sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target

sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target

This patch adds checks that prevens futile attempts to move rt tasks
to a CPU with active tasks of equal or higher priority.

This reduces run queue lock contention and improves the performance of
a well known OLTP benchmark by 0.7%.

Signed-off-by: Tim Chen <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Shawn Bohrer <[email protected]>
Cc: Suruchi Kadu <[email protected]>
Cc: Doug Nelson<[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>