Re: [dpdk-dev] [PATCH v5 09/15] vhost: add shadow used ring support for packed rings

[Tiwei Bie <tiwei.bie@intel.com>]

On Fri, Jun 22, 2018 at 03:43:21PM +0200, Maxime Coquelin wrote:
[...]
> index 671b4b3bf..62d49f238 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -80,6 +80,12 @@ struct log_cache_entry {
>  	unsigned long val;
>  };
>  
> +struct vring_used_elem_packed {
> +	uint32_t id;

Id in packed ring is 16 bits long. Maybe it's better
to define it as uint16_t here.

> +	uint32_t len;
> +	uint32_t count;
> +};
> +
[...]
> +
> +static __rte_always_inline void
> +flush_shadow_used_ring_packed(struct virtio_net *dev,
> +			struct vhost_virtqueue *vq)
> +{
> +	int i;
> +	uint16_t used_idx = vq->last_used_idx;
> +
> +	/* Split loop in two to save memory barriers */
> +	for (i = 0; i < vq->shadow_used_idx; i++) {
> +		vq->desc_packed[used_idx].index = vq->shadow_used_packed[i].id;
> +		vq->desc_packed[used_idx].len = vq->shadow_used_packed[i].len;
> +
> +		used_idx += vq->shadow_used_packed[i].count;

used_idx may wrap.

> +	}
> +
> +	rte_smp_wmb();
> +
> +	for (i = 0; i < vq->shadow_used_idx; i++) {
> +		uint16_t flags;
> +
> +		if (vq->shadow_used_packed[i].len)
> +			flags = VRING_DESC_F_WRITE;
> +		else
> +			flags = 0;
> +
> +		if (vq->used_wrap_counter) {
> +			flags |= VRING_DESC_F_USED;
> +			flags |= VRING_DESC_F_AVAIL;
> +		} else {
> +			flags &= ~VRING_DESC_F_USED;
> +			flags &= ~VRING_DESC_F_AVAIL;
> +		}
> +
> +		vq->desc_packed[vq->last_used_idx].flags = flags;
> +
> +		vhost_log_cache_used_vring(dev, vq,
> +					vq->last_used_idx *
> +					sizeof(struct vring_desc_packed),
> +					sizeof(struct vring_desc_packed));
> +
> +		vq->last_used_idx += vq->shadow_used_packed[i].count;
> +		if (vq->last_used_idx >= vq->size) {
> +			vq->used_wrap_counter ^= 1;
> +			vq->last_used_idx -= vq->size;
> +		}
> +	}
> +
> +	rte_smp_wmb();
> +	vq->shadow_used_idx = 0;
> +	vhost_log_cache_sync(dev, vq);
> +}
> +
> +static __rte_always_inline void
> +update_shadow_used_ring_packed(struct vhost_virtqueue *vq,
> +			 uint16_t desc_idx, uint16_t len, uint16_t count)
> +{
> +	uint16_t i = vq->shadow_used_idx++;
> +
> +	vq->shadow_used_packed[i].id  = desc_idx;
> +	vq->shadow_used_packed[i].len = len;
> +	vq->shadow_used_packed[i].count = count;
>  }
>  
>  static inline void
> -- 
> 2.14.4
>