On 01/12/2016 09:26 AM, Victor Kaplansky wrote:
This RFC PATCH tries to solve the problem of lost interrupts
>from a slow back-end. Didier could you test it?
Thanks, Victor
When interrupts are unmasked, it could take some undefined time
to the back-end to start routing events to guest_notifier. Till
that the events will continue flow to masked_notifier, and some
interrupts could be lost.
This patch tries to handle the above situation by testing and
cleaning both masked_notifier and guest_notifier in
guest_notifier read handler.
Signed-off-by: Victor Kaplansky <address@hidden>
---
include/hw/virtio/virtio.h | 1 +
hw/virtio/vhost.c | 3 +++
hw/virtio/virtio.c | 14 ++++++++++++++
3 files changed, 18 insertions(+)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 205fadf2..f52b0b6a 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -240,6 +240,7 @@ VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
uint16_t virtio_get_queue_index(VirtQueue *vq);
int virtio_queue_get_id(VirtQueue *vq);
EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq);
+void virtio_queue_set_masked_guest_notifier(VirtQueue *vq, EventNotifier *n);
void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
bool with_irqfd);
EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index de29968a..51ce1532 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -854,6 +854,9 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
/* Clear and discard previous events if any. */
event_notifier_test_and_clear(&vq->masked_notifier);
+ /* Set masked guest_notifier. */
+ virtio_queue_set_masked_guest_notifier(vvq, &vq->masked_notifier);
+
return 0;
fail_kick:
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index bd6b4df9..d9095c51 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -89,6 +89,7 @@ struct VirtQueue
VirtIODevice *vdev;
EventNotifier guest_notifier;
EventNotifier host_notifier;
+ EventNotifier *masked_guest_notifier;
QLIST_ENTRY(VirtQueue) node;
};
@@ -1622,6 +1623,14 @@ static void
virtio_queue_guest_notifier_read(EventNotifier *n)
if (event_notifier_test_and_clear(n)) {
virtio_irq(vq);
}
+ /* It could take some time to the backend to switch to
+ * sending to unmasked evenfd, so we have to test masked
+ * notifier too. */
+ if (vq->masked_guest_notifier) {
+ if (event_notifier_test_and_clear(vq->masked_guest_notifier)) {
+ virtio_irq(vq);
+ }
+ }
}
void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
@@ -1645,6 +1654,11 @@ EventNotifier *virtio_queue_get_guest_notifier(VirtQueue
*vq)
return &vq->guest_notifier;
}
+void virtio_queue_set_masked_guest_notifier(VirtQueue *vq, EventNotifier *n)
+{
+ vq->masked_guest_notifier = n;
+}
+
static void virtio_queue_host_notifier_read(EventNotifier *n)
{
VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
Hi viktor,
i'm wondering how this patch works.
virtio_queue_guest_notifier_read is only used in
virtio_queue_set_guest_notifier_fd_handler.
and it is only used if with_irq is not set:
if (assign && !with_irqfd) {
event_notifier_set_handler(&vq->guest_notifier,
virtio_queue_guest_notifier_read);
} else {
event_notifier_set_handler(&vq->guest_notifier, NULL);
}
else null handler is set in guest_notifier.
And from my understanding, virtio-pci in kvm mode uses irqfd, so when are
we entering the virtio_queue_guest_notifier_read?
did you also change the qemu configuration?