linux-kernel - [PATCH V5 3/4] perf: Extend perf_output

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Message-Id: <20241216204505.748363-3-kan.liang@linux.intel.com>
Date: Mon, 16 Dec 2024 12:45:04 -0800
From: kan.liang@...ux.intel.com
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	irogers@...gle.com,
	linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Cc: ak@...ux.intel.com,
	eranian@...gle.com,
	Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH V5 3/4] perf: Extend perf_output_read

From: Kan Liang <kan.liang@...ux.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@...ux.intel.com>
Reviewed-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---

No change from V4

The V4 can be found at
https://lore.kernel.org/lkml/20240731143835.771618-1-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 684d631e78da..e2045403521a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7422,7 +7422,7 @@ 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;
@@ -7445,7 +7445,7 @@ 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);
 
@@ -7460,7 +7460,7 @@ 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);
 
@@ -7491,7 +7491,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
  * all cores.
  */
 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;
@@ -7509,7 +7510,7 @@ 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);
 }
@@ -7551,7 +7552,7 @@ 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;
@@ -8195,7 +8196,7 @@ 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