n_pkts_put == 0)) {
>  		vq->async_last_pkts_n = n_pkts_cpl;
> -		goto done;
> +		return 0;
>  	}
>  
>  	if (vq_is_packed(dev)) {
> @@ -2165,12 +2147,74 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
>  			vq->last_async_desc_idx_split += n_descs;
>  	}
>  
> -done:
> +	return n_pkts_put;
> +}
> +
> +uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
> +		struct rte_mbuf **pkts, uint16_t count)
> +{
> +	struct virtio_net *dev = get_device(vid);
> +	struct vhost_virtqueue *vq;
> +	uint16_t n_pkts_put = 0;
> +
> +	if (!dev)
> +		return 0;
> +
> +	VHOST_LOG_DATA(DEBUG, "(%d) %s\n", dev->vid, __func__);
> +	if (unlikely(!is_valid_virt_queue_idx(queue_id, 0, 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(!vq->async_registered)) {
> +		VHOST_LOG_DATA(ERR, "(%d) %s: async not registered for queue id %d.\n",
> +			dev->vid, __func__, queue_id);
> +		return 0;
> +	}
> +
> +	rte_spinlock_lock(&vq->access_lock);
> +
> +	n_pkts_put = vhost_poll_enqueue_completed(dev, queue_id, pkts, count);
> +
>  	rte_spinlock_unlock(&vq->access_lock);
>  
>  	return n_pkts_put;
>  }
>  
> +uint16_t rte_vhost_drain_queue_thread_unsafe(int vid, uint16_t queue_id,
> +		struct rte_mbuf **pkts, uint16_t count)
> +{
> +	struct virtio_net *dev = get_device(vid);
> +	struct vhost_virtqueue *vq;
> +	uint16_t n_pkts = count;
> +
> +	if (!dev)
> +		return 0;
> +
> +	VHOST_LOG_DATA(DEBUG, "(%d) %s\n", dev->vid, __func__);
> +	if (unlikely(!is_valid_virt_queue_idx(queue_id, 0, 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(!vq->async_registered)) {
> +		VHOST_LOG_DATA(ERR, "(%d) %s: async not registered for queue id %d.\n",
> +			dev->vid, __func__, queue_id);
> +		return 0;
> +	}
> +
> +	while (count)
> +		count -= vhost_poll_enqueue_completed(dev, queue_id, pkts, count);

I think we may want to improve the sync_ops so that
.check_completed_copies() returns an int. If for some reason the DMA
driver callback fails, we would poll forever.

Looking more into the code, I see that ioat_check_completed_copies_cb()
an return -1 (whereas it should return an unint32_t). It would lead to
undefined behaviour if the failure would happen. The IOAT driver needs
to be fixed, and also the callback prototype and its handling.

> +
> +	return n_pkts;
> +}
> +
>  static __rte_always_inline uint32_t
>  virtio_dev_rx_async_submit(struct virtio_net *dev, uint16_t queue_id,
>  	struct rte_mbuf **pkts, uint32_t count,
>