sunvnet: Reduce LDC message overhead.

This patch series has 2 sets of changes to reduce the overhead from LDC messages.

- the current linux sunvnet driver sends out many more LDC start and stop triggers than it needs to: when we are sending a burst of packets across multiple descriptor rings, we only need to send the "start" trigger for the first dring (we currently send one for every dring). And we only need to send the "STOPPED" trigger for the last dring (and if that fails, hold off and send the trigger later).

- When reading the descriptor rings, don't give up as soon as a dring that is not VIO_DESC_READY is found- especially when the peer is sending a burst of packets, it is worthwhile to recheck the descriptor status after a small microsecond delay, as the likelihood of finding this descriptor READY is high, and it is cheaper to just retry with a delay than to return from the current context, read another LDC message, and then come back to read this descriptor.

Sowmini Varadhan (2):
Avoid sending superfluous LDC messages.
Re-check for a VIO_DESC_READY data descriptor after short udelay()

 drivers/net/ethernet/sun/sunvnet.c | 87 ++++++++++++++++++++++++++++++++++----
 drivers/net/ethernet/sun/sunvnet.h |  4 ++
 2 files changed, 83 insertions(+), 8 deletions(-)

1.8.4.2