Re: [RFC 1/2] vhost: add unsafe API to check inflight packets

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

Hi Xuan,

On 2/16/22 08:04, xuan.ding@intel.com wrote:
> From: Xuan Ding <xuan.ding@intel.com>
> 
> In async data path, when vring state changes or device is destroyed,
> it is necessary to know the number of inflight packets in DMA engine.
> This patch provides a thread unsafe API to return the number of
> inflight packets for a vhost queue without using any lock.
> 
> Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> ---
>   doc/guides/prog_guide/vhost_lib.rst    |  5 +++++
>   doc/guides/rel_notes/release_22_03.rst |  4 ++++
>   lib/vhost/rte_vhost_async.h            | 14 ++++++++++++++
>   lib/vhost/version.map                  |  1 +
>   lib/vhost/vhost.c                      | 26 ++++++++++++++++++++++++++
>   5 files changed, 50 insertions(+)
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
> index 886f8f5e72..f95288d128 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -271,6 +271,11 @@ The following is an overview of some key Vhost API functions:
>     This function returns the amount of in-flight packets for the vhost
>     queue using async acceleration.
>   
> + * ``rte_vhost_async_get_inflight_thread_unsafe(vid, queue_id)``
> +
> +  Get the number of inflight packets for a vhost queue without
> +  performing any locking.

Here and below in the API doc, I would add that it should only be used
within the vhost ops, which already hold the lock.

> +
>   * ``rte_vhost_clear_queue_thread_unsafe(vid, queue_id, **pkts, count, dma_id, vchan_id)``
>   
>     Clear inflight packets which are submitted to DMA engine in vhost async data
> diff --git a/doc/guides/rel_notes/release_22_03.rst b/doc/guides/rel_notes/release_22_03.rst
> index ff3095d742..37ef37bb20 100644
> --- a/doc/guides/rel_notes/release_22_03.rst
> +++ b/doc/guides/rel_notes/release_22_03.rst
> @@ -149,6 +149,10 @@ New Features
>     * Called ``rte_ipv4/6_udptcp_cksum_mbuf()`` functions in testpmd csum mode
>       to support software UDP/TCP checksum over multiple segments.
>   
> +* **Added vhost API to get the number of inflight packets.**
> +
> +  Added an API which can get the number of inflight packets in
> +  vhost async data path without using lock.
>   
>   Removed Items
>   -------------
> diff --git a/lib/vhost/rte_vhost_async.h b/lib/vhost/rte_vhost_async.h
> index 838c4778cc..06b0b0a579 100644
> --- a/lib/vhost/rte_vhost_async.h
> +++ b/lib/vhost/rte_vhost_async.h
> @@ -135,6 +135,20 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid, uint16_t queue_id,
>   __rte_experimental
>   int rte_vhost_async_get_inflight(int vid, uint16_t queue_id);
>   
> +/**
> + * This function is lock-free version to return the amount of in-flight
> + * packets for the vhost queue which uses async channel acceleration.
> + *
> + * @param vid
> + * id of vhost device to enqueue data
> + * @param queue_id
> + * queue id to enqueue data
> + * @return
> + * the amount of in-flight packets on success; -1 on failure
> + */
> +__rte_experimental
> +int rte_vhost_async_get_inflight_thread_unsafe(int vid, uint16_t queue_id);
> +
>   /**
>    * This function checks async completion status and clear packets for
>    * a specific vhost device queue. Packets which are inflight will be
> diff --git a/lib/vhost/version.map b/lib/vhost/version.map
> index 1202ba9c1a..03b46cb10e 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_get_inflight_thread_unsafe;

Don't forget to move it to "added in 22.07".

>   };
>   
>   INTERNAL {
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index 6bcb716de0..33dca62c6c 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -1907,6 +1907,32 @@ rte_vhost_async_get_inflight(int vid, uint16_t queue_id)
>   	return ret;
>   }
>   
> +int
> +rte_vhost_async_get_inflight_thread_unsafe(int vid, uint16_t queue_id)
> +{
> +	struct vhost_virtqueue *vq;
> +	struct virtio_net *dev = get_device(vid);
> +	int ret = -1;
> +
> +	if (dev == NULL)
> +		return ret;
> +
> +	if (queue_id >= VHOST_MAX_VRING)
> +		return ret;
> +
> +	vq = dev->virtqueue[queue_id];
> +
> +	if (vq == NULL)
> +		return ret;
> +
> +	if (!vq->async)
> +		return ret;
> +
> +	ret = vq->async->pkts_inflight_n;
> +
> +	return ret;
> +}
> +
>   int
>   rte_vhost_get_monitor_addr(int vid, uint16_t queue_id,
>   		struct rte_vhost_power_monitor_cond *pmc)