RFC sched: simplify the select_task_rq_fair()

v3 change log:
Fix small logical issues (Thanks to Mike Galbraith). Change the way of handling WAKE.

This patch set is trying to simplify the select_task_rq_fair() with schedule balance map.

After get rid of the complex code and reorganize the logical, pgbench show the improvement, more the clients, bigger the improvement.

				Prev:		Post:

	| db_size | clients |	|  tps  |	|  tps  |
        +---------+---------+   +-------+       +-------+
        | 22 MB   |       1 |   | 10788 |       | 10881 |
        | 22 MB   |       2 |   | 21617 |       | 21837 |
        | 22 MB   |       4 |   | 41597 |       | 42645 |
        | 22 MB   |       8 |   | 54622 |       | 57808 |
        | 22 MB   |      12 |   | 50753 |       | 54527 |
        | 22 MB   |      16 |   | 50433 |       | 56368 |	+11.77%
        | 22 MB   |      24 |   | 46725 |       | 54319 |	+16.25%
        | 22 MB   |      32 |   | 43498 |       | 54650 |	+25.64%
        | 7484 MB |       1 |   |  7894 |       |  8301 |
        | 7484 MB |       2 |   | 19477 |       | 19622 |
        | 7484 MB |       4 |   | 36458 |       | 38242 |
        | 7484 MB |       8 |   | 48423 |       | 50796 |
        | 7484 MB |      12 |   | 46042 |       | 49938 |
        | 7484 MB |      16 |   | 46274 |       | 50507 |	+9.15%
        | 7484 MB |      24 |   | 42583 |       | 49175 |	+15.48%
        | 7484 MB |      32 |   | 36413 |       | 49148 |	+34.97%
        | 15 GB   |       1 |   |  7742 |       |  7876 |
        | 15 GB   |       2 |   | 19339 |       | 19531 |
        | 15 GB   |       4 |   | 36072 |       | 37389 |
        | 15 GB   |       8 |   | 48549 |       | 50570 |
        | 15 GB   |      12 |   | 45716 |       | 49542 |
        | 15 GB   |      16 |   | 46127 |       | 49647 |	+7.63%
        | 15 GB   |      24 |   | 42539 |       | 48639 |	+14.34%
        | 15 GB   |      32 |   | 36038 |       | 48560 |	+34.75%

Please check the patch for more details about schedule balance map.

Support the NUMA domain but not well tested.
Support the rebuild of domain but not tested.

Comments are very welcomed.

Behind the v3:
Some changes has been applied to the way of handling WAKE.

And that's all around one question, whether we should do load balance for WAKE or not?

In the old world, the only chance to do load balance for WAKE is when prev cpu and curr cpu are not cache affine, but that doesn't make sense.

I suppose the real meaning behind that logical is, do balance only if cache benefit nothing after changing cpu.

However, select_idle_sibling() is not only designed for the purpose to take care of cache, it also benefit latency, and cost less than the balance path.

Besides, it's impossible to estimate the benefit of doing load balance at that point of time.

And that's come out the v3, no load balance for WAKE.

Test with:

	12 cpu X86 server and linux-next 3.8.0-rc3.

Michael Wang (3):
[RFC PATCH v3 1/3] sched: schedule balance map foundation
[RFC PATCH v3 2/3] sched: build schedule balance map
[RFC PATCH v3 3/3] sched: simplify select_task_rq_fair() with schedule balance map

---
 b/kernel/sched/core.c  |   44 +++++++++++++++
 b/kernel/sched/fair.c  |  135 ++++++++++++++++++++++++++-----------------------
 b/kernel/sched/sched.h |   14 +++++
 kernel/sched/core.c    |   67 ++++++++++++++++++++++++
 4 files changed, 199 insertions(+), 61 deletions(-)