sched: debug: track maximum 'slice'

track the maximum amount of time a task has executed while
the CPU load was at least 2x. (i.e. at least two nice-0
tasks were runnable)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched_fair.c

@@ -739,6 +739,17 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 	update_stats_wait_end(cfs_rq, se);
 	update_stats_curr_start(cfs_rq, se);
 	set_cfs_rq_curr(cfs_rq, se);
+#ifdef CONFIG_SCHEDSTATS
+	/*
+	 * Track our maximum slice length, if the CPU's load is at
+	 * least twice that of our own weight (i.e. dont track it
+	 * when there are only lesser-weight tasks around):
+	 */
+	if (rq_of(cfs_rq)->ls.load.weight >= 2*se->load.weight) {
+		se->slice_max = max(se->slice_max,
+			se->sum_exec_runtime - se->prev_sum_exec_runtime);
+	}
+#endif
 	se->prev_sum_exec_runtime = se->sum_exec_runtime;
 }