[dpdk-dev] [PATCH v5 5/6] vhost: batch update used ring

[Maxime Coquelin]

On 09/09/2016 05:39 AM, Zhihong Wang wrote:
> This patch enables batch update of the used ring for better efficiency.
>
> Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
> ---
> Changes in v4:
>
>  1. Free shadow used ring in the right place.
>
>  2. Add failure check for shadow used ring malloc.
>
>  lib/librte_vhost/vhost.c      | 20 ++++++++++++--
>  lib/librte_vhost/vhost.h      |  4 +++
>  lib/librte_vhost/vhost_user.c | 31 +++++++++++++++++----
>  lib/librte_vhost/virtio_net.c | 64 +++++++++++++++++++++++++++++++++++--------
>  4 files changed, 101 insertions(+), 18 deletions(-)
>
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 46095c3..cb31cdd 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -119,10 +119,26 @@ cleanup_device(struct virtio_net *dev, int destroy)
>  static void
>  free_device(struct virtio_net *dev)
>  {
> +	struct vhost_virtqueue *vq_0;
> +	struct vhost_virtqueue *vq_1;
>  	uint32_t i;
>
> -	for (i = 0; i < dev->virt_qp_nb; i++)
> -		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
> +	for (i = 0; i < dev->virt_qp_nb; i++) {
> +		vq_0 = dev->virtqueue[i * VIRTIO_QNUM];
> +		if (vq_0->shadow_used_ring) {
> +			rte_free(vq_0->shadow_used_ring);
> +			vq_0->shadow_used_ring = NULL;
> +		}
> +
> +		vq_1 = dev->virtqueue[i * VIRTIO_QNUM + 1];
> +		if (vq_1->shadow_used_ring) {
> +			rte_free(vq_1->shadow_used_ring);
> +			vq_1->shadow_used_ring = NULL;
> +		}
> +
> +		/* malloc together, free together */
> +		rte_free(vq_0);
> +	}
>
>  	rte_free(dev);
>  }
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 9707dfc..381dc27 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -85,6 +85,10 @@ struct vhost_virtqueue {
>
>  	/* Physical address of used ring, for logging */
>  	uint64_t		log_guest_addr;
> +
> +	/* Shadow used ring for performance */
> +	struct vring_used_elem	*shadow_used_ring;
> +	uint32_t		shadow_used_idx;
>  } __rte_cache_aligned;
>
>  /* Old kernels have no such macro defined */
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index eee99e9..d7cf1ed 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -193,7 +193,21 @@ static int
>  vhost_user_set_vring_num(struct virtio_net *dev,
>  			 struct vhost_vring_state *state)
>  {
> -	dev->virtqueue[state->index]->size = state->num;
> +	struct vhost_virtqueue *vq;
> +
> +	vq = dev->virtqueue[state->index];
> +	vq->size = state->num;
> +	if (!vq->shadow_used_ring) {
> +		vq->shadow_used_ring = rte_malloc(NULL,
> +				vq->size * sizeof(struct vring_used_elem),
> +				RTE_CACHE_LINE_SIZE);
> +		if (!vq->shadow_used_ring) {
> +			RTE_LOG(ERR, VHOST_CONFIG,
> +				"Failed to allocate memory"
> +				" for shadow used ring.\n");
> +			return -1;
> +		}
> +	}
>
>  	return 0;
>  }
> @@ -611,14 +625,21 @@ static int
>  vhost_user_get_vring_base(struct virtio_net *dev,
>  			  struct vhost_vring_state *state)
>  {
> +	struct vhost_virtqueue *vq;
> +
>  	/* We have to stop the queue (virtio) if it is running. */
>  	if (dev->flags & VIRTIO_DEV_RUNNING) {
>  		dev->flags &= ~VIRTIO_DEV_RUNNING;
>  		notify_ops->destroy_device(dev->vid);
>  	}
>
> +	vq = dev->virtqueue[state->index];
>  	/* Here we are safe to get the last used index */
> -	state->num = dev->virtqueue[state->index]->last_used_idx;
> +	state->num = vq->last_used_idx;
> +	if (vq->shadow_used_ring) {
> +		rte_free(vq->shadow_used_ring);
> +		vq->shadow_used_ring = NULL;
> +	}
>
>  	RTE_LOG(INFO, VHOST_CONFIG,
>  		"vring base idx:%d file:%d\n", state->index, state->num);
> @@ -627,10 +648,10 @@ vhost_user_get_vring_base(struct virtio_net *dev,
>  	 * sent and only sent in vhost_vring_stop.
>  	 * TODO: cleanup the vring, it isn't usable since here.
>  	 */
> -	if (dev->virtqueue[state->index]->kickfd >= 0)
> -		close(dev->virtqueue[state->index]->kickfd);
> +	if (vq->kickfd >= 0)
> +		close(vq->kickfd);
>
> -	dev->virtqueue[state->index]->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
> +	vq->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
>
>  	return 0;
>  }
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index b38f18f..e9f6353 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -134,17 +134,52 @@ virtio_enqueue_offload(struct rte_mbuf *m_buf, struct virtio_net_hdr *net_hdr)
>  }
>
>  static inline void __attribute__((always_inline))
> -update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
> -		uint32_t desc_chain_head, uint32_t desc_chain_len)
> +update_used_ring(struct vhost_virtqueue *vq, uint32_t desc_chain_head,
> +		uint32_t desc_chain_len)
>  {
> -	uint32_t used_idx = vq->last_used_idx & (vq->size - 1);
> -
> -	vq->used->ring[used_idx].id = desc_chain_head;
> -	vq->used->ring[used_idx].len = desc_chain_len;
> +	vq->shadow_used_ring[vq->shadow_used_idx].id  = desc_chain_head;
> +	vq->shadow_used_ring[vq->shadow_used_idx].len = desc_chain_len;
> +	vq->shadow_used_idx++;
>  	vq->last_used_idx++;
> -	vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
> -				ring[used_idx]),
> -			sizeof(vq->used->ring[used_idx]));
> +}
> +
> +static inline void __attribute__((always_inline))
> +flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
> +		uint32_t used_idx_start)
> +{
> +	if (used_idx_start + vq->shadow_used_idx < vq->size) {
> +		rte_memcpy(&vq->used->ring[used_idx_start],
> +				&vq->shadow_used_ring[0],
> +				vq->shadow_used_idx *
> +				sizeof(struct vring_used_elem));
> +		vhost_log_used_vring(dev, vq,
> +				offsetof(struct vring_used,
> +					ring[used_idx_start]),
> +				vq->shadow_used_idx *
> +				sizeof(struct vring_used_elem));
> +	} else {
> +		uint32_t part_1 = vq->size - used_idx_start;
> +		uint32_t part_2 = vq->shadow_used_idx - part_1;
> +
> +		rte_memcpy(&vq->used->ring[used_idx_start],
> +				&vq->shadow_used_ring[0],
> +				part_1 *
> +				sizeof(struct vring_used_elem));
> +		vhost_log_used_vring(dev, vq,
> +				offsetof(struct vring_used,
> +					ring[used_idx_start]),
> +				part_1 *
> +				sizeof(struct vring_used_elem));
> +		rte_memcpy(&vq->used->ring[0],
> +				&vq->shadow_used_ring[part_1],
> +				part_2 *
> +				sizeof(struct vring_used_elem));
> +		vhost_log_used_vring(dev, vq,
> +				offsetof(struct vring_used,
> +					ring[0]),
> +				part_2 *
> +				sizeof(struct vring_used_elem));
> +	}
>  }
Is expanding the code done for performance purpose?
Or maybe we could have a loop to do that?
Something like this (not compiled, not tested):

static inline void __attribute__((always_inline))
flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
{
	uint32_t to = used_idx_start;
	uint32_t from = 0;
	uint32_t count;

	if (used_idx_start + vq->shadow_used_idx < vq->size)
		count = vq->shadow_used_idx;
	else
		count = vq->size - used_idx_start;

	do {
		rte_memcpy(&vq->used->ring[to],
				&vq->shadow_used_ring[from],
				count * sizeof(struct vring_used_elem));
		vhost_log_used_vring(dev, vq,
				offsetof(struct vring_used, ring[to]),
				count * sizeof(struct vring_used_elem));

		to = (to + count) & (vq->size - 1);
		from += count;
		count = vq->shadow_used_idx - count;
	} while (count);
}

Regards,
Maxime