Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH 09/18] virtio: use avail_event index | Date | Mon, 09 May 2011 14:03:26 +0930 |
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On Wed, 4 May 2011 23:51:47 +0300, "Michael S. Tsirkin" <mst@redhat.com> wrote: > Use the new avail_event feature to reduce the number > of exits from the guest.
Figures here would be nice :)
> @@ -228,6 +237,12 @@ add_head: > * new available array entries. */ > virtio_wmb(); > vq->vring.avail->idx++; > + /* If the driver never bothers to kick in a very long while, > + * avail index might wrap around. If that happens, invalidate > + * kicked_avail index we stored. TODO: make sure all drivers > + * kick at least once in 2^16 and remove this. */ > + if (unlikely(vq->vring.avail->idx == vq->kicked_avail)) > + vq->kicked_avail_valid = true;
If they don't, they're already buggy. Simply do: WARN_ON(vq->vring.avail->idx == vq->kicked_avail);
> +static bool vring_notify(struct vring_virtqueue *vq) > +{ > + u16 old, new; > + bool v; > + if (!vq->event) > + return !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY); > + > + v = vq->kicked_avail_valid; > + old = vq->kicked_avail; > + new = vq->kicked_avail = vq->vring.avail->idx; > + vq->kicked_avail_valid = true; > + if (unlikely(!v)) > + return true;
This is the only place you actually used kicked_avail_valid. Is it possible to initialize it in such a way that you can remove this?
> @@ -482,6 +517,8 @@ void vring_transport_features(struct virtio_device *vdev) > break; > case VIRTIO_RING_F_USED_EVENT_IDX: > break; > + case VIRTIO_RING_F_AVAIL_EVENT_IDX: > + break; > default: > /* We don't understand this bit. */ > clear_bit(i, vdev->features);
Does this belong in a prior patch?
Thanks, Rusty.
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