On Thu, 2012-11-29 at 17:15 +0100, Jesper Dangaard Brouer wrote:

This patch implements per hash bucket locking for the frag queue
hash.  This removes two write locks, and the only remaining write
lock is for protecting hash rebuild.  This essentially reduce the
readers-writer lock to a rebuild lock.

So we still have this huge contention on the reader-writer lock cache
line...

I would just remove it. (And remove hash rebuild, or make it RCU
compatible )