CPU Controller V2

Here's V2 of the token-based CPU controller I have been working on.

Changes since last version (posted at http://lkml.org/lkml/2006/8/20/115):

	- Task load was not changed when it moved between task-groups of
	  different quota (bug hit by Mike Galbraith).

	- SMP load balance seems to work -much- better now wrt its awaress
	  of quota on each task-group. The trick was to go beyond the
	  max_load difference in __move_tasks and instead use the load
	  difference between two task-groups on the different cpus as
	  basis of pulling tasks.

	- Better timeslice management, aimed at handling bursty
	  workloads better. Patch 3/9 has documentation on timeslice
	  management for various task-groups.

	- Modified cpuset interface as per Paul Jackson's suggestions.
	  Some of the changes are:
		- s/meter_cpu/cpu_meter_enabled
		- s/cpu_quota/cpu_meter_quota
		- s/FILE_METER_FLAG/FILE_CPU_METER_ENABLED
		- s/FILE_METER_QUOTA/FILE_CPU_METER_QUOTA
		- Dont allow cpu_meter_enabled to be turned on for an
		  "in-use" cpuset (which has tasks attached to it)
		- Dont allow cpu_meter_quota to be changed for an 
		  "in-use" cpuset (which has tasks attached to it)
		  
		  Last two are temporary limitations until we figure out how
		  to get to a cpuset's task-list more easily. 

Still on my todo list:

	- Improved surplus cycles management. If A, B and C groups have
	  been given 50%, 30% and 20%  quota respectively and if group B
	  is idle, B's quota has to be divided b/n A and C in the 5:2 
	  proportion.
	
	- Although load balance seems to be working nicely for the
	  testcases I have been running, I anticipate certain corner
	  cases which are yet to be worked out. Especially I need to
	  make sure some of the HT/MC optimizations are not broken.


Ingo/Nick, IMHO virtualizing cpu-runqueues approach to solve the controller 
need is not a good idea, since:

	- retaining existing load-balance optimizations for MC/SMT case is 
	  going to be hard (has to be done at schedule time now)
	- because of virtualization, two virtual cpus could end up running on 
	  the same physical cpu which would affect the carefull SMP 
	  optimizations put in place are all-over the kernel
	- not to mention specialized apps which want to bind to CPUs for 
	  performance reasons may behave badly in such a virtualized
	  environment.

Hence I have been pursuing more simpler approaches like in this patch.

Your comments/views on this are highly appreciated.

-- 
Regards,
vatsa