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virtio: event index support

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Add support for event_idx feature, and utilize it to
reduce the number of interrupts and exits for the guest.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2011-06-12 16:21:57 +03:00
parent 01731cfb39
commit bcbabae8ff
3 changed files with 97 additions and 10 deletions
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6
hw/vhost_net.c
View File

@ -50,6 +50,9 @@ unsigned vhost_net_get_features(struct vhost_net *net, unsigned features)
if (!(net->dev.features & (1 << VIRTIO_RING_F_INDIRECT_DESC))) {
features &= ~(1 << VIRTIO_RING_F_INDIRECT_DESC);
}
if (!(net->dev.features & (1 << VIRTIO_RING_F_EVENT_IDX))) {
features &= ~(1 << VIRTIO_RING_F_EVENT_IDX);
}
if (!(net->dev.features & (1 << VIRTIO_NET_F_MRG_RXBUF))) {
features &= ~(1 << VIRTIO_NET_F_MRG_RXBUF);
}
@ -65,6 +68,9 @@ 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_EVENT_IDX)) {
net->dev.acked_features |= (1 << VIRTIO_RING_F_EVENT_IDX);
}
if (features & (1 << VIRTIO_NET_F_MRG_RXBUF)) {
net->dev.acked_features |= (1 << VIRTIO_NET_F_MRG_RXBUF);
}

92
hw/virtio.c
View File

@ -71,7 +71,17 @@ struct VirtQueue
VRing vring;
target_phys_addr_t pa;
uint16_t last_avail_idx;
/* Last used index value we have signalled on */
uint16_t signalled_used;
/* Last used index value we have signalled on */
bool signalled_used_valid;
/* Notification enabled? */
bool notification;
int inuse;
uint16_t vector;
void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
VirtIODevice *vdev;
@ -140,6 +150,11 @@ static inline uint16_t vring_avail_ring(VirtQueue *vq, int i)
return lduw_phys(pa);
}
static inline uint16_t vring_used_event(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;
@ -161,11 +176,11 @@ static uint16_t vring_used_idx(VirtQueue *vq)
return lduw_phys(pa);
}
static inline void vring_used_idx_increment(VirtQueue *vq, uint16_t val)
static inline void vring_used_idx_set(VirtQueue *vq, uint16_t val)
{
target_phys_addr_t pa;
pa = vq->vring.used + offsetof(VRingUsed, idx);
stw_phys(pa, vring_used_idx(vq) + val);
stw_phys(pa, val);
}
static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
@ -182,12 +197,26 @@ static inline void vring_used_flags_unset_bit(VirtQueue *vq, int mask)
stw_phys(pa, lduw_phys(pa) & ~mask);
}
static inline void vring_avail_event(VirtQueue *vq, uint16_t val)
{
target_phys_addr_t pa;
if (!vq->notification) {
return;
}
pa = vq->vring.used + offsetof(VRingUsed, ring[vq->vring.num]);
stw_phys(pa, val);
}
void virtio_queue_set_notification(VirtQueue *vq, int enable)
{
if (enable)
vq->notification = enable;
if (vq->vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
vring_avail_event(vq, vring_avail_idx(vq));
} else if (enable) {
vring_used_flags_unset_bit(vq, VRING_USED_F_NO_NOTIFY);
else
} else {
vring_used_flags_set_bit(vq, VRING_USED_F_NO_NOTIFY);
}
}
int virtio_queue_ready(VirtQueue *vq)
@ -233,11 +262,16 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
void virtqueue_flush(VirtQueue *vq, unsigned int count)
{
uint16_t old, new;
/* Make sure buffer is written before we update index. */
wmb();
trace_virtqueue_flush(vq, count);
vring_used_idx_increment(vq, count);
old = vring_used_idx(vq);
new = old + count;
vring_used_idx_set(vq, new);
vq->inuse -= count;
if (unlikely((int16_t)(new - vq->signalled_used) < (uint16_t)(new - old)))
vq->signalled_used_valid = false;
}
void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
@ -394,6 +428,9 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem)
max = vq->vring.num;
i = head = virtqueue_get_head(vq, vq->last_avail_idx++);
if (vq->vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
vring_avail_event(vq, vring_avail_idx(vq));
}
if (vring_desc_flags(desc_pa, i) & VRING_DESC_F_INDIRECT) {
if (vring_desc_len(desc_pa, i) % sizeof(VRingDesc)) {
@ -477,6 +514,9 @@ void virtio_reset(void *opaque)
vdev->vq[i].last_avail_idx = 0;
vdev->vq[i].pa = 0;
vdev->vq[i].vector = VIRTIO_NO_VECTOR;
vdev->vq[i].signalled_used = 0;
vdev->vq[i].signalled_used_valid = false;
vdev->vq[i].notification = true;
}
}
@ -626,13 +666,45 @@ void virtio_irq(VirtQueue *vq)
virtio_notify_vector(vq->vdev, vq->vector);
}
/* Assuming a given event_idx value from the other size, if
* we have just incremented index from old to new_idx,
* should we trigger an event? */
static inline int vring_need_event(uint16_t event, uint16_t new, uint16_t old)
{
/* Note: Xen has similar logic for notification hold-off
* in include/xen/interface/io/ring.h with req_event and req_prod
* corresponding to event_idx + 1 and new respectively.
* Note also that req_event and req_prod in Xen start at 1,
* event indexes in virtio start at 0. */
return (uint16_t)(new - event - 1) < (uint16_t)(new - old);
}
static bool vring_notify(VirtIODevice *vdev, VirtQueue *vq)
{
uint16_t old, new;
bool v;
/* Always notify when queue is empty (when feature acknowledge) */
if (((vdev->guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY)) &&
!vq->inuse && vring_avail_idx(vq) == vq->last_avail_idx)) {
return true;
}
if (!(vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX))) {
return !(vring_avail_flags(vq) & VRING_AVAIL_F_NO_INTERRUPT);
}
v = vq->signalled_used_valid;
vq->signalled_used_valid = true;
old = vq->signalled_used;
new = vq->signalled_used = vring_used_idx(vq);
return !v || vring_need_event(vring_used_event(vq), new, old);
}
void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
{
/* 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)) ||
(vq->inuse || vring_avail_idx(vq) != vq->last_avail_idx)))
if (!vring_notify(vdev, vq)) {
return;
}
trace_virtio_notify(vdev, vq);
vdev->isr |= 0x01;
@ -715,6 +787,8 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f)
vdev->vq[i].vring.num = qemu_get_be32(f);
vdev->vq[i].pa = qemu_get_be64(f);
qemu_get_be16s(f, &vdev->vq[i].last_avail_idx);
vdev->vq[i].signalled_used_valid = false;
vdev->vq[i].notification = true;
if (vdev->vq[i].pa) {
uint16_t nheads;

9
hw/virtio.h
View File

@ -46,6 +46,11 @@
#define VIRTIO_F_NOTIFY_ON_EMPTY 24
/* We support indirect buffer descriptors */
#define VIRTIO_RING_F_INDIRECT_DESC 28
/* The Guest publishes the used index for which it expects an interrupt
* at the end of the avail ring. Host should ignore the avail->flags field. */
/* The Host publishes the avail index for which it expects a kick
* at the end of the used ring. Guest should ignore the used->flags field. */
#define VIRTIO_RING_F_EVENT_IDX 29
/* A guest should never accept this. It implies negotiation is broken. */
#define VIRTIO_F_BAD_FEATURE 30
@ -210,7 +215,9 @@ void virtio_serial_exit(VirtIODevice *vdev);
#define DEFINE_VIRTIO_COMMON_FEATURES(_state, _field) \
DEFINE_PROP_BIT("indirect_desc", _state, _field, \
VIRTIO_RING_F_INDIRECT_DESC, true)
VIRTIO_RING_F_INDIRECT_DESC, true), \
DEFINE_PROP_BIT("event_idx", _state, _field, \
VIRTIO_RING_F_EVENT_IDX, true)
target_phys_addr_t virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);