sched: add tracepoints related to NUMA task migration

This patch adds three tracepoints
 o trace_sched_move_numa	when a task is moved to a node
 o trace_sched_swap_numa	when a task is swapped with another task
 o trace_sched_stick_numa	when a numa-related migration fails

The tracepoints allow the NUMA scheduler activity to be monitored and the
following high-level metrics can be calculated

 o NUMA migrated stuck	 nr trace_sched_stick_numa
 o NUMA migrated idle	 nr trace_sched_move_numa
 o NUMA migrated swapped nr trace_sched_swap_numa
 o NUMA local swapped	 trace_sched_swap_numa src_nid == dst_nid (should never happen)
 o NUMA remote swapped	 trace_sched_swap_numa src_nid != dst_nid (should == NUMA migrated swapped)
 o NUMA group swapped	 trace_sched_swap_numa src_ngid == dst_ngid
			 Maybe a small number of these are acceptable
			 but a high number would be a major surprise.
			 It would be even worse if bounces are frequent.
 o NUMA avg task migs.	 Average number of migrations for tasks
 o NUMA stddev task mig	 Self-explanatory
 o NUMA max task migs.	 Maximum number of migrations for a single task

In general the intent of the tracepoints is to help diagnose problems
where automatic NUMA balancing appears to be doing an excessive amount
of useless work.

[akpm@linux-foundation.org: remove semicolon-after-if, repair coding-style]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sched/fair.c

@@ -1250,11 +1250,15 @@ static int task_numa_migrate(struct task_struct *p)
 	p->numa_scan_period = task_scan_min(p);
 
 	if (env.best_task == NULL) {
-		int ret = migrate_task_to(p, env.best_cpu);
+		ret = migrate_task_to(p, env.best_cpu);
+		if (ret != 0)
+			trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
 		return ret;
 	}
 
 	ret = migrate_swap(p, env.best_task);
+	if (ret != 0)
+		trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
 	put_task_struct(env.best_task);
 	return ret;
 }