[PATCH v2 2/5] sched,trace: Add a tracepoint for IPI-less remote wakeups

Andy Lutomirski
2014-06-04T17:32:36Z

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>
---
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..0a68d5a 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 321d800..a002be7 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)
--
1.9.3