On Sat, Jul 10, 2021 at 07:51:07PM -0400, Sasha Levin wrote:
From: "Michael S. Tsirkin" mst@redhat.com
[ Upstream commit 8d622d21d24803408b256d96463eac4574dcf067 ]
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: Michael S. Tsirkin mst@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org
I don't think we should have it in stable just yet. Let's make sure it fixes the issue first.
drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 97e8a195e18f..b6e1e0598529 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -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
2.30.2