Re: [dpdk-dev] [PATCH] vhost: fix vhost interrupt support

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Tiwei,

On 09/05/2018 01:55 AM, Tiwei Bie wrote:
> When VIRTIO_RING_F_EVENT_IDX is negotiated, we need to
> update the avail event to enable the notification.
> 
> Fixes: 3f8ff12821e4 ("vhost: support interrupt mode")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
>   lib/librte_vhost/Makefile |  1 +
>   lib/librte_vhost/vhost.c  | 18 ++++++++++++------
>   lib/librte_vhost/vhost.h  |  2 ++
>   3 files changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> index de431fbb7..531cf4832 100644
> --- a/lib/librte_vhost/Makefile
> +++ b/lib/librte_vhost/Makefile
> @@ -13,6 +13,7 @@ LIBABIVER := 4
>   CFLAGS += -DALLOW_EXPERIMENTAL_API
>   CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3 -D_FILE_OFFSET_BITS=64
>   CFLAGS += -I vhost_user
> +CFLAGS += -fno-strict-aliasing

I'm not clear why this is needed looking at the code below,
could you please explain?

>   LDLIBS += -lpthread
>   
>   ifeq ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 3c9be10a0..88b1781d5 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -646,12 +646,18 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
>   }
>   
>   static inline void
> -vhost_enable_notify_split(struct vhost_virtqueue *vq, int enable)
> +vhost_enable_notify_split(struct virtio_net *dev,
> +		struct vhost_virtqueue *vq, int enable)
>   {
> -	if (enable)
> -		vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> -	else
> -		vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> +	if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
> +		if (enable)
> +			vq->used->flags &= ~VRING_USED_F_NO_NOTIFY;
> +		else
> +			vq->used->flags |= VRING_USED_F_NO_NOTIFY;
> +	} else {
> +		if (enable)
> +			vhost_avail_event(vq) = vq->last_avail_idx;
> +	}
>   }
>   
>   static inline void
> @@ -689,7 +695,7 @@ rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int enable)
>   	if (vq_is_packed(dev))
>   		vhost_enable_notify_packed(dev, vq, enable);
>   	else
> -		vhost_enable_notify_split(vq, enable);
> +		vhost_enable_notify_split(dev, vq, enable);
>   
>   	return 0;
>   }
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 760a09c0d..25ffd7614 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -648,6 +648,8 @@ vhost_iova_to_vva(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	return __vhost_iova_to_vva(dev, vq, iova, len, perm);
>   }
>   
> +#define vhost_avail_event(vr) \
> +	(*(volatile uint16_t*)&(vr)->used->ring[(vr)->size])
>   #define vhost_used_event(vr) \
>   	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
>   
>