[RFC/PATCH 1/4] perf/core: Add PERF_FORMAT_DROPPED

[Namhyung Kim <namhyung@kernel.org>]

When a perf_event is dropped due to some kind of (SW-based) filter, it
won't generate sample data.  For example, software events drops samples
when it doesn't match to privilege from exclude_{user,kernel}.

In order to account such dropped samples, add a new counter in the
perf_event, and let users can read(2) the number with the new
PERF_FORMAT_DROPPED like the lost sample count.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 include/linux/perf_event.h      |  1 +
 include/uapi/linux/perf_event.h |  5 ++++-
 kernel/events/core.c            | 12 ++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 701549967c18..955d39543398 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -809,6 +809,7 @@ struct perf_event {
 	u64				id;
 
 	atomic64_t			lost_samples;
+	atomic64_t			dropped_samples;
 
 	u64				(*clock)(void);
 	perf_overflow_handler_t		overflow_handler;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 58daf6156fd0..6f19d4f74823 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -347,6 +347,7 @@ enum {
  *	  { u64		time_running; } && PERF_FORMAT_TOTAL_TIME_RUNNING
  *	  { u64		id;           } && PERF_FORMAT_ID
  *	  { u64		lost;         } && PERF_FORMAT_LOST
+ *	  { u64		dropped;      } && PERF_FORMAT_DROPPED
  *	} && !PERF_FORMAT_GROUP
  *
  *	{ u64		nr;
@@ -355,6 +356,7 @@ enum {
  *	  { u64		value;
  *	    { u64	id;           } && PERF_FORMAT_ID
  *	    { u64	lost;         } && PERF_FORMAT_LOST
+ *	    { u64	dropped;      } && PERF_FORMAT_DROPPED
  *	  }		cntr[nr];
  *	} && PERF_FORMAT_GROUP
  * };
@@ -365,8 +367,9 @@ enum perf_event_read_format {
 	PERF_FORMAT_ID				= 1U << 2,
 	PERF_FORMAT_GROUP			= 1U << 3,
 	PERF_FORMAT_LOST			= 1U << 4,
+	PERF_FORMAT_DROPPED			= 1U << 5,
 
-	PERF_FORMAT_MAX = 1U << 5,		/* non-ABI */
+	PERF_FORMAT_MAX = 1U << 6,		/* non-ABI */
 };
 
 #define PERF_ATTR_SIZE_VER0	64	/* sizeof first published struct */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c6a720f41225..4d72538628ee 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5679,6 +5679,8 @@ static int __perf_read_group_add(struct perf_event *leader,
 		values[n++] = primary_event_id(leader);
 	if (read_format & PERF_FORMAT_LOST)
 		values[n++] = atomic64_read(&leader->lost_samples);
+	if (read_format & PERF_FORMAT_DROPPED)
+		values[n++] = atomic64_read(&leader->dropped_samples);
 
 	for_each_sibling_event(sub, leader) {
 		values[n++] += perf_event_count(sub, false);
@@ -5686,6 +5688,8 @@ static int __perf_read_group_add(struct perf_event *leader,
 			values[n++] = primary_event_id(sub);
 		if (read_format & PERF_FORMAT_LOST)
 			values[n++] = atomic64_read(&sub->lost_samples);
+		if (read_format & PERF_FORMAT_DROPPED)
+			values[n++] = atomic64_read(&sub->dropped_samples);
 	}
 
 unlock:
@@ -5751,6 +5755,8 @@ static int perf_read_one(struct perf_event *event,
 		values[n++] = primary_event_id(event);
 	if (read_format & PERF_FORMAT_LOST)
 		values[n++] = atomic64_read(&event->lost_samples);
+	if (read_format & PERF_FORMAT_DROPPED)
+		values[n++] = atomic64_read(&event->dropped_samples);
 
 	if (copy_to_user(buf, values, n * sizeof(u64)))
 		return -EFAULT;
@@ -7348,6 +7354,8 @@ static void perf_output_read_one(struct perf_output_handle *handle,
 		values[n++] = primary_event_id(event);
 	if (read_format & PERF_FORMAT_LOST)
 		values[n++] = atomic64_read(&event->lost_samples);
+	if (read_format & PERF_FORMAT_DROPPED)
+		values[n++] = atomic64_read(&event->dropped_samples);
 
 	__output_copy(handle, values, n * sizeof(u64));
 }
@@ -7386,6 +7394,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 		values[n++] = primary_event_id(leader);
 	if (read_format & PERF_FORMAT_LOST)
 		values[n++] = atomic64_read(&leader->lost_samples);
+	if (read_format & PERF_FORMAT_DROPPED)
+		values[n++] = atomic64_read(&leader->dropped_samples);
 
 	__output_copy(handle, values, n * sizeof(u64));
 
@@ -7401,6 +7411,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 			values[n++] = primary_event_id(sub);
 		if (read_format & PERF_FORMAT_LOST)
 			values[n++] = atomic64_read(&sub->lost_samples);
+		if (read_format & PERF_FORMAT_DROPPED)
+			values[n++] = atomic64_read(&sub->dropped_samples);
 
 		__output_copy(handle, values, n * sizeof(u64));
 	}
-- 
2.46.0.469.g59c65b2a67-goog