sched, trace: Add a tracepoint for IPI-less remote wakeups

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@amacapital.net>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: umgwanakikbuti@gmail.com
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/16205aee116772aa686814f9b13bccb562108047.1401902905.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 24 insertions, 0 deletions

diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 67e1bbf83695..0a68d5ae584e 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_idle_without_ipi,
+
+        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 5976ca579d3e..e4c0ddd3db8e 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_idle_without_ipi(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_idle_without_ipi(cpu);
 }
 
 static bool wake_up_full_nohz_cpu(int cpu)