Re: [dpdk-dev] [PATCH v2 1/4] vhost: support async dequeue for split ring

["Jiang, Cheng1" <cheng1.jiang@intel.com>]

Hi Wenwu,

Comments are inline.

> -----Original Message-----
> From: Ma, WenwuX <wenwux.ma@intel.com>
> Sent: Saturday, September 18, 2021 3:27 AM
> To: dev@dpdk.org
> Cc: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>;
> Jiang, Cheng1 <cheng1.jiang@intel.com>; Hu, Jiayu <jiayu.hu@intel.com>;
> Pai G, Sunil <sunil.pai.g@intel.com>; Yang, YvonneX
> <yvonnex.yang@intel.com>; Wang, YuanX <yuanx.wang@intel.com>; Ma,
> WenwuX <wenwux.ma@intel.com>; Wang, Yinan <yinan.wang@intel.com>
> Subject: [PATCH v2 1/4] vhost: support async dequeue for split ring
> 
> From: Yuan Wang <yuanx.wang@intel.com>
> 
> This patch implements asynchronous dequeue data path for split ring.
> A new asynchronous dequeue function is introduced. With this function, the
> application can try to receive packets from the guest with offloading copies
> to the async channel, thus saving precious CPU cycles.
> 
> Signed-off-by: Yuan Wang <yuanx.wang@intel.com>
> Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
> Signed-off-by: Wenwu Ma <wenwux.ma@intel.com>
> Tested-by: Yinan Wang <yinan.wang@intel.com>
> Tested-by: Yvonne Yang <yvonnex.yang@intel.com>
> ---
>  doc/guides/prog_guide/vhost_lib.rst |   9 +
>  lib/vhost/rte_vhost_async.h         |  33 +-
>  lib/vhost/version.map               |   3 +
>  lib/vhost/vhost.h                   |   3 +-
>  lib/vhost/virtio_net.c              | 530 ++++++++++++++++++++++++++++
>  5 files changed, 575 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst
> b/doc/guides/prog_guide/vhost_lib.rst
> index 171e0096f6..9ed544db7a 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -303,6 +303,15 @@ The following is an overview of some key Vhost API
> functions:
>    Clear inflight packets which are submitted to DMA engine in vhost async
> data
>    path. Completed packets are returned to applications through ``pkts``.
> 
> +* ``rte_vhost_async_try_dequeue_burst(vid, queue_id, mbuf_pool, pkts,
> +count, nr_inflight)``
> +
> +  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.
> +
>  Vhost-user Implementations
>  --------------------------
> 
> diff --git a/lib/vhost/rte_vhost_async.h b/lib/vhost/rte_vhost_async.h index
> ad71555a7f..973efa19b1 100644
> --- a/lib/vhost/rte_vhost_async.h
> +++ b/lib/vhost/rte_vhost_async.h
> @@ -84,11 +84,12 @@ struct rte_vhost_async_channel_ops {  };
> 
>  /**
> - * inflight async packet information
> + * in-flight async packet information
>   */
>  struct async_inflight_info {
>  	struct rte_mbuf *mbuf;
> -	uint16_t descs; /* num of descs inflight */
> +	struct virtio_net_hdr nethdr;
> +	uint16_t descs; /* num of descs in-flight */
>  	uint16_t nr_buffers; /* num of buffers inflight for packed ring */  };
> 
> @@ -255,5 +256,33 @@ int rte_vhost_async_get_inflight(int vid, uint16_t
> queue_id);  __rte_experimental  uint16_t
> rte_vhost_clear_queue_thread_unsafe(int vid, uint16_t queue_id,
>  		struct rte_mbuf **pkts, uint16_t count);

Blank line is needed here.

> +/**
> + * 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

The Initials should be in uppercase. The following also needs to be changed.

> + * @param queue_id
> + *  queue id to dequeue data

Should be 'ID of virtqueue ......'.

Thanks,
Cheng

> + * @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);
> 
>  #endif /* _RTE_VHOST_ASYNC_H_ */
> diff --git a/lib/vhost/version.map b/lib/vhost/version.map index
> c92a9d4962..1e033ad8e2 100644
> --- a/lib/vhost/version.map
> +++ b/lib/vhost/version.map
> @@ -85,4 +85,7 @@ EXPERIMENTAL {
>  	rte_vhost_async_channel_register_thread_unsafe;
>  	rte_vhost_async_channel_unregister_thread_unsafe;
>  	rte_vhost_clear_queue_thread_unsafe;
> +
> +	# added in 21.11
> +	rte_vhost_async_try_dequeue_burst;
>  };