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>

include/linux/sched.h

@@ -921,6 +921,7 @@ struct sched_entity {
 	u64			block_start;
 	u64			block_max;
 	u64			exec_max;
+	u64			slice_max;
 
 	unsigned long		wait_runtime_overruns;
 	unsigned long		wait_runtime_underruns;

kernel/sched.c

@@ -1603,6 +1603,7 @@ static void __sched_fork(struct task_struct *p)
 	p->se.sleep_max			= 0;
 	p->se.block_max			= 0;
 	p->se.exec_max			= 0;
+	p->se.slice_max			= 0;
 	p->se.wait_max			= 0;
 	p->se.wait_runtime_overruns	= 0;
 	p->se.wait_runtime_underruns	= 0;

kernel/sched_debug.c

@@ -254,6 +254,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
 	P(se.sleep_max);
 	P(se.block_max);
 	P(se.exec_max);
+	P(se.slice_max);
 	P(se.wait_max);
 	P(se.wait_runtime_overruns);
 	P(se.wait_runtime_underruns);
@@ -282,6 +283,7 @@ void proc_sched_set_task(struct task_struct *p)
 	p->se.sleep_max			= 0;
 	p->se.block_max			= 0;
 	p->se.exec_max			= 0;
+	p->se.slice_max			= 0;
 	p->se.wait_max			= 0;
 	p->se.wait_runtime_overruns	= 0;
 	p->se.wait_runtime_underruns	= 0;

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;
 }