From 86f990ba73c75413f4359d43349e8979b935059b Mon Sep 17 00:00:00 2001
From: Michael S. Tsirkin <mst@redhat.com>
Date: Mon, 24 May 2010 09:59:17 -0300
Subject: [PATCH 2/2] virtio: utilize PUBLISH_USED_IDX feature
RH-Author: Michael S. Tsirkin <mst@redhat.com>
Message-id: <20100524095917.GA28246@redhat.com>
Patchwork-id: 9484
O-Subject: [PATCH] virtio: utilize PUBLISH_USED_IDX feature
Bugzilla: 595287
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Avi Kivity <avi@redhat.com>
RH-Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reduces irq_window in guest by only injecting
an interrupt if guest has handled all buffers we
used so far.
Feature only added to virtio-net so far, as
benefit for block was not yet shown.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This is the userspace part of the virtio changes.
Upstream status: posted, upstream will need another change for layout
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=595287
---
hw/vhost_net.c | 3 +++
hw/virtio-net.h | 2 ++
hw/virtio.c | 15 +++++++++++++++
hw/virtio.h | 2 ++
4 files changed, 22 insertions(+), 0 deletions(-)
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
hw/vhost_net.c | 3 +++
hw/virtio-net.h | 2 ++
hw/virtio.c | 15 +++++++++++++++
hw/virtio.h | 2 ++
4 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/hw/vhost_net.c b/hw/vhost_net.c
index 7d81cac..a2ff80b 100644
--- a/hw/vhost_net.c
+++ b/hw/vhost_net.c
@@ -65,6 +65,9 @@ void vhost_net_ack_features(struct vhost_net *net, unsigned features)
if (features & (1 << VIRTIO_RING_F_INDIRECT_DESC)) {
net->dev.acked_features |= (1 << VIRTIO_RING_F_INDIRECT_DESC);
}
+ if (features & (1 << VIRTIO_RING_F_PUBLISH_USED)) {
+ net->dev.acked_features |= (1 << VIRTIO_RING_F_PUBLISH_USED);
+ }
}
static int vhost_net_get_fd(VLANClientState *backend)
diff --git a/hw/virtio-net.h b/hw/virtio-net.h
index e55119b..27c63ee 100644
--- a/hw/virtio-net.h
+++ b/hw/virtio-net.h
@@ -155,6 +155,8 @@ struct virtio_net_ctrl_mac {
#define DEFINE_VIRTIO_NET_FEATURES(_state, _field) \
DEFINE_VIRTIO_COMMON_FEATURES(_state, _field), \
+ DEFINE_PROP_BIT("publish_used", _state, _field, \
+ VIRTIO_RING_F_PUBLISH_USED, true), \
DEFINE_PROP_BIT("csum", _state, _field, VIRTIO_NET_F_CSUM, true), \
DEFINE_PROP_BIT("guest_csum", _state, _field, VIRTIO_NET_F_GUEST_CSUM, true), \
DEFINE_PROP_BIT("gso", _state, _field, VIRTIO_NET_F_GSO, true), \
diff --git a/hw/virtio.c b/hw/virtio.c
index e7657ae..3e09acd 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -71,6 +71,7 @@ struct VirtQueue
target_phys_addr_t pa;
uint16_t last_avail_idx;
int inuse;
+ int num_notify;
uint16_t vector;
void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
VirtIODevice *vdev;
@@ -139,6 +140,11 @@ static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
return lduw_phys(pa);
}
+static inline uint16_t vring_last_used_idx(VirtQueue *vq)
+{
+ return vring_avail_ring(vq, vq->vring.num);
+}
+
static inline void vring_used_ring_id(VirtQueue *vq, int i, uint32_t val)
{
target_phys_addr_t pa;
@@ -234,6 +240,7 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
wmb();
vring_used_idx_increment(vq, count);
vq->inuse -= count;
+ vq->num_notify += count;
}
void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
@@ -603,6 +610,14 @@ void virtio_irq(VirtQueue *vq)
void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
{
+ uint16_t n = vq->num_notify;
+ vq->num_notify = 0;
+
+ /* Do not notify if guest did not yet see the last update. */
+ if ((vdev->guest_features & (1 << VIRTIO_RING_F_PUBLISH_USED)) &&
+ (uint16_t)(vring_last_used_idx(vq) - vring_used_idx(vq) + n) >= n)
+ return;
+
/* Always notify when queue is empty (when feature acknowledge) */
if ((vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT) &&
(!(vdev->guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) ||
diff --git a/hw/virtio.h b/hw/virtio.h
index f885f1b..8bd75f9 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -43,6 +43,8 @@
#define VIRTIO_F_NOTIFY_ON_EMPTY 24
/* We support indirect buffer descriptors */
#define VIRTIO_RING_F_INDIRECT_DESC 28
+/* The Guest publishes last-seen used index at the end of the avail ring. */
+#define VIRTIO_RING_F_PUBLISH_USED 29
/* A guest should never accept this. It implies negotiation is broken. */
#define VIRTIO_F_BAD_FEATURE 30
--
1.7.0.3