Re: [dpdk-dev] [PATCH v2 2/3] vhost: rework async feature struct

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

Hi Jiayu,

On 7/7/21 1:18 PM, Jiayu Hu wrote:
> No need to use bitfields in the structure rte_vhost_async_features.
> This patch reworks the structure to improve code readability. In
> addition, add preserved padding fields on the structure for future
> usage.
> 
> Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
> ---
>  examples/vhost/main.c       |  4 ++--
>  lib/vhost/rte_vhost_async.h | 24 ++++++++----------------
>  lib/vhost/vhost.c           | 13 +++++--------
>  3 files changed, 15 insertions(+), 26 deletions(-)
> 
> diff --git a/examples/vhost/main.c b/examples/vhost/main.c
> index d2179ea..ec1a5b4 100644
> --- a/examples/vhost/main.c
> +++ b/examples/vhost/main.c
> @@ -1468,7 +1468,7 @@ new_device(int vid)
>  		vid, vdev->coreid);
>  
>  	if (async_vhost_driver) {
> -		struct rte_vhost_async_features f;
> +		struct rte_vhost_async_features f = {0};
>  		struct rte_vhost_async_channel_ops channel_ops;
>  
>  		if (dma_type != NULL && strncmp(dma_type, "ioat", 4) == 0) {
> @@ -1480,7 +1480,7 @@ new_device(int vid)
>  			f.async_threshold = 256;
>  
>  			return rte_vhost_async_channel_register(vid, VIRTIO_RXQ,
> -				f.intval, &channel_ops);
> +				f, &channel_ops);
>  		}
>  	}
>  
> diff --git a/lib/vhost/rte_vhost_async.h b/lib/vhost/rte_vhost_async.h
> index 6faa31f..12c6962 100644
> --- a/lib/vhost/rte_vhost_async.h
> +++ b/lib/vhost/rte_vhost_async.h
> @@ -93,18 +93,13 @@ struct async_inflight_info {
>  };
>  
>  /**
> - *  dma channel feature bit definition
> + *  dma channel features
>   */
>  struct rte_vhost_async_features {

Give the struct also contains config/tuning stuff, I don't think
rte_vhost_async_features is a good name, maybe rte_vhost_async_config?

> -	union {
> -		uint32_t intval;
> -		struct {
> -			uint32_t async_inorder:1;
> -			uint32_t resvd_0:15;
> -			uint32_t async_threshold:12;
> -			uint32_t resvd_1:4;
> -		};
> -	};
> +	uint32_t async_threshold;



> +	uint32_t resvd_0[13];

That's a lot of padding! I hope the application won't have to use that
much to configure the async feature one day :)

> +	uint8_t async_inorder;

I would prefer a uint32_t features bitfield for consistency with Vhost
library, with enums for the features definition.

> +	uint8_t resvd_1[7];
>  };
>  
>  /**
> @@ -115,11 +110,7 @@ struct rte_vhost_async_features {
>   * @param queue_id
>   *  vhost queue id async channel to be attached to
>   * @param features
> - *  DMA channel feature bit
> - *    b0       : DMA supports inorder data transfer
> - *    b1  - b15: reserved
> - *    b16 - b27: Packet length threshold for DMA transfer
> - *    b28 - b31: reserved
> + *  DMA channel feature structure
>   * @param ops
>   *  DMA operation callbacks
>   * @return
> @@ -127,7 +118,8 @@ struct rte_vhost_async_features {
>   */
>  __rte_experimental
>  int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
> -	uint32_t features, struct rte_vhost_async_channel_ops *ops);
> +	struct rte_vhost_async_features features,
> +	struct rte_vhost_async_channel_ops *ops);
>  
>  /**
>   * unregister a dma channel for vhost
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index 53a470f..835aad8 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -1620,18 +1620,15 @@ int rte_vhost_extern_callback_register(int vid,
>  }
>  
>  int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
> -					uint32_t features,
> -					struct rte_vhost_async_channel_ops *ops)
> +		struct rte_vhost_async_features features,
> +		struct rte_vhost_async_channel_ops *ops)
>  {
>  	struct vhost_virtqueue *vq;
>  	struct virtio_net *dev = get_device(vid);
> -	struct rte_vhost_async_features f;
>  
>  	if (dev == NULL || ops == NULL)
>  		return -1;
>  
> -	f.intval = features;
> -
>  	if (queue_id >= VHOST_MAX_VRING)
>  		return -1;
>  
> @@ -1640,7 +1637,7 @@ int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
>  	if (unlikely(vq == NULL || !dev->async_copy))
>  		return -1;
>  
> -	if (unlikely(!f.async_inorder)) {
> +	if (unlikely(!features.async_inorder)) {
>  		VHOST_LOG_CONFIG(ERR,
>  			"async copy is not supported on non-inorder mode "
>  			"(vid %d, qid: %d)\n", vid, queue_id);
> @@ -1720,8 +1717,8 @@ int rte_vhost_async_channel_register(int vid, uint16_t queue_id,
>  	vq->async_ops.check_completed_copies = ops->check_completed_copies;
>  	vq->async_ops.transfer_data = ops->transfer_data;
>  
> -	vq->async_inorder = f.async_inorder;
> -	vq->async_threshold = f.async_threshold;
> +	vq->async_inorder = features.async_inorder;
> +	vq->async_threshold = features.async_threshold;
>  
>  	vq->async_registered = true;
>  
>