[PATCH] perf/core: Add a tracepoint for perf sampling

[Brendan Gregg <bgregg@netflix.com>]

When perf is performing hrtimer-based sampling, this tracepoint can be used
by BPF to run additional logic on each sample. For example, BPF can fetch
stack traces and frequency count them in kernel context, for an efficient
profiler.

Signed-off-by: Brendan Gregg <bgregg@netflix.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
---
 include/trace/events/perf.h | 29 +++++++++++++++++++++++++++++
 kernel/events/core.c        |  5 +++++
 2 files changed, 34 insertions(+)
 create mode 100644 include/trace/events/perf.h

diff --git a/include/trace/events/perf.h b/include/trace/events/perf.h
new file mode 100644
index 0000000..461770d
--- /dev/null
+++ b/include/trace/events/perf.h
@@ -0,0 +1,29 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM perf
+
+#if !defined(_TRACE_PERF_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_PERF_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(perf_hrtimer,
+	TP_PROTO(struct pt_regs *regs, struct perf_event *event),
+
+	TP_ARGS(regs, event),
+
+	TP_STRUCT__entry(
+		__field(struct pt_regs *, regs)
+		__field(struct perf_event *, event)
+	),
+
+	TP_fast_assign(
+		__entry->regs = regs;
+		__entry->event = event;
+	),
+
+	TP_printk("regs=%p evt=%p", __entry->regs, __entry->event)
+);
+#endif /* _TRACE_PERF_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 79dae18..0d843a7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -51,6 +51,9 @@
 
 #include <asm/irq_regs.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/perf.h>
+
 typedef int (*remote_function_f)(void *);
 
 struct remote_function_call {
@@ -8036,6 +8039,8 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 	perf_sample_data_init(&data, 0, event->hw.last_period);
 	regs = get_irq_regs();
 
+	trace_perf_hrtimer(regs, event);
+
 	if (regs && !perf_exclude_event(event, regs)) {
 		if (!(event->attr.exclude_idle && is_idle_task(current)))
 			if (__perf_event_overflow(event, 1, &data, regs))
-- 
2.7.4