Re: [RFC v2 13/13] vhost: Use VRING_AVAIL_F_NO_INTERRUPT at device call on shadow virtqueue

[Jason Wang]

在 2021/3/16 上午3:48, Eugenio Pérez 写道:
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.c | 28 +++++++++++++++++++++++++++-
>   1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index 7df98fc43f..e3879a4622 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -71,10 +71,35 @@ typedef struct VhostShadowVirtqueue {
>       /* Next head to consume from device */
>       uint16_t used_idx;
>   
> +    /* Cache for the exposed notification flag */
> +    bool notification;
> +
>       /* Descriptors copied from guest */
>       vring_desc_t descs[];
>   } VhostShadowVirtqueue;
>   
> +static void vhost_shadow_vq_set_notification(VhostShadowVirtqueue *svq,
> +                                             bool enable)
> +{
> +    uint16_t notification_flag;
> +
> +    if (svq->notification == enable) {
> +        return;
> +    }
> +
> +    notification_flag = virtio_tswap16(svq->vdev, VRING_AVAIL_F_NO_INTERRUPT);
> +
> +    svq->notification = enable;
> +    if (enable) {
> +        svq->vring.avail->flags &= ~notification_flag;
> +    } else {
> +        svq->vring.avail->flags |= notification_flag;
> +    }
> +
> +    /* Make sure device reads our flag */
> +    smp_mb();


This is a hint, so we don't need memory barrier here.

Thanks


> +}
> +
>   static void vhost_vring_write_descs(VhostShadowVirtqueue *svq,
>                                       const struct iovec *iovec,
>                                       size_t num, bool more_descs, bool write)
> @@ -251,7 +276,7 @@ static void 
> vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
>       do {
>           unsigned i = 0;
>   
> -        /* TODO: Use VRING_AVAIL_F_NO_INTERRUPT */
> +        vhost_shadow_vq_set_notification(svq, false);
>           while (true) {
>               g_autofree VirtQueueElement *elem = vhost_shadow_vq_get_buf(svq);
>               if (!elem) {
> @@ -269,6 +294,7 @@ static void 
> vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
>               svq->masked_notifier.signaled = true;
>               event_notifier_set(svq->masked_notifier.n);
>           }
> +        vhost_shadow_vq_set_notification(svq, true);
>       } while (vhost_shadow_vq_more_used(svq));
>   
>       if (masked_notifier) {