Re: [RFC PATCH v5 11/26] vhost: Handle host notifiers in SVQ

[Jason Wang <jasowang@redhat.com>]

在 2021/10/30 上午2:35, Eugenio Pérez 写道:
> If device supports host notifiers, this makes one jump less (kernel) to
> deliver SVQ notifications to it.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.h |  2 ++
>   hw/virtio/vhost-shadow-virtqueue.c | 23 ++++++++++++++++++++++-
>   2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
> index 30ab9643b9..eb0a54f954 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -18,6 +18,8 @@ typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
>   void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
>   const EventNotifier *vhost_svq_get_dev_kick_notifier(
>                                                 const VhostShadowVirtqueue *svq);
> +void vhost_svq_set_host_mr_notifier(VhostShadowVirtqueue *svq, void *addr);
> +
>   void vhost_svq_start(struct vhost_dev *dev, unsigned idx,
>                        VhostShadowVirtqueue *svq, int svq_kick_fd);
>   void vhost_svq_stop(struct vhost_dev *dev, unsigned idx,
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index fda60d11db..e3dcc039b6 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -29,6 +29,12 @@ typedef struct VhostShadowVirtqueue {
>        * So shadow virtqueue must not clean it, or we would lose VirtQueue one.
>        */
>       EventNotifier svq_kick;
> +
> +    /* Device's host notifier memory region. NULL means no region */
> +    void *host_notifier_mr;
> +
> +    /* Virtio queue shadowing */
> +    VirtQueue *vq;
>   } VhostShadowVirtqueue;
>   
>   /**
> @@ -50,7 +56,20 @@ static void vhost_handle_guest_kick(EventNotifier *n)
>           return;
>       }
>   
> -    event_notifier_set(&svq->hdev_kick);
> +    if (svq->host_notifier_mr) {
> +        uint16_t *mr = svq->host_notifier_mr;
> +        *mr = virtio_get_queue_index(svq->vq);


Do we need barriers around the possible MMIO here?

To avoid those complicated stuff, I'd rather simply go with eventfd path.

Note mmio and eventfd are not mutually exclusive.

Thanks


> +    } else {
> +        event_notifier_set(&svq->hdev_kick);
> +    }
> +}
> +
> +/*
> + * Set the device's memory region notifier. addr = NULL clear it.
> + */
> +void vhost_svq_set_host_mr_notifier(VhostShadowVirtqueue *svq, void *addr)
> +{
> +    svq->host_notifier_mr = addr;
>   }
>   
>   /**
> @@ -134,6 +153,7 @@ void vhost_svq_stop(struct vhost_dev *dev, unsigned idx,
>    */
>   VhostShadowVirtqueue *vhost_svq_new(struct vhost_dev *dev, int idx)
>   {
> +    int vq_idx = dev->vq_index + idx;
>       g_autofree VhostShadowVirtqueue *svq = g_new0(VhostShadowVirtqueue, 1);
>       int r;
>   
> @@ -151,6 +171,7 @@ VhostShadowVirtqueue *vhost_svq_new(struct vhost_dev *dev, int idx)
>           goto err_init_hdev_call;
>       }
>   
> +    svq->vq = virtio_get_queue(dev->vdev, vq_idx);
>       return g_steal_pointer(&svq);
>   
>   err_init_hdev_call: