diff options
authorRusty Russell <rusty@rustcorp.com.au>2008-07-25 12:06:04 -0500
committerRusty Russell <rusty@rustcorp.com.au>2008-07-25 12:06:04 +1000
commit44653eae1407f79dff6f52fcf594ae84cb165ec4 (patch)
parent674bfc23c585b34c42263d73fb51710d49762a23 (diff)
virtio: don't always force a notification when ring is full
We force notification when the ring is full, even if the host has indicated it doesn't want to know. This seemed like a good idea at the time: if we fill the transmit ring, we should tell the host immediately. Unfortunately this logic also applies to the receiving ring, which is refilled constantly. We should introduce real notification thesholds to replace this logic. Meanwhile, removing the logic altogether breaks the heuristics which KVM uses, so we use a hack: only notify if there are outgoing parts of the new buffer. Here are the number of exits with lguest's crappy network implementation: Before: network xmit 7859051 recv 236420 After: network xmit 7858610 recv 118136 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
1 files changed, 5 insertions, 2 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 72bf8bc0901..21d9a62767a 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -87,8 +87,11 @@ static int vring_add_buf(struct virtqueue *_vq,
if (vq->num_free < out + in) {
pr_debug("Can't add buf len %i - avail = %i\n",
out + in, vq->num_free);
- /* We notify *even if* VRING_USED_F_NO_NOTIFY is set here. */
- vq->notify(&vq->vq);
+ /* FIXME: for historical reasons, we force a notify here if
+ * there are outgoing parts to the buffer. Presumably the
+ * host should service the ring ASAP. */
+ if (out)
+ vq->notify(&vq->vq);
return -ENOSPC;