virtio: support unlocked queue kick
Based on patch by Christoph for virtio_blk speedup:
Split virtqueue_kick to be able to do the actual notification
outside the lock protecting the virtqueue. This patch was
originally done by Stefan Hajnoczi, but I can't find the
original one anymore and had to recreated it from memory.
Pointers to the original or corrections for the commit message
are welcome.
Stefan's patch was here:
https://github.com/stefanha/linux/commit/a6d06644e3a58e57a774e77d7dc34c4a5a2e7496
http://www.spinics.net/lists/linux-virtualization/msg14616.html
Third time's the charm!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 6ea92a6..c56bbe7 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -262,19 +262,22 @@
EXPORT_SYMBOL_GPL(virtqueue_add_buf);
/**
- * virtqueue_kick - update after add_buf
+ * virtqueue_kick_prepare - first half of split virtqueue_kick call.
* @vq: the struct virtqueue
*
- * After one or more virtqueue_add_buf calls, invoke this to kick
- * the other side.
+ * Instead of virtqueue_kick(), you can do:
+ * if (virtqueue_kick_prepare(vq))
+ * virtqueue_notify(vq);
*
- * Caller must ensure we don't call this with other virtqueue
- * operations at the same time (except where noted).
+ * This is sometimes useful because the virtqueue_kick_prepare() needs
+ * to be serialized, but the actual virtqueue_notify() call does not.
*/
-void virtqueue_kick(struct virtqueue *_vq)
+bool virtqueue_kick_prepare(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
u16 new, old;
+ bool needs_kick;
+
START_USE(vq);
/* Descriptors and available array need to be set before we expose the
* new available array entries. */
@@ -287,13 +290,46 @@
/* Need to update avail index before checking if we should notify */
virtio_mb(vq);
- if (vq->event ?
- vring_need_event(vring_avail_event(&vq->vring), new, old) :
- !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
- /* Prod other side to tell it about changes. */
- vq->notify(&vq->vq);
-
+ if (vq->event) {
+ needs_kick = vring_need_event(vring_avail_event(&vq->vring),
+ new, old);
+ } else {
+ needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
+ }
END_USE(vq);
+ return needs_kick;
+}
+EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
+
+/**
+ * virtqueue_notify - second half of split virtqueue_kick call.
+ * @vq: the struct virtqueue
+ *
+ * This does not need to be serialized.
+ */
+void virtqueue_notify(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+
+ /* Prod other side to tell it about changes. */
+ vq->notify(_vq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_notify);
+
+/**
+ * virtqueue_kick - update after add_buf
+ * @vq: the struct virtqueue
+ *
+ * After one or more virtqueue_add_buf calls, invoke this to kick
+ * the other side.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
+void virtqueue_kick(struct virtqueue *vq)
+{
+ if (virtqueue_kick_prepare(vq))
+ virtqueue_notify(vq);
}
EXPORT_SYMBOL_GPL(virtqueue_kick);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index ec1706e..31fe3a6 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -34,6 +34,10 @@
void virtqueue_kick(struct virtqueue *vq);
+bool virtqueue_kick_prepare(struct virtqueue *vq);
+
+void virtqueue_notify(struct virtqueue *vq);
+
void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
void virtqueue_disable_cb(struct virtqueue *vq);