Re: [PATCH 09/18] virtio: use avail_event index
From: Rusty Russell <hidden>
Date: 2011-05-09 04:33:26
Possibly related (same subject, not in this thread)
- 2011-05-19 · Re: [PATCH 09/18] virtio: use avail_event index · "Michael S. Tsirkin" <mst@redhat.com>
- 2011-05-18 · Re: [PATCH 09/18] virtio: use avail_event index · "Michael S. Tsirkin" <mst@redhat.com>
- 2011-05-18 · Re: [PATCH 09/18] virtio: use avail_event index · Rusty Russell <hidden>
- 2011-05-17 · Re: [PATCH 09/18] virtio: use avail_event index · Tom Lendacky <hidden>
- 2011-05-17 · Re: [PATCH 09/18] virtio: use avail_event index · "Michael S. Tsirkin" <mst@redhat.com>
On Wed, 4 May 2011 23:51:47 +0300, "Michael S. Tsirkin" [off-list ref] wrote:
Use the new avail_event feature to reduce the number of exits from the guest.
Figures here would be nice :)
quoted hunk ↗ jump to hunk
@@ -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?
quoted hunk ↗ jump to hunk
@@ -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.