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authorMichael S. Tsirkin <mst@redhat.com>2011-05-20 02:11:14 +0300
committerRusty Russell <rusty@rustcorp.com.au>2011-05-30 11:14:16 +0930
commit7ab358c23cbf15cea08129cd722d1ce77433a94d (patch)
tree713d38823efda30222230314bcae26b919782f16 /drivers/virtio
parent4423fe40b03f32b11e72ecfa03077e702e55d5a9 (diff)
virtio: add api for delayed callbacks
Add an API that tells the other side that callbacks should be delayed until a lot of work has been done. Implement using the new event_idx feature. Note: it might seem advantageous to let the drivers ask for a callback after a specific capacity has been reached. However, as a single head can free many entries in the descriptor table, we don't really have a clue about capacity until get_buf is called. The API is the simplest to implement at the moment, we'll see what kind of hints drivers can pass when there's more than one user of the feature. Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c27
1 files changed, 27 insertions, 0 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a5fadc40c44..68b9136847a 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -376,6 +376,33 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
+bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ u16 bufs;
+
+ START_USE(vq);
+
+ /* We optimistically turn back on interrupts, then check if there was
+ * more to do. */
+ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
+ * either clear the flags bit or point the event index at the next
+ * entry. Always do both to keep code simple. */
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ /* TODO: tune this threshold */
+ bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
+ vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
+ virtio_mb();
+ if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
+ END_USE(vq);
+ return false;
+ }
+
+ END_USE(vq);
+ return true;
+}
+EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
+
void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);