[PATCH 17/18] sched: Tracepoint task movement

[Mel Gorman]

move_task() is called from move_one_task and move_tasks and is an
approximation of load balancer activity. We should be able to track
tasks that move between CPUs frequently. If the tracepoint included node
information then we could distinguish between in-node and between-node
traffic for load balancer decisions. The tracepoint allows us to track
local migrations, remote migrations and average task migrations.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 include/trace/events/sched.h | 35 +++++++++++++++++++++++++++++++++++
 kernel/sched/fair.c          |  2 ++
 2 files changed, 37 insertions(+)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 04c3084..cf1694c 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -443,6 +443,41 @@ TRACE_EVENT(sched_process_hang,
 );
 #endif /* CONFIG_DETECT_HUNG_TASK */
 
+/*
+ * Tracks migration of tasks from one runqueue to another. Can be used to
+ * detect if automatic NUMA balancing is bouncing between nodes
+ */
+TRACE_EVENT(sched_move_task,
+
+	TP_PROTO(struct task_struct *tsk, int src_cpu, int dst_cpu),
+
+	TP_ARGS(tsk, src_cpu, dst_cpu),
+
+	TP_STRUCT__entry(
+		__field( pid_t,	pid			)
+		__field( pid_t,	tgid			)
+		__field( pid_t,	ngid			)
+		__field( int,	src_cpu			)
+		__field( int,	src_nid			)
+		__field( int,	dst_cpu			)
+		__field( int,	dst_nid			)
+	),
+
+	TP_fast_assign(
+		__entry->pid		= task_pid_nr(tsk);
+		__entry->tgid		= task_tgid_nr(tsk);
+		__entry->ngid		= task_numa_group_id(tsk);
+		__entry->src_cpu	= src_cpu;
+		__entry->src_nid	= cpu_to_node(src_cpu);
+		__entry->dst_cpu	= dst_cpu;
+		__entry->dst_nid	= cpu_to_node(dst_cpu);
+	),
+
+	TP_printk("pid=%d tgid=%d ngid=%d src_cpu=%d src_nid=%d dst_cpu=%d dst_nid=%d",
+			__entry->pid, __entry->tgid, __entry->ngid,
+			__entry->src_cpu, __entry->src_nid,
+			__entry->dst_cpu, __entry->dst_nid)
+);
 #endif /* _TRACE_SCHED_H */
 
 /* This part must be outside protection */
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ce1615..41021c8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4770,6 +4770,8 @@ static void move_task(struct task_struct *p, struct lb_env *env)
 	set_task_cpu(p, env->dst_cpu);
 	activate_task(env->dst_rq, p, 0);
 	check_preempt_curr(env->dst_rq, p, 0);
+
+	trace_sched_move_task(p, env->src_cpu, env->dst_cpu);
 }
 
 /*
-- 
1.8.4

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