linux-kernel - [PATCH 1/1] events/core: fix error run/enable ratio display

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Message-Id: <20241218084656.609764-1-yeoreum.yun@arm.com>
Date: Wed, 18 Dec 2024 08:46:56 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	amhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com,
	james.clark@...aro.org
Cc: linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	nd@....com,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH 1/1] events/core: fix error run/enable ratio display

when runs below command (with core pmu) sometime perf prints error
ratio for each perf.

sudo ./perf stat -vvv -e armv8_pmuv3_0/event=0x08/ -e armv8_pmuv3_1/event=0x08/ -- stress-ng --pthread=2 -t 2s
...
armv8_pmuv3_0/event=0x08/: -1: 1081702126 2289429840 2174835740
armv8_pmuv3_1/event=0x08/: -1: 794080238 1950025700 847648440
armv8_pmuv3_0/event=0x08/: 1138698008 2289429840 2174835740
armv8_pmuv3_1/event=0x08/: 1826791390 1950025700 847648440

 Performance counter stats for 'stress-ng --pthread=2 -t 2s':

     1,138,698,008      armv8_pmuv3_0/event=0x08/                                               (94.99%)
     1,826,791,390      armv8_pmuv3_1/event=0x08/                                               (43.47%)

This happens because of missing total_enable_time of inactivate event.
it's enabled time doesn't update at the event_sched_out() because state
isn't PERF_EVENT_STATE_ACTIVE but PERF_EVENT_STATE_INACTIVE.

For example, Suppose there're two events:
    e0: with pmu0 which supports only cpu0
    e1: with pmu1 which supports only cpu1.
then

               CPU0                  CPU1                     CPU0
          |  in | out |       | in | out     |       | in      | out (exit)   |
------------------------------------------------------------------------------
ctx->time |  0  | t1  |       | t1 | t1 + t2 |       | t1 + t2 | t1 + t2 + t3 |
------------------------------------------------------------------------------
e0->ena   |  0  | t1  |       | t1 | t1      |       | t1 + t2 | t1 + t2 + t3 |
------------------------------------------------------------------------------
e0->run   |  0  | t1  |       | t1 | t1 + t2 |       | t1 + t2 | t1 + t3      |
------------------------------------------------------------------------------
e1->ena   |  0  | 0   |       | t1 | t1 + t2 |       | t1 + t2 | t1 + t2      |
------------------------------------------------------------------------------
e1->run   |  0  | 0   |       | 0  | t2      |       | t1 + t2 | t2           |
------------------------------------------------------------------------------

at the CPU0, state of e1 is PERF_EVENT_STATE_INACTIVE since it doesn't
support on CPU0. So when event_sched_out() it failed to update its
total_enable_time and it makes error print of run/ena ratio.

To address this, update total_enable_time in event_sched_out() when event state
is PERF_EVENT_STATE_INACTIVE.

After this patch, this problem is gone like:

sudo ./perf stat -vvv -e armv8_pmuv3_0/event=0x08/ -e armv8_pmuv3_1/event=0x08/ -- stress-ng --pthread=2 -t 2s
...
armv8_pmuv3_0/event=0x08/: -1: 10484528214 32157963940 21898169000
armv8_pmuv3_1/event=0x08/: -1: 7155819373 32157963940 10259794940
armv8_pmuv3_0/event=0x08/: 15396770398 32157963940 21898169000
armv8_pmuv3_1/event=0x08/: 22428964974 32157963940 10259794940

 Performance counter stats for 'stress-ng --pthread=2 -t 10s':

    15,396,770,398      armv8_pmuv3_0/event=0x08/                                               (68.10%)
    22,428,964,974      armv8_pmuv3_1/event=0x08/                                               (31.90%)

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
 kernel/events/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 065f9188b44a..f40cca02636d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2311,6 +2311,11 @@ event_sched_out(struct perf_event *event, struct perf_event_context *ctx)
 	WARN_ON_ONCE(event->ctx != ctx);
 	lockdep_assert_held(&ctx->lock);
 
+	if (event->state == PERF_EVENT_STATE_INACTIVE) {
+		perf_event_update_time(event);
+		return ;
+	}
+
 	if (event->state != PERF_EVENT_STATE_ACTIVE)
 		return;
 
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}