From: Jamal Hadi [off-list ref]
   Date: Mon, 9 Jun 2003 08:18:50 -0400 (EDT)
   
   I found in my tests with a ethernet driver that prefetching the
   _next_ dma descriptor gave better numbers than prefetching the
   current one but i didnt spend too much time.

Two issues:

1) We have some cycles to borrow for head entry, we can make
   prefetch right before rcu_read_lock()

2) Ideally, hash chains will not exceed 1 (2 at the max)
   entries.

Just some thinking...