Re: [dpdk-dev] [PATCH v2 05/15] vhost: remove async batch threshold

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Wednesday, October 27, 2021 12:29 AM
> To: dev@dpdk.org; Xia, Chenbo <chenbo.xia@intel.com>; Hu, Jiayu
> <jiayu.hu@intel.com>; Wang, YuanX <yuanx.wang@intel.com>; Ma, WenwuX
> <wenwux.ma@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>;
> Mcnamara, John <john.mcnamara@intel.com>
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [PATCH v2 05/15] vhost: remove async batch threshold
> 
> Reaching the async batch threshold was one of the condition
> to trigger the DMA transfer. However, this condition was
> never met since the threshold value is 32, same as the
> MAX_PKT_BURST value.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/vhost/virtio_net.c | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index f0d923704a..c4a8b5276f 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -25,8 +25,6 @@
> 
>  #define MAX_BATCH_LEN 256
> 
> -#define VHOST_ASYNC_BATCH_THRESHOLD 32
> -
>  static  __rte_always_inline bool
>  rxvq_is_mergeable(struct virtio_net *dev)
>  {
> @@ -1565,12 +1563,10 @@ virtio_dev_rx_async_submit_split(struct virtio_net
> *dev,
>  		vq->last_avail_idx += num_buffers;
> 
>  		/*
> -		 * conditions to trigger async device transfer:
> -		 * - buffered packet number reaches transfer threshold
> +		 * condition to trigger async device transfer:
>  		 * - unused async iov number is less than max vhost vector
>  		 */
> -		if (unlikely(pkt_burst_idx >= VHOST_ASYNC_BATCH_THRESHOLD ||
> -			(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX))) {
> +		if (unlikely(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX)) {
>  			n_xfer = async->ops.transfer_data(dev->vid,
>  					queue_id, tdes, 0, pkt_burst_idx);
>  			if (likely(n_xfer >= 0)) {
> @@ -1864,12 +1860,10 @@ virtio_dev_rx_async_submit_packed(struct virtio_net
> *dev,
>  		vq_inc_last_avail_packed(vq, num_descs);
> 
>  		/*
> -		 * conditions to trigger async device transfer:
> -		 * - buffered packet number reaches transfer threshold
> +		 * condition to trigger async device transfer:
>  		 * - unused async iov number is less than max vhost vector
>  		 */
> -		if (unlikely(pkt_burst_idx >= VHOST_ASYNC_BATCH_THRESHOLD ||
> -			(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX))) {
> +		if (unlikely(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX)) {
>  			n_xfer = async->ops.transfer_data(dev->vid,
>  					queue_id, tdes, 0, pkt_burst_idx);
>  			if (likely(n_xfer >= 0)) {
> --
> 2.31.1

Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>