Optimize for the MSI-X enabled and vector unmasked case where it is
possible to issue the KVM ioctl() directly instead of using irqfd.
This patch introduces a new virtio binding function which tries to
notify in a thread-safe way. If this is not possible, the function
returns false. Virtio block then knows to use irqfd as a fallback.
---
hw/msix.c | 17 +++++++++++++++++
hw/msix.h | 1 +
hw/virtio-blk.c | 10 ++++++++--
hw/virtio-pci.c | 8 ++++++++
hw/virtio.c | 9 +++++++++
hw/virtio.h | 3 +++
6 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/hw/msix.c b/hw/msix.c
index 7955221..3308604 100644
--- a/hw/msix.c
+++ b/hw/msix.c
@@ -503,6 +503,23 @@ void msix_notify(PCIDevice *dev, unsigned vector)
stl_le_phys(address, data);
}
+bool msix_try_notify_from_thread(PCIDevice *dev, unsigned vector)
+{
+ if (unlikely(vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector])) {
+ return false;
+ }
+ if (unlikely(msix_is_masked(dev, vector))) {
+ return false;
+ }
+#ifdef KVM_CAP_IRQCHIP
+ if (likely(kvm_enabled() && kvm_irqchip_in_kernel())) {
+ kvm_set_irq(dev->msix_irq_entries[vector].gsi, 1, NULL);
+ return true;
+ }
+#endif
+ return false;
+}
+
void msix_reset(PCIDevice *dev)
{
if (!(dev->cap_present & QEMU_PCI_CAP_MSIX))
diff --git a/hw/msix.h b/hw/msix.h
index a8661e1..99fb08f 100644
--- a/hw/msix.h
+++ b/hw/msix.h
@@ -26,6 +26,7 @@ void msix_vector_unuse(PCIDevice *dev, unsigned vector);
void msix_unuse_all_vectors(PCIDevice *dev);
void msix_notify(PCIDevice *dev, unsigned vector);
+bool msix_try_notify_from_thread(PCIDevice *dev, unsigned vector);
void msix_reset(PCIDevice *dev);
diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index bdff68a..efeffa0 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -82,6 +82,12 @@ static void virtio_blk_notify_guest(VirtIOBlock *s)
!(s->vdev.guest_features & (1 << VIRTIO_F_NOTIFY_ON_EMPTY))))
return;
+ /* Try to issue the ioctl() directly for speed */
+ if (likely(virtio_queue_try_notify_from_thread(s->vq))) {
+ return;
+ }
+
+ /* If the fast path didn't work, use irqfd */
event_notifier_set(virtio_queue_get_guest_notifier(s->vq));
}
@@ -263,7 +269,7 @@ static void data_plane_start(VirtIOBlock *s)
vring_setup(&s->vring, &s->vdev, 0);
/* Set up guest notifier (irq) */
- if (s->vdev.binding->set_guest_notifier(s->vdev.binding_opaque, 0, true) != 0) {
+ if (s->vdev.binding->set_guest_notifiers(s->vdev.binding_opaque, true) != 0) {
fprintf(stderr, "virtio-blk failed to set guest notifier, ensure -enable-kvm is set\n");
exit(1);
}
@@ -315,7 +321,7 @@ static void data_plane_stop(VirtIOBlock *s)
event_poll_cleanup(&s->event_poll);
/* Clean up guest notifier (irq) */
- s->vdev.binding->set_guest_notifier(s->vdev.binding_opaque, 0, false);
+ s->vdev.binding->set_guest_notifiers(s->vdev.binding_opaque, false);
}
static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t val)
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index f1e13af..03512b3 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -106,6 +106,13 @@ static void virtio_pci_notify(void *opaque, uint16_t vector)
qemu_set_irq(proxy->pci_dev.irq[0], proxy->vdev->isr & 1);
}
+static bool virtio_pci_try_notify_from_thread(void *opaque, uint16_t vector)
+{
+ VirtIOPCIProxy *proxy = opaque;
+ return msix_enabled(&proxy->pci_dev) &&
+ msix_try_notify_from_thread(&proxy->pci_dev, vector);
+}
+
static void virtio_pci_save_config(void * opaque, QEMUFile *f)
{
VirtIOPCIProxy *proxy = opaque;
@@ -707,6 +714,7 @@ static void virtio_pci_vmstate_change(void *opaque, bool running)
static const VirtIOBindings virtio_pci_bindings = {
.notify = virtio_pci_notify,
+ .try_notify_from_thread = virtio_pci_try_notify_from_thread,
.save_config = virtio_pci_save_config,
.load_config = virtio_pci_load_config,
.save_queue = virtio_pci_save_queue,
diff --git a/hw/virtio.c b/hw/virtio.c
index 064aecf..a1d1a8a 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -689,6 +689,15 @@ static inline int vring_need_event(uint16_t event, uint16_t new, uint16_t old)
return (uint16_t)(new - event - 1) < (uint16_t)(new - old);
}
+bool virtio_queue_try_notify_from_thread(VirtQueue *vq)
+{
+ VirtIODevice *vdev = vq->vdev;
+ if (likely(vdev->binding->try_notify_from_thread)) {
+ return vdev->binding->try_notify_from_thread(vdev->binding_opaque, vq->vector);
+ }
+ return false;
+}
+
static bool vring_notify(VirtIODevice *vdev, VirtQueue *vq)
{
uint16_t old, new;
diff --git a/hw/virtio.h b/hw/virtio.h
index 400c092..2cdf2be 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -93,6 +93,7 @@ typedef struct VirtQueueElement
typedef struct {
void (*notify)(void * opaque, uint16_t vector);
+ bool (*try_notify_from_thread)(void * opaque, uint16_t vector);
void (*save_config)(void * opaque, QEMUFile *f);
void (*save_queue)(void * opaque, int n, QEMUFile *f);
int (*load_config)(void * opaque, QEMUFile *f);
@@ -160,6 +161,8 @@ void virtio_cleanup(VirtIODevice *vdev);
void virtio_notify_config(VirtIODevice *vdev);
+bool virtio_queue_try_notify_from_thread(VirtQueue *vq);
+
void virtio_queue_set_notification(VirtQueue *vq, int enable);
int virtio_queue_ready(VirtQueue *vq);
--
1.7.10.4
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