From: Wei Xu <w...@redhat.com>
Difference between 'avail_wrap_counter' and 'last_avail_wrap_counter':
For Tx(guest transmitting), they are the same after each pop of a desc.
For Rx(guest receiving), they are also the same when there are enough
descriptors to carry the payload for a packet(e.g. usually 16 descs are
needed for a 64k packet in typical iperf tcp connection with tso enabled),
however, when the ring is running out of descriptors while there are
still a few free ones, e.g. 6 descriptors are available which is not
enough to carry an entire packet which needs 16 descriptors, in this
case the 'avail_wrap_counter' should be set as the first one pending
being handled by guest driver in order to get a notification, and the
'last_avail_wrap_counter' should stay unchanged to the head of available
descriptors, like below:
Mark meaning:
| | -- available
|*| -- used
A Snapshot of the queue:
last_avail_idx = 253
last_avail_wrap_counter = 1
|
+---------------------------------------------+
0 | | | |*|*|*|*|*|*|*|*|*|*|*|*|*|*|*|*|*| | | | 255
+---------------------------------------------+
|
shadow_avail_idx = 3
avail_wrap_counter = 0
Signed-off-by: Wei Xu <w...@redhat.com>
---
hw/virtio/virtio.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 128 insertions(+), 9 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 7e276b4..8cfc7b6 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -234,6 +234,34 @@ static void vring_desc_read(VirtIODevice *vdev, VRingDesc
*desc,
virtio_tswap16s(vdev, &desc->next);
}
+static void vring_packed_event_read(VirtIODevice *vdev,
+ MemoryRegionCache *cache, VRingPackedDescEvent *e)
+{
+ address_space_read_cached(cache, 0, e, sizeof(*e));
+ virtio_tswap16s(vdev, &e->off_wrap);
+ virtio_tswap16s(vdev, &e->flags);
+}
+
+static void vring_packed_off_wrap_write(VirtIODevice *vdev,
+ MemoryRegionCache *cache, uint16_t off_wrap)
+{
+ virtio_tswap16s(vdev, &off_wrap);
+ address_space_write_cached(cache, offsetof(VRingPackedDescEvent, off_wrap),
+ &off_wrap, sizeof(off_wrap));
+ address_space_cache_invalidate(cache,
+ offsetof(VRingPackedDescEvent, off_wrap), sizeof(off_wrap));
+}
+
+static void vring_packed_flags_write(VirtIODevice *vdev,
+ MemoryRegionCache *cache, uint16_t flags)
+{
+ virtio_tswap16s(vdev, &flags);
+ address_space_write_cached(cache, offsetof(VRingPackedDescEvent, flags),
+ &flags, sizeof(flags));
+ address_space_cache_invalidate(cache,
+ offsetof(VRingPackedDescEvent, flags), sizeof(flags));
+}
+
static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
{
VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
@@ -340,14 +368,8 @@ static inline void vring_set_avail_event(VirtQueue *vq,
uint16_t val)
address_space_cache_invalidate(&caches->used, pa, sizeof(val));
}
-void virtio_queue_set_notification(VirtQueue *vq, int enable)
+static void virtio_queue_set_notification_split(VirtQueue *vq, int enable)
{
- vq->notification = enable;
-
- if (!vq->vring.desc) {
- return;
- }
-
rcu_read_lock();
if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
vring_set_avail_event(vq, vring_avail_idx(vq));
@@ -363,6 +385,57 @@ void virtio_queue_set_notification(VirtQueue *vq, int
enable)
rcu_read_unlock();
}
+static void virtio_queue_set_notification_packed(VirtQueue *vq, int enable)
+{
+ VRingPackedDescEvent e;
+ VRingMemoryRegionCaches *caches;
+
+ rcu_read_lock();
+ caches = vring_get_region_caches(vq);
+ vring_packed_event_read(vq->vdev, &caches->used, &e);
+
+ if (!enable) {
+ if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+ /* no need to write device area since this is outdated. */
+ goto out;
+ }
+
+ e.flags = VRING_PACKED_EVENT_FLAG_DISABLE;
+ goto update;
+ }
+
+ e.flags = VRING_PACKED_EVENT_FLAG_ENABLE;
+ if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+ uint16_t off_wrap = vq->shadow_avail_idx | vq->avail_wrap_counter <<
15;
+
+ vring_packed_off_wrap_write(vq->vdev, &caches->used, off_wrap);
+ /* Make sure off_wrap is wrote before flags */
+ smp_wmb();
+
+ e.flags = VRING_PACKED_EVENT_FLAG_DESC;
+ }
+
+update:
+ vring_packed_flags_write(vq->vdev, &caches->used, e.flags);
+out:
+ rcu_read_unlock();
+}
+
+void virtio_queue_set_notification(VirtQueue *vq, int enable)
+{
+ vq->notification = enable;
+
+ if (!vq->vring.desc) {
+ return;
+ }
+
+ if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+ virtio_queue_set_notification_packed(vq, enable);
+ } else {
+ virtio_queue_set_notification_split(vq, enable);
+ }
+}
+
int virtio_queue_ready(VirtQueue *vq)
{
return vq->vring.avail != 0;
@@ -2117,8 +2190,7 @@ static void virtio_set_isr(VirtIODevice *vdev, int value)
}
}
-/* Called within rcu_read_lock(). */
-static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
{
uint16_t old, new;
bool v;
@@ -2141,6 +2213,53 @@ static bool virtio_should_notify(VirtIODevice *vdev,
VirtQueue *vq)
return !v || vring_need_event(vring_get_used_event(vq), new, old);
}
+static bool vring_packed_need_event(VirtQueue *vq, bool wrap,
+ uint16_t off_wrap, uint16_t new, uint16_t old)
+{
+ int off = off_wrap & ~(1 << 15);
+
+ if (wrap != off_wrap >> 15) {
+ off -= vq->vring.num;
+ }
+
+ return vring_need_event(off, new, old);
+}
+
+static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+ VRingPackedDescEvent e;
+ uint16_t old, new;
+ bool v;
+ VRingMemoryRegionCaches *caches;
+
+ caches = vring_get_region_caches(vq);
+ vring_packed_event_read(vdev, &caches->avail, &e);
+
+ old = vq->signalled_used;
+ new = vq->signalled_used = vq->used_idx;
+ v = vq->signalled_used_valid;
+ vq->signalled_used_valid = true;
+
+ if (e.flags == VRING_PACKED_EVENT_FLAG_DISABLE) {
+ return false;
+ } else if (e.flags == VRING_PACKED_EVENT_FLAG_ENABLE) {
+ return true;
+ }
+
+ return !v || vring_packed_need_event(vq,
+ vq->used_wrap_counter, e.off_wrap, new, old);
+}
+
+/* Called within rcu_read_lock(). */
+static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+ if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
+ return virtio_packed_should_notify(vdev, vq);
+ } else {
+ return virtio_split_should_notify(vdev, vq);
+ }
+}
+
void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
{
bool should_notify;
--
1.8.3.1
