Commit 8d622d21 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

virtio: fix up virtio_disable_cb 



virtio_disable_cb is currently a nop for split ring with event index.
This is because it used to be always called from a callback when we know
device won't trigger more events until we update the index.  However,
now that we run with interrupts enabled a lot we also poll without a
callback so that is different: disabling callbacks will help reduce the
number of spurious interrupts.
Further, if using event index with a packed ring, and if being called
from a callback, we actually do disable interrupts which is unnecessary.

Fix both issues by tracking whenever we get a callback. If that is
the case disabling interrupts with event index can be a nop.
If not the case disable interrupts. Note: with a split ring
there's no explicit "no interrupts" value. For now we write
a fixed value so our chance of triggering an interupt
is 1/ring size. It's probably better to write something
related to the last used index there to reduce the chance
even further. For now I'm keeping it simple.

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 22bc63c5

drivers/virtio/virtio_ring.c

+25 −1
Original line number Diff line number Diff line
@@ -113,6 +113,9 @@ struct vring_virtqueue { 
	/* Last used index we've seen. */

	u16 last_used_idx;



	/* Hint for event idx: already triggered no need to disable. */

	bool event_triggered;



	union {

		/* Available for split ring */

		struct {
@@ -739,7 +742,10 @@ static void virtqueue_disable_cb_split(struct virtqueue *_vq) 


	if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {

		vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;

		if (!vq->event)

		if (vq->event)

			/* TODO: this is a hack. Figure out a cleaner value to write. */

			vring_used_event(&vq->split.vring) = 0x0;

		else

			vq->split.vring.avail->flags =

				cpu_to_virtio16(_vq->vdev,

						vq->split.avail_flags_shadow);
@@ -1605,6 +1611,7 @@ static struct virtqueue *vring_create_virtqueue_packed( 
	vq->weak_barriers = weak_barriers;

	vq->broken = false;

	vq->last_used_idx = 0;

	vq->event_triggered = false;

	vq->num_added = 0;

	vq->packed_ring = true;

	vq->use_dma_api = vring_use_dma_api(vdev);
@@ -1919,6 +1926,12 @@ void virtqueue_disable_cb(struct virtqueue *_vq) 
{

	struct vring_virtqueue *vq = to_vvq(_vq);



	/* If device triggered an event already it won't trigger one again:

	 * no need to disable.

	 */

	if (vq->event_triggered)

		return;



	if (vq->packed_ring)

		virtqueue_disable_cb_packed(_vq);

	else
@@ -1942,6 +1955,9 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) 
{

	struct vring_virtqueue *vq = to_vvq(_vq);



	if (vq->event_triggered)

		vq->event_triggered = false;



	return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) :

				 virtqueue_enable_cb_prepare_split(_vq);

}
@@ -2005,6 +2021,9 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) 
{

	struct vring_virtqueue *vq = to_vvq(_vq);



	if (vq->event_triggered)

		vq->event_triggered = false;



	return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) :

				 virtqueue_enable_cb_delayed_split(_vq);

}
@@ -2044,6 +2063,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq) 
	if (unlikely(vq->broken))

		return IRQ_HANDLED;



	/* Just a hint for performance: so it's ok that this can be racy! */

	if (vq->event)

		vq->event_triggered = true;



	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);

	if (vq->vq.callback)

		vq->vq.callback(&vq->vq);
@@ -2083,6 +2106,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index, 
	vq->weak_barriers = weak_barriers;

	vq->broken = false;

	vq->last_used_idx = 0;

	vq->event_triggered = false;

	vq->num_added = 0;

	vq->use_dma_api = vring_use_dma_api(vdev);

#ifdef DEBUG