[dpdk-dev] [PATCH v7 14/15] vhost: add notification for packed ring

[Maxime Coquelin]

On 07/05/2018 07:12 AM, Tiwei Bie wrote:
> 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.
> 

I will align on Kernel header.

>>   #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?

Yes, thanks for pointing this out.

So if not valid, I'll kick if desc_event_flags != VRING_EVENT_F_DISABLE.

>> +	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?

Right, I'll fix it in next version.

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