Lockfree fd lookup 0 of 5

That won't help:
The problem is the cache line trashing from fget() and fget_light() with multithreaded apps. A sequence lock might help, but an rw lock is not a solution.
Actually: 2.4 had an rwlock, it was converted to a spinlock because spinlocks are faster on i386:

   read_lock();
   short operation();
   read_unlock();

is a bit slower than

   spin_lock();
   short operation();
   spin_unlock();

because read_unlock() is a full memory barrier and spin_unlock is not a memory barrier (not necessary because writes are ordered)

--
Manfred