Re: [dpdk-dev] [PATCH v2] vhost: support async copy free segmentations

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

> -----Original Message-----
> From: Fu, Patrick <patrick.fu@intel.com>
> Sent: Wednesday, July 15, 2020 7:15 PM
> To: dev@dpdk.org; maxime.coquelin@redhat.com; Xia, Chenbo
> <chenbo.xia@intel.com>
> Cc: Fu, Patrick <patrick.fu@intel.com>; Wang, Yinan <yinan.wang@intel.com>
> Subject: [PATCH v2] vhost: support async copy free segmentations
> 
> From: Patrick Fu <patrick.fu@intel.com>
> 
> Vhost async enqueue assumes that all async copies should break at packet
> boundary. i.e. if a packet is splited into multiple copy segments, the async engine
> should always report copy completion when entire packet is finished. This patch
> removes the assumption.
> 
> Fixes: cd6760da1076 ("vhost: introduce async enqueue for split ring")
> 
> Signed-off-by: Patrick Fu <patrick.fu@intel.com>
> ---
> v2:
>  - fix an issue that can stuck async poll when packets buffer is full
>  - rename a local variable to better reflect its usage
> 
>  lib/librte_vhost/vhost.h      |  3 +++
>  lib/librte_vhost/virtio_net.c | 17 ++++++++++++-----
>  2 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h index
> 8c01cee42..0f7212f88 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -46,6 +46,8 @@
> 
>  #define MAX_PKT_BURST 32
> 
> +#define ASYNC_MAX_POLL_SEG 255
> +
>  #define VHOST_MAX_ASYNC_IT (MAX_PKT_BURST * 2)  #define
> VHOST_MAX_ASYNC_VEC (BUF_VECTOR_MAX * 2)
> 
> @@ -225,6 +227,7 @@ struct vhost_virtqueue {
>  	uint64_t	*async_pending_info;
>  	uint16_t	async_pkts_idx;
>  	uint16_t	async_pkts_inflight_n;
> +	uint16_t	async_last_seg_n;
> 
>  	/* vq async features */
>  	bool		async_inorder;
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index
> 1d0be3dd4..17808ab29 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -1633,6 +1633,7 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid,
> uint16_t queue_id,
>  	struct vhost_virtqueue *vq;
>  	uint16_t n_pkts_cpl, n_pkts_put = 0, n_descs = 0;
>  	uint16_t start_idx, pkts_idx, vq_size;
> +	uint16_t n_inflight;
>  	uint64_t *async_pending_info;
> 
>  	VHOST_LOG_DATA(DEBUG, "(%d) %s\n", dev->vid, __func__); @@ -
> 1646,28 +1647,32 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid,
> uint16_t queue_id,
> 
>  	rte_spinlock_lock(&vq->access_lock);
> 
> +	n_inflight = vq->async_pkts_inflight_n;
>  	pkts_idx = vq->async_pkts_idx;
>  	async_pending_info = vq->async_pending_info;
>  	vq_size = vq->size;
>  	start_idx = virtio_dev_rx_async_get_info_idx(pkts_idx,
>  		vq_size, vq->async_pkts_inflight_n);
> 
> -	n_pkts_cpl =
> -		vq->async_ops.check_completed_copies(vid, queue_id, 0,
> count);
> +	n_pkts_cpl = vq->async_ops.check_completed_copies(vid, queue_id,
> +		0, ASYNC_MAX_POLL_SEG - vq->async_last_seg_n) +
> +		vq->async_last_seg_n;
> 
>  	rte_smp_wmb();
> 
> -	while (likely(((start_idx + n_pkts_put) & (vq_size - 1)) != pkts_idx)) {
> +	while (likely((n_pkts_put < count) && n_inflight)) {
>  		uint64_t info = async_pending_info[
>  			(start_idx + n_pkts_put) & (vq_size - 1)];
>  		uint64_t n_segs;
>  		n_pkts_put++;
> +		n_inflight--;
>  		n_descs += info & ASYNC_PENDING_INFO_N_MSK;
>  		n_segs = info >> ASYNC_PENDING_INFO_N_SFT;
> 
>  		if (n_segs) {
> -			if (!n_pkts_cpl || n_pkts_cpl < n_segs) {
> +			if (unlikely(n_pkts_cpl < n_segs)) {
>  				n_pkts_put--;
> +				n_inflight++;
>  				n_descs -= info &
> ASYNC_PENDING_INFO_N_MSK;
>  				if (n_pkts_cpl) {
>  					async_pending_info[
> @@ -1684,8 +1689,10 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid,
> uint16_t queue_id,
>  		}
>  	}
> 
> +	vq->async_last_seg_n = n_pkts_cpl;
> +
>  	if (n_pkts_put) {
> -		vq->async_pkts_inflight_n -= n_pkts_put;
> +		vq->async_pkts_inflight_n = n_inflight;
>  		__atomic_add_fetch(&vq->used->idx, n_descs,
> __ATOMIC_RELEASE);
> 
>  		vhost_vring_call_split(dev, vq);
> --
> 2.18.4

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