The relationship between INTERACTIVE_SLEEP and the ceiling is not perfect
and not explicit enough.  The sleep boost is not supposed to be any larger
than without this code and the comment is not clear enough about what
exactly it does, just the reason it does it.  Fix it.

There is a ceiling to the priority beyond which tasks that only ever sleep
for very long periods cannot surpass.  Fix it.

Prevent the on-runqueue bonus logic from defeating the idle sleep logic.

Opportunity to micro-optimise.
Signed-off-by: NCon Kolivas <kernel@kolivas.org>
Signed-off-by: NMike Galbraith <efault@gmx.de>
Acked-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NKen Chen <kenneth.w.chen@intel.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>