From: "Michael S. Tsirkin" <mst@mellanox.co.il>

Event queue handling performance improvements:
 - Only calculate EQ entry address once, and don't truncate the
   consumer index until we really need to.
 - Only read ECR once.  If a new event occurs while we're in the
   interrupt handler, we'll get another interrupt anyway, since we
   only clear events once.
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>