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 <rusty@rustcorp.com.au>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 96d2567a7df8cea095dcddae0331bb221834889b..72bf8bc090142f02a9065c0ff0448299a5e9a2e7 100644 (file)
--- 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
index 71d6c102497e1957c5374f926c437c51758c8894..f364bbf63c3413547738ae4028b399577bc76650 100644 (file)
--- 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>