Re: [PATCH v7 14/15] vhost: add notification for packed ring

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

On Wed, Jul 04, 2018 at 11:54:37PM +0200, Maxime Coquelin wrote:
[...]
> @@ -225,6 +231,15 @@ struct vring_desc_packed {
>  	uint16_t index;
>  	uint16_t flags;
>  };
> +
> +#define VRING_EVENT_F_ENABLE 0x0
> +#define VRING_EVENT_F_DISABLE 0x1
> +#define VRING_EVENT_F_DESC 0x2
> +
> +struct vring_packed_desc_event {
> +	uint16_t desc_event_off_wrap;
> +	uint16_t desc_event_flags;
> +};

As all above types (including struct vring_desc_packed)
and macros are being protected by VIRTIO_F_RING_PACKED,
and they won't be defined if VIRTIO_F_RING_PACKED is
defined in kernel header. We may want to unify the names.

For the types, we may have below types defined in
linux uapi:

struct vring_packed;
struct vring_packed_desc;
struct vring_packed_desc_event;

They can also be named as:

struct vring_packed;
struct vring_desc_packed;
struct vring_packed_desc_event;

We need to choose one of them or something else.

For the `struct vring_packed_desc_event`, it can
be defined as:

struct vring_packed_desc_event {
	uint16_t off_wrap;
	uint16_t flags;
};

or

struct vring_packed_desc_event {
	uint16_t desc_event_off_wrap;
	uint16_t desc_event_flags;
};

We need to choose one of them or something else.

For the `struct vring_packed_desc`, it can be
defined as:

struct vring_packed_desc {
	uint64_t addr;
	uint32_t len;
	uint16_t index;
	uint16_t flags;
};

or

struct vring_packed_desc {
	uint64_t addr;
	uint32_t len;
	uint16_t id;		// index -> id
	uint16_t flags;
};

We need to choose one of them or something else.


>  #endif
>  
[...]
> +static __rte_always_inline void
> +vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
> +{
> +	uint16_t old, new, off, off_wrap;
> +	bool kick = false;
> +
> +	/* Flush used desc update. */
> +	rte_smp_mb();
> +
> +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
> +		if (vq->driver_event->desc_event_flags !=
> +				VRING_EVENT_F_DISABLE)
> +			kick = true;
> +		goto kick;
> +	}
> +
> +	old = vq->signalled_used;

We also need to check whether vq->signalled_used is valid?

> +	new = vq->last_used_idx;
> +	vq->signalled_used = new;
> +
> +	if (vq->driver_event->desc_event_flags != VRING_EVENT_F_DESC) {
> +		if (vq->driver_event->desc_event_flags !=
> +				VRING_EVENT_F_DISABLE)
> +			kick = true;
> +		goto kick;
> +	}
> +
> +	rte_smp_rmb();
> +
> +	off_wrap = vq->driver_event->desc_event_off_wrap;
> +	off = off_wrap & ~(1 << 15);
> +
> +	if (vq->used_wrap_counter != off_wrap >> 15)
> +		off -= vq->size;
> +
> +	if (vhost_need_event(off, new, old))
> +		kick = true;

If new <= old, old needs to -= vq->size?

> +kick:
> +	if (kick)
> +		eventfd_write(vq->callfd, (eventfd_t)1);
> +}
> +
[...]