virtio: force callback on empty.

virtio allows drivers to suppress callbacks (ie. interrupts) for efficiency (no locking, it's just an optimization). There's a similar mechanism for the host to suppress notifications coming from the guest: in that case, we ignore the suppression if the ring is completely full. It turns out that life is simpler if the host similarly ignores callback suppression when the ring is completely empty: the network driver wants to free up old packets in a timely manner, and otherwise has to use a timer to poll. We have to remove the code which ignores interrupts when the driver has disabled them (again, it had no locking and hence was unreliable anyway). Signed-off-by: Rusty Russell <[email protected]>
mgowda · May 30, 2008 · b4f68be · b4f68be
1 parent 7757f09
commit b4f68be
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Showing 2 changed files with 4 additions and 7 deletions.
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
@@ -253,13 +253,6 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 	if (unlikely(vq->broken))
 		return IRQ_HANDLED;
 
-	/* Other side may have missed us turning off the interrupt,
-	 * but we should preserve disable semantic for virtio users. */
-	if (unlikely(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
-		pr_debug("virtqueue interrupt after disable for %p\n", vq);
-		return IRQ_HANDLED;
-	}
-
 	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 	if (vq->vq.callback)
 		vq->vq.callback(&vq->vq);

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
@@ -15,6 +15,10 @@
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED		0x80
 
+/* Do we get callbacks when the ring is completely used, even if we've
+ * suppressed them? */
+#define VIRTIO_F_NOTIFY_ON_EMPTY	24
+
 #ifdef __KERNEL__
 #include <linux/virtio.h>