sched/numa: Stop multiple tasks from moving to the cpu at the same time

Task migration under numa balancing can happen in parallel. More than
one task might choose to migrate to the same cpu at the same time. This
can result in
- During task swap, choosing a task that was not part of the evaluation.
- During task swap, task which just got moved into its preferred node,
  moving to a completely different node.
- During task swap, task failing to move to the preferred node, will have
  to wait an extra interval for the next migrate opportunity.
- During task movement, multiple task movements can cause load imbalance.

This problem is more likely if there are more cores per node or more
nodes in the system.

Use a per run-queue variable to check if numa-balance is active on the
run-queue.

specjbb2005 / bops/JVM / higher bops are better
on 2 Socket/2 Node Intel
JVMS  Prev    Current  %Change
4     199709  206350   3.32534
1     330830  319963   -3.28477

on 2 Socket/4 Node Power8 (PowerNV)
JVMS  Prev     Current  %Change
8     89011.9  89627.8  0.69193
1     218946   211338   -3.47483

on 2 Socket/2 Node Power9 (PowerNV)
JVMS  Prev    Current  %Change
4     180473  186539   3.36117
1     212805  220344   3.54268

on 4 Socket/4 Node Power7
JVMS  Prev     Current  %Change
8     56941.8  56836    -0.185804
1     111686   112970   1.14965

dbench / transactions / higher numbers are better
on 2 Socket/2 Node Intel
count  Min      Max      Avg      Variance  %Change
5      12029.8  12124.6  12060.9  34.0076
5      13136.1  13170.2  13150.2  14.7482   9.03166

on 2 Socket/4 Node Power8 (PowerNV)
count  Min      Max      Avg      Variance  %Change
5      4968.51  5006.62  4981.31  13.4151
5      4319.79  4998.19  4836.53  261.109   -2.90646

on 2 Socket/2 Node Power9 (PowerNV)
count  Min      Max      Avg      Variance  %Change
5      9342.92  9381.44  9363.92  12.8587
5      9325.56  9402.7   9362.49  25.9638   -0.0152714

on 4 Socket/4 Node Power7
count  Min      Max      Avg      Variance  %Change
5      143.4    188.892  170.225  16.9929
5      132.581  191.072  170.554  21.6444   0.193274

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1533276841-16341-2-git-send-email-srikar@linux.vnet.ibm.com