[RFC] Fair-user scheduler

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

Current Linux CPU scheduler doesnt recognize process aggregates while
allocating bandwidth. As a result of this, an user could simply spawn large 
number of processes and get more bandwidth than others.

Here's a patch that provides fair allocation for all users in a system.

Some benchmark numbers with and without the patch applied follows:


		 	user "vatsa"		    user "guest"
		    (make -s -j4 bzImage)      (make -s -j20 bzImage)

2.6.20-rc5		472.07s (real)		   257.48s (real)
2.6.20-rc5+fairsched	766.74s (real)		   766.73s (real)


(Numbers taken on a 2way Intel x86_64 box)

Eventually something like this can be extended to do weighted fair share
scheduling for:

	- KVM
	- containers
	- resource management

Salient features of the patch:

	- Based on Ingo's RTLIMIT_RT_CPU patch [1]. Primary difference between 
	  RTLIMIT_RT_CPU patch and this one is that this patch handles 
	  starvation of lower priority tasks in a group and also accounting
	  is token based (rather than decaying avg).

	- Retains existing one-runqueue-per-cpu design

	- breaks O(1) (ouch!)
		Best way to avoid this is to split runqueue to be per-user and
		per-cpu, which I have not implemented to keep the patch simple.

	- Fairsched aware SMP load balance NOT addressed (yet)

Comments/flames wellcome!


References:

1. http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.11-rc2/2.6.11-rc2-mm2/broken-out/rlimit_rt_cpu.patch

-- 
Regards,
vatsa