tree 9c8f356f6c294678a05dbc983e60b8b5d864b7bc
parent 674bfc23c585b34c42263d73fb51710d49762a23
author Rusty Russell <rusty@rustcorp.com.au> 1217005564 -0500
committer Rusty Russell <rusty@rustcorp.com.au> 1216951564 +1000

virtio: don't always force a notification when ring is full

We force notification when the ring is full, even if the host has
indicated it doesn't want to know.  This seemed like a good idea at
the time: if we fill the transmit ring, we should tell the host
immediately.

Unfortunately this logic also applies to the receiving ring, which is
refilled constantly.  We should introduce real notification thesholds
to replace this logic.  Meanwhile, removing the logic altogether breaks
the heuristics which KVM uses, so we use a hack: only notify if there are
outgoing parts of the new buffer.

Here are the number of exits with lguest's crappy network implementation:
Before:
	network xmit 7859051 recv 236420
After:
	network xmit 7858610 recv 118136

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>