[PATCH V4 2/5] perf: Extend perf_output_read

[kan.liang@linux.intel.com]

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

The event may have been updated in the PMU-specific implementation,
e.g., Intel PEBS counters snapshotting. The common code should not
read and overwrite the value.

The PERF_SAMPLE_READ in the data->sample_type can be used to detect
whether the PMU-specific value is available. If yes, avoid the
pmu->read() in the common code.

Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---
 kernel/events/core.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index aa3450bdc227..fcc55d0b5848 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7269,7 +7269,7 @@ static void perf_output_read_one(struct perf_output_handle *handle,
 
 static void perf_output_read_group(struct perf_output_handle *handle,
 			    struct perf_event *event,
-			    u64 enabled, u64 running)
+			    u64 enabled, u64 running, bool read)
 {
 	struct perf_event *leader = event->group_leader, *sub;
 	u64 read_format = event->attr.read_format;
@@ -7291,7 +7291,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
 		values[n++] = running;
 
-	if ((leader != event) &&
+	if ((leader != event) && read &&
 	    (leader->state == PERF_EVENT_STATE_ACTIVE))
 		leader->pmu->read(leader);
 
@@ -7306,7 +7306,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 	for_each_sibling_event(sub, leader) {
 		n = 0;
 
-		if ((sub != event) &&
+		if ((sub != event) && read &&
 		    (sub->state == PERF_EVENT_STATE_ACTIVE))
 			sub->pmu->read(sub);
 
@@ -7333,7 +7333,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
  * on another CPU, from interrupt/NMI context.
  */
 static void perf_output_read(struct perf_output_handle *handle,
-			     struct perf_event *event)
+			     struct perf_event *event,
+			     bool read)
 {
 	u64 enabled = 0, running = 0, now;
 	u64 read_format = event->attr.read_format;
@@ -7351,7 +7352,7 @@ static void perf_output_read(struct perf_output_handle *handle,
 		calc_timer_values(event, &now, &enabled, &running);
 
 	if (event->attr.read_format & PERF_FORMAT_GROUP)
-		perf_output_read_group(handle, event, enabled, running);
+		perf_output_read_group(handle, event, enabled, running, read);
 	else
 		perf_output_read_one(handle, event, enabled, running);
 }
@@ -7393,7 +7394,7 @@ void perf_output_sample(struct perf_output_handle *handle,
 		perf_output_put(handle, data->period);
 
 	if (sample_type & PERF_SAMPLE_READ)
-		perf_output_read(handle, event);
+		perf_output_read(handle, event, !(data->sample_flags & PERF_SAMPLE_READ));
 
 	if (sample_type & PERF_SAMPLE_CALLCHAIN) {
 		int size = 1;
@@ -7994,7 +7995,7 @@ perf_event_read_event(struct perf_event *event,
 		return;
 
 	perf_output_put(&handle, read_event);
-	perf_output_read(&handle, event);
+	perf_output_read(&handle, event, true);
 	perf_event__output_id_sample(event, &handle, &sample);
 
 	perf_output_end(&handle);
-- 
2.38.1