1. Split the QP spinlock into separate send and receive locks.

   The only place where we have to lock both is upon modify_qp, and
   that is not on data path.

2. Avoid taking any QP locks when polling CQ.

   This last part is achieved by getting rid of the cur field in
   mthca_wq, and calculating the number of outstanding WQEs by
   comparing the head and tail fields.  head is only updated by
   post, tail is only updated by poll.

   In a rare case where an overrun is detected, a CQ is locked and the
   overrun condition is re-tested, to avoid any potential for stale
   tail values.
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>