[RFC] [PATCH 0/3] Add group fairness to CFS

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

Here's an attempt to extend CFS (v13) to be fair at a group level, rather than
just at task level. The patch is in a very premature state (passes
simple tests, smp load balance not supported yet) at this point. I am sending 
it out early to know if this is a good direction to proceed.

Salient points which needs discussion:

1. This patch reuses CFS core to achieve fairness at group level also.

   To make this possible, CFS core has been abstracted to deal with generic 
   schedulable "entities" (tasks, users etc).

2. The per-cpu rb-tree has been split to be per-group per-cpu.

   schedule() now becomes two step on every cpu : pick a group first (from
   group rb-tree) and a task within that group next (from that group's task
   rb-tree)

3. Grouping mechanism - I have used 'uid' as the basis of grouping for
   timebeing (since that grouping concept is already in mainline today).
   The patch can be adapted to a more generic process grouping mechanism
   (like http://lkml.org/lkml/2007/4/27/146) later.

Some results below, obtained on a 4way (with HT) Intel Xeon box. All 
number are reflective of single CPU performance (tests were forced to 
run on single cpu since load balance is not yet supported).


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

2.6.22-rc1		          772.02 sec		497.42 sec (real)
2.6.22-rc1+cfs-v13 	          780.62 sec		478.35 sec (real)
2.6.22-rc1+cfs-v13+this patch     776.36 sec		776.68 sec (real)

[ An exclusive cpuset containing only one CPU was created and the
compilation jobs of both users were run simultaneously in this cpuset ]

I also disabled CONFIG_FAIR_USER_SCHED and compared the results with
cfs-v13:

					uid "vatsa"
					make -s -j4 bzImage

2.6.22-rc1+cfs-v13			395.57 sec (real)
2.6.22-rc1+cfs-v13+this_patch		388.54 sec (real)

There is no regression I can see (rather some improvement, which I can't
understand atm). I will run more tests later to check this regression aspect.

Request your comments on the future direction to proceed!


-- 
Regards,
vatsa