sched: HMP: Additional trace points for debugging HMP behaviour

1. Replace magic numbers in code for migration trace.
   Trace points still emit a number as force=<n> field:
     force=0 : wakeup migration
     force=1 : forced migration
     force=2 : offload migration
     force=3 : idle pull migration

2. Add trace to expose offload decision-making.
   Also adds tracing rq->nr_running so that you can
   look back to see what state the RQ was in at the time.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

2 files changed, 95 insertions, 10 deletions

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 203e8e9933b..66dc53bca19 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -530,6 +530,29 @@ TRACE_EVENT(sched_rq_runnable_load,
 			__entry->load)
 );
 
+TRACE_EVENT(sched_rq_nr_running,
+
+	TP_PROTO(int cpu, unsigned int nr_running, int nr_iowait),
+
+	TP_ARGS(cpu, nr_running, nr_iowait),
+
+	TP_STRUCT__entry(
+		__field(int, cpu)
+		__field(unsigned int, nr_running)
+		__field(int, nr_iowait)
+	),
+
+	TP_fast_assign(
+		__entry->cpu  = cpu;
+		__entry->nr_running = nr_running;
+		__entry->nr_iowait = nr_iowait;
+	),
+
+	TP_printk("cpu=%d nr_running=%u nr_iowait=%d",
+			__entry->cpu,
+			__entry->nr_running, __entry->nr_iowait)
+);
+
 /*
  * Tracepoint for showing tracked task cpu usage ratio [0..1023].
  */
@@ -559,6 +582,10 @@ TRACE_EVENT(sched_task_usage_ratio,
 /*
  * Tracepoint for HMP (CONFIG_SCHED_HMP) task migrations.
  */
+#define HMP_MIGRATE_WAKEUP 0
+#define HMP_MIGRATE_FORCE  1
+#define HMP_MIGRATE_OFFLOAD 2
+#define HMP_MIGRATE_IDLE_PULL 3
 TRACE_EVENT(sched_hmp_migrate,
 
 	TP_PROTO(struct task_struct *tsk, int dest, int force),
@@ -583,6 +610,51 @@ TRACE_EVENT(sched_hmp_migrate,
 			__entry->comm, __entry->pid,
 			__entry->dest, __entry->force)
 );
+
+TRACE_EVENT(sched_hmp_offload_abort,
+
+	TP_PROTO(int cpu, int data, char *label),
+
+	TP_ARGS(cpu,data,label),
+
+	TP_STRUCT__entry(
+		__array(char, label, 64)
+		__field(int, cpu)
+		__field(int, data)
+	),
+
+	TP_fast_assign(
+		strncpy(__entry->label, label, 64);
+		__entry->cpu   = cpu;
+		__entry->data = data;
+	),
+
+	TP_printk("cpu=%d data=%d label=%63s",
+			__entry->cpu, __entry->data,
+			__entry->label)
+);
+
+TRACE_EVENT(sched_hmp_offload_succeed,
+
+	TP_PROTO(int cpu, int dest_cpu),
+
+	TP_ARGS(cpu,dest_cpu),
+
+	TP_STRUCT__entry(
+		__field(int, cpu)
+		__field(int, dest_cpu)
+	),
+
+	TP_fast_assign(
+		__entry->cpu   = cpu;
+		__entry->dest_cpu = dest_cpu;
+	),
+
+	TP_printk("cpu=%d dest=%d",
+			__entry->cpu,
+			__entry->dest_cpu)
+);
+
 #endif /* _TRACE_SCHED_H */
 
 /* This part must be outside protection */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 62a93c62a84..78c9307b6ad 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1688,6 +1688,7 @@ static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
 	__update_tg_runnable_avg(&rq->avg, &rq->cfs);
 	trace_sched_rq_runnable_ratio(cpu_of(rq), rq->avg.load_avg_ratio);
 	trace_sched_rq_runnable_load(cpu_of(rq), rq->cfs.runnable_load_avg);
+	trace_sched_rq_nr_running(cpu_of(rq), rq->nr_running, rq->nr_iowait.counter);
 }
 
 /* Add the load generated by se into cfs_rq's child load-average */
@@ -4023,25 +4024,37 @@ static inline unsigned int hmp_offload_down(int cpu, struct sched_entity *se)
 
 	/* Is there an idle CPU in the current domain */
 	min_usage = hmp_domain_min_load(hmp_cpu_domain(cpu), NULL);
-	if (min_usage == 0)
+	if (min_usage == 0) {
+		trace_sched_hmp_offload_abort(cpu, min_usage, "load");
 		return NR_CPUS;
+	}
 
 	/* Is the task alone on the cpu? */
-	if (cpu_rq(cpu)->cfs.h_nr_running < 2)
+	if (cpu_rq(cpu)->cfs.h_nr_running < 2) {
+		trace_sched_hmp_offload_abort(cpu,
+			cpu_rq(cpu)->cfs.h_nr_running, "nr_running");
 		return NR_CPUS;
+	}
 
 	/* Is the task actually starving? */
 	/* >=25% ratio running/runnable = starving */
-	if (hmp_task_starvation(se) > 768)
+	if (hmp_task_starvation(se) > 768) {
+		trace_sched_hmp_offload_abort(cpu, hmp_task_starvation(se),
+			"starvation");
 		return NR_CPUS;
+	}
 
 	/* Does the slower domain have any idle CPUs? */
 	min_usage = hmp_domain_min_load(hmp_slower_domain(cpu), &dest_cpu);
-	if (min_usage > 0)
+	if (min_usage > 0) {
+		trace_sched_hmp_offload_abort(cpu, min_usage, "slowdomain");
 		return NR_CPUS;
+	}
 
-	if (cpumask_test_cpu(dest_cpu, &hmp_slower_domain(cpu)->cpus))
+	if (cpumask_test_cpu(dest_cpu, &hmp_slower_domain(cpu)->cpus)) {
+		trace_sched_hmp_offload_succeed(cpu, dest_cpu);
 		return dest_cpu;
+	}
 
 	return NR_CPUS;
 }
@@ -4178,13 +4191,13 @@ unlock:
 #ifdef CONFIG_SCHED_HMP
 	if (hmp_up_migration(prev_cpu, &new_cpu, &p->se)) {
 		hmp_next_up_delay(&p->se, new_cpu);
-		trace_sched_hmp_migrate(p, new_cpu, 0);
+		trace_sched_hmp_migrate(p, new_cpu, HMP_MIGRATE_WAKEUP);
 		return new_cpu;
 	}
 	if (hmp_down_migration(prev_cpu, &p->se)) {
 		new_cpu = hmp_select_slower_cpu(p, prev_cpu);
 		hmp_next_down_delay(&p->se, new_cpu);
-		trace_sched_hmp_migrate(p, new_cpu, 0);
+		trace_sched_hmp_migrate(p, new_cpu, HMP_MIGRATE_WAKEUP);
 		return new_cpu;
 	}
 	/* Make sure that the task stays in its previous hmp domain */
@@ -6822,7 +6835,7 @@ static void hmp_force_up_migration(int this_cpu)
 				target->push_cpu = target_cpu;
 				target->migrate_task = p;
 				force = 1;
-				trace_sched_hmp_migrate(p, target->push_cpu, 1);
+				trace_sched_hmp_migrate(p, target->push_cpu, HMP_MIGRATE_FORCE);
 				hmp_next_up_delay(&p->se, target->push_cpu);
 			}
 		}
@@ -6838,7 +6851,7 @@ static void hmp_force_up_migration(int this_cpu)
 				target->active_balance = 1;
 				target->migrate_task = p;
 				force = 1;
-				trace_sched_hmp_migrate(p, target->push_cpu, 2);
+				trace_sched_hmp_migrate(p, target->push_cpu, HMP_MIGRATE_OFFLOAD);
 				hmp_next_down_delay(&p->se, target->push_cpu);
 			}
 		}
@@ -6917,7 +6930,7 @@ static unsigned int hmp_idle_pull(int this_cpu)
 		target->push_cpu = this_cpu;
 		target->migrate_task = p;
 		force = 1;
-		trace_sched_hmp_migrate(p, target->push_cpu, 3);
+		trace_sched_hmp_migrate(p, target->push_cpu, HMP_MIGRATE_IDLE_PULL);
 		hmp_next_up_delay(&p->se, target->push_cpu);
 	}
 	raw_spin_unlock_irqrestore(&target->lock, flags);