[PATCH V3 2/6] perf/core: Add PERF_EVENT_IOC_STAT to control overhead statistics

[kan.liang@intel.com]

From: Kan Liang <kan.liang@intel.com>

It only needs to generate the overhead statistics once when perf is
done. But there is no good place in the kernel for that.

A new ioctl PERF_EVENT_IOC_STAT is introduced to notify the kernel when
the tool 'start' and 'done'.
In 'start', the kernel resets the overhead numbers.
In 'done', the kernel generates pmu's overhead.

It also needs a pmu specific int (*stat) to do the real work.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
 include/linux/perf_event.h      | 6 ++++++
 include/uapi/linux/perf_event.h | 3 +++
 kernel/events/core.c            | 5 +++++
 3 files changed, 14 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 946e8d8..a34f9a2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -403,6 +403,12 @@ struct pmu {
 	 */
 	void (*sched_task)		(struct perf_event_context *ctx,
 					bool sched_in);
+
+	/*
+	 * overhead statistics
+	 */
+	int (*stat)			(struct perf_event *event, u32 flag);
+
 	/*
 	 * PMU specific data size
 	 */
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 101f8b3..23b7963 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -408,9 +408,12 @@ struct perf_event_attr {
 #define PERF_EVENT_IOC_ID		_IOR('$', 7, __u64 *)
 #define PERF_EVENT_IOC_SET_BPF		_IOW('$', 8, __u32)
 #define PERF_EVENT_IOC_PAUSE_OUTPUT	_IOW('$', 9, __u32)
+#define PERF_EVENT_IOC_STAT		_IOW('$', 10, __u32)
 
 enum perf_event_ioc_flags {
 	PERF_IOC_FLAG_GROUP		= 1U << 0,
+	PERF_IOC_FLAG_STAT_START	= 1U << 1,
+	PERF_IOC_FLAG_STAT_DONE		= 1U << 2,
 };
 
 /*
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1420139..dbde193 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4637,6 +4637,11 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 		rcu_read_unlock();
 		return 0;
 	}
+	case PERF_EVENT_IOC_STAT: {
+		if (event->pmu->stat)
+			return event->pmu->stat(event, flags);
+		return 0;
+	}
 	default:
 		return -ENOTTY;
 	}
-- 
2.4.3