Thread (4 messages) 4 messages, 2 authors, 2021-04-13

Re: [PATCH net] virtio-net: suppress bad irq warning for tx napi

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2021-04-12 22:33:54
Also in: netdev
Subsystem: networking drivers, the rest, virtio core, virtio net driver · Maintainers: Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, "Michael S. Tsirkin", Jason Wang

Possibly related (same subject, not in this thread)

On Mon, Apr 12, 2021 at 06:08:21PM -0400, Michael S. Tsirkin wrote:
OK I started looking at this again. My idea is simple.
A. disable callbacks before we try to drain skbs
B. actually do disable callbacks even with event idx

To make B not regress, we need to
C. detect the common case of disable after event triggering and skip the write then.

I added a new event_triggered flag for that.
Completely untested - but then I could not see the warnings either.
Would be very much interested to know whether this patch helps
resolve the sruprious interrupt problem at all ...


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Hmm a slightly cleaner alternative is to clear the flag when enabling interrupts ...
I wonder which cacheline it's best to use for this.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 82e520d2cb12..c23341b18eb5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1429,6 +1429,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
 		return;
 
 	if (__netif_tx_trylock(txq)) {
+		virtqueue_disable_cb(vq);
 		free_old_xmit_skbs(sq, true);
 		__netif_tx_unlock(txq);
 	}
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71e16b53e9c1..88f0b16b11b8 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
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help