From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: [PATCH] virtio: don't always force a notification when ring is full Date: Thu, 19 Jun 2008 09:40:56 +1000 Message-ID: <200806190940.57083.rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: virtualization@lists.linux-foundation.org Cc: Christian Borntraeger , Anthony Liguori List-Id: virtualization@lists.linuxfoundation.org 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. It even makes a difference with lguest's crappy network implementation: 1GB guest->host before: 30.0844 1GB guest->host after: 27.6167 Signed-off-by: Rusty Russell diff -r 89bf4894cc36 drivers/virtio/virtio_ring.c --- a/drivers/virtio/virtio_ring.c Mon Jun 16 14:31:30 2008 +1000 +++ b/drivers/virtio/virtio_ring.c Wed Jun 18 16:15:49 2008 +1000 @@ -87,8 +87,11 @@ static int vring_add_buf(struct virtqueu 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); END_USE(vq); return -ENOSPC; }