[RFC] 0/5 rcu lock update

[Manfred Spraul]

Hi,

I tried to tackle the rcu scalability problem that Jack Steiner
noticed:
I found three changes that reduce the cache line trashing with
rcu_ctrlblk:
- Use generation numbers instead of the rcu_cpu_mask bitmap for 
  polling in rcu_pending. (patch 1)
- Use a sequence lock to check if a new batch must be started.  Right
  now each cpu acquires the global spinlock and usually notices that
  the batch is already running. (patch 2)
- Hide implementation details - only fields that are accessed by
  rcu_pending need to be visible in <linux/rcupdate.h> (patch 3)
- Preparation for hierarchical bitmap : hide locking (patch 4)
- Add a hierarchical bitmap (patch 5)

The first three patches are IMHO steps in the right direction,
suitable for inclusion. The last two patches are proof of concept
changes.

--
	Manfred
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