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virtio: backend virtqueue notifier masking

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some backends (notably vhost) can mask events
at their source in a way that is more efficient
than masking through kvm.
Specifically
- masking in kvm uses rcu write side so it has high latency
- in kvm on unmask we always send an interrupt
masking at source does not have these issues.

Add such support in virtio.h and use in virtio-pci.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin 2012-12-24 17:35:27 +02:00
parent 774345f981
commit f1d0f15a6d
2 changed files with 83 additions and 9 deletions
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79
hw/virtio-pci.c
View file

@ -510,6 +510,31 @@ static void kvm_virtio_pci_vq_vector_release(VirtIOPCIProxy *proxy,
}
}
static int kvm_virtio_pci_irqfd_use(VirtIOPCIProxy *proxy,
unsigned int queue_no,
unsigned int vector)
{
VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];
VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);
EventNotifier *n = virtio_queue_get_guest_notifier(vq);
int ret;
ret = kvm_irqchip_add_irqfd_notifier(kvm_state, n, irqfd->virq);
return ret;
}
static void kvm_virtio_pci_irqfd_release(VirtIOPCIProxy *proxy,
unsigned int queue_no,
unsigned int vector)
{
VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);
EventNotifier *n = virtio_queue_get_guest_notifier(vq);
VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];
int ret;
ret = kvm_irqchip_remove_irqfd_notifier(kvm_state, n, irqfd->virq);
assert(ret == 0);
}
static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, int nvqs)
{
PCIDevice *dev = &proxy->pci_dev;
@ -531,6 +556,16 @@ static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, int nvqs)
if (ret < 0) {
goto undo;
}
/* If guest supports masking, set up irqfd now.
* Otherwise, delay until unmasked in the frontend.
*/
if (proxy->vdev->guest_notifier_mask) {
ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
if (ret < 0) {
kvm_virtio_pci_vq_vector_release(proxy, vector);
goto undo;
}
}
}
return 0;
@ -540,6 +575,9 @@ undo:
if (vector >= msix_nr_vectors_allocated(dev)) {
continue;
}
if (proxy->vdev->guest_notifier_mask) {
kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);
}
kvm_virtio_pci_vq_vector_release(proxy, vector);
}
return ret;
@ -560,6 +598,12 @@ static void kvm_virtio_pci_vector_release(VirtIOPCIProxy *proxy, int nvqs)
if (vector >= msix_nr_vectors_allocated(dev)) {
continue;
}
/* If guest supports masking, clean up irqfd now.
* Otherwise, it was cleaned when masked in the frontend.
*/
if (proxy->vdev->guest_notifier_mask) {
kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);
}
kvm_virtio_pci_vq_vector_release(proxy, vector);
}
}
@ -581,7 +625,19 @@ static int kvm_virtio_pci_vq_vector_unmask(VirtIOPCIProxy *proxy,
}
}
ret = kvm_irqchip_add_irqfd_notifier(kvm_state, n, irqfd->virq);
/* If guest supports masking, irqfd is already setup, unmask it.
* Otherwise, set it up now.
*/
if (proxy->vdev->guest_notifier_mask) {
proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, false);
/* Test after unmasking to avoid losing events. */
if (proxy->vdev->guest_notifier_pending &&
proxy->vdev->guest_notifier_pending(proxy->vdev, queue_no)) {
event_notifier_set(n);
}
} else {
ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
}
return ret;
}
@ -589,13 +645,14 @@ static void kvm_virtio_pci_vq_vector_mask(VirtIOPCIProxy *proxy,
unsigned int queue_no,
unsigned int vector)
{
VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);
EventNotifier *n = virtio_queue_get_guest_notifier(vq);
VirtIOIRQFD *irqfd = &proxy->vector_irqfd[vector];
int ret;
ret = kvm_irqchip_remove_irqfd_notifier(kvm_state, n, irqfd->virq);
assert(ret == 0);
/* If guest supports masking, keep irqfd but mask it.
* Otherwise, clean it up now.
*/
if (proxy->vdev->guest_notifier_mask) {
proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, true);
} else {
kvm_virtio_pci_irqfd_release(proxy, vector, queue_no);
}
}
static int kvm_virtio_pci_vector_unmask(PCIDevice *dev, unsigned vector,
@ -668,7 +725,11 @@ static void kvm_virtio_pci_vector_poll(PCIDevice *dev,
}
vq = virtio_get_queue(vdev, queue_no);
notifier = virtio_queue_get_guest_notifier(vq);
if (event_notifier_test_and_clear(notifier)) {
if (vdev->guest_notifier_pending) {
if (vdev->guest_notifier_pending(vdev, queue_no)) {
msix_set_pending(dev, vector);
}
} else if (event_notifier_test_and_clear(notifier)) {
msix_set_pending(dev, vector);
}
}

13
hw/virtio.h
View file

@ -126,6 +126,19 @@ struct VirtIODevice
void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
void (*reset)(VirtIODevice *vdev);
void (*set_status)(VirtIODevice *vdev, uint8_t val);
/* Test and clear event pending status.
* Should be called after unmask to avoid losing events.
* If backend does not support masking,
* must check in frontend instead.
*/
bool (*guest_notifier_pending)(VirtIODevice *vdev, int n);
/* Mask/unmask events from this vq. Any events reported
* while masked will become pending.
* If backend does not support masking,
* must mask in frontend instead.
*/
void (*guest_notifier_mask)(VirtIODevice *vdev, int n, bool mask);
VirtQueue *vq;
const VirtIOBindings *binding;
DeviceState *binding_opaque;