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

On Sun, 15 May 2011 15:47:27 +0300, "Michael S. Tsirkin" [off-list ref] wrote:

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

quoted

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

quoted

 #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.

If we combine them into one, then these patches no longer depend on
the feature bit expansion, which is worthwhile (though I'll take both).

Thanks,
Rusty.