Re: [PATCH 06/18] virtio_ring: avail event index interface

On Mon, May 09, 2011 at 01:43:15PM +0930, Rusty Russell wrote:

On Wed, 4 May 2011 23:51:19 +0300, "Michael S. Tsirkin" [off-list ref] wrote:

quoted

Define a new feature bit for the host to
declare that it uses an avail_event index
(like Xen) instead of a feature bit
to enable/disable interrupts.

Signed-off-by: Michael S. Tsirkin <redacted>
---
 include/linux/virtio_ring.h |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index f5c1b75..f791772 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h

@@ -32,6 +32,9 @@
 /* The Guest publishes the used index for which it expects an interrupt
  * at the end of the avail ring. Host should ignore the avail->flags field. */
 #define VIRTIO_RING_F_USED_EVENT_IDX	29
+/* The Host publishes the avail index for which it expects a kick
+ * at the end of the used ring. Guest should ignore the used->flags field. */
+#define VIRTIO_RING_F_AVAIL_EVENT_IDX	32

Are you really sure we want to separate the two?  Seems a little simpler
to have one bit to mean "we're publishing our threshold".  For someone
implementing this from scratch, it's a little simpler.

Or are there cases where the old style makes more sense?

Thanks,
Rusty.

Hmm, it makes debugging easier as each side can disable
publishing separately - I used it all the time when I saw
e.g. networking stuck to guess whether I need to investigate the
interrupt or the exit handling.

But I'm not hung up on this.

Let me know pls.

-- 
MST