and performance impact.

The reason for a reworked governor is that there have been serious
performance issues reported with the existing code on Nehalem server
systems.

To show this I'm sure Andrew wants to see benchmark results:
(benchmark is "fio", "no cstates" is using "idle=poll")

		no cstates	current linux	new algorithm
1 disk		107 Mb/s	85 Mb/s		105 Mb/s
2 disks		215 Mb/s	123 Mb/s	209 Mb/s
12 disks	590 Mb/s	320 Mb/s	585 Mb/s

In various power benchmark measurements, no degredation was found by our
measurement&diagnostics team.  Obviously a bit more power was used in the
"fio" benchmark, due to the much higher performance.

The integration plan for this is to first add the new governor, but for
one kernel generation, leave the old menu governor in place so that it's
possible to separate out behavior from this governor versus other things
in diagnostics.  If no issues are found, I'll remove the old governor in
the kernel cycle after that.

While it would be a novel idea to describe the new algorithm in this
commit message, I cheaped out and described it in comments in the code
instead.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yanmin Zhang <yanmin_zhang@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>