[PATCH 2/6] sched,trace: Add a tracepoint for remote wakeups via polling

[Andy Lutomirski]

Remote wakeups of polling CPUs are a valuable performance
improvement; add a tracepoint to make it much easier to verify that
they're working.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
 include/trace/events/sched.h | 20 ++++++++++++++++++++
 kernel/sched/core.c          |  4 ++++
 2 files changed, 24 insertions(+)

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 67e1bbf..08f8632 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -530,6 +530,26 @@ TRACE_EVENT(sched_swap_numa,
 			__entry->dst_pid, __entry->dst_tgid, __entry->dst_ngid,
 			__entry->dst_cpu, __entry->dst_nid)
 );
+
+/*
+ * Tracepoint for waking a polling cpu without an IPI.
+ */
+TRACE_EVENT(sched_wake_polling_cpu,
+
+	TP_PROTO(int cpu),
+
+	TP_ARGS(cpu),
+
+	TP_STRUCT__entry(
+		__field(	int,	cpu	)
+	),
+
+	TP_fast_assign(
+		__entry->cpu	= cpu;
+	),
+
+	TP_printk("cpu=%d", __entry->cpu)
+);
 #endif /* _TRACE_SCHED_H */
 
 /* This part must be outside protection */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 321d800..18bebfc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -564,6 +564,8 @@ void resched_task(struct task_struct *p)
 
 	if (set_nr_and_not_polling(p))
 		smp_send_reschedule(cpu);
+	else
+		trace_sched_wake_polling_cpu(cpu);
 }
 
 void resched_cpu(int cpu)
@@ -647,6 +649,8 @@ static void wake_up_idle_cpu(int cpu)
 	smp_mb();
 	if (!tsk_is_polling(rq->idle))
 		smp_send_reschedule(cpu);
+	else
+		trace_sched_wake_polling_cpu(cpu);
 }
 
 static bool wake_up_full_nohz_cpu(int cpu)
-- 
1.9.3

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