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Message-ID:
<GV1PR08MB105210711A8786F45290F88D3FBD82@GV1PR08MB10521.eurprd08.prod.outlook.com>
Date: Thu, 20 Mar 2025 08:24:09 +0000
From: Yeo Reum Yun <YeoReum.Yun@....com>
To: "mingo@...nel.org" <mingo@...nel.org>, "peterz@...radead.org"
<peterz@...radead.org>, "acme@...nel.org" <acme@...nel.org>,
"namhyung@...nel.org" <namhyung@...nel.org>, Mark Rutland
<Mark.Rutland@....com>, "alexander.shishkin@...ux.intel.com"
<alexander.shishkin@...ux.intel.com>, "jolsa@...nel.org" <jolsa@...nel.org>,
"irogers@...gle.com" <irogers@...gle.com>, "adrian.hunter@...el.com"
<adrian.hunter@...el.com>, "kan.liang@...ux.intel.com"
<kan.liang@...ux.intel.com>, Leo Yan <Leo.Yan@....com>,
"james.clark@...aro.org" <james.clark@...aro.org>
CC: "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] events/core: fix acoount failure for event's
child_total_enable_time at task exit
Gentle ping in care of forgotten..
________________________________________
From: Yeoreum Yun <yeoreum.yun@....com>
Sent: 06 March 2025 12:33
To: mingo@...nel.org; peterz@...radead.org; acme@...nel.org; namhyung@...nel.org; Mark Rutland; alexander.shishkin@...ux.intel.com; jolsa@...nel.org; irogers@...gle.com; adrian.hunter@...el.com; kan.liang@...ux.intel.com; Leo Yan; james.clark@...aro.org
Cc: linux-perf-users@...r.kernel.org; linux-kernel@...r.kernel.org; Yeo Reum Yun
Subject: [PATCH v4] events/core: fix acoount failure for event's child_total_enable_time at task exit
The perf core code fails to account for total_enable_time of event
when its state is inactive.
Here is the error case for failure to account for total_enable_time for
core event:
sudo ./perf stat -vvv -e armv8_pmuv3_0/event=0x08/ -e armv8_pmuv3_1/event=0x08/ -- stress-ng --pthread=2 -t 2s
...
/*
* three number represetns each
* scaled count / total_enable_time / total_total_running_time
*/
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%)
Since above two events are belong to the same task context and
mutually-exclusive per cpu (they couldn't be active at the same time on the same cpu),
the total_enable_time should be the same (marked with ^^^^^^^^^^^)
and the summation of ratio should be 100%.
This account failure of total_enable_time because of
account failure of child_total_enable_time of child event when
child task exit.
Below table explains how the child_total_enable_time is failed to account at
exiting child task which switch cpus as time passes by (CPU0 -> CPU1 -> CPU0)
- in means sched_in.
- out means sched_out.
- exit means at the exit of child task.
NOTE: the value is before calling list_del_event(). which mean
the value at exit column will be added at parent event's
child_total_enable_time when child task exit.
- ctx is the child_task_ctx,
- e0 is the child_event which set with cpu == -1 and opened with pmu0 only
added in CPU0,
- e1 is the child_event which set with cpu == -1 and opened with pmu1 only
added in CPU1,
- e0 and e1 belongs to same child_task_ctx.
CPU0 (run t1) CPU1 (run t2) CPU0 (run t3)
| in | out | | in | out | | in | 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 *| | t1 | t1 + t3 |
------------------------------------------------------------------------------
e1->ena | 0 | 0 *| | t1 | t1 + t2 | | t1 + t2 | t1 + t2 X|
------------------------------------------------------------------------------
e1->run | 0 | 0 *| | 0 | t2 | | t2 | t2 X|
------------------------------------------------------------------------------
The value marked with * means it doesn't updates since event->state was
INACTIVE.
Please see the last CPU0's column with exit (marked with X).
Since e1's state is INACTIVE its total_enable_time doesn't update
and it remains with former value without accounting t3 time.
In this situation, at __perf_remove_from_context() while exit child_task,
sync_child_event() where adds child_event's total_enable_time to
parent event's child_total_enable_time in perf_child_detach() is called
before list_del_event() in which event time is updated by setting
the event state as OFF.
That means child_total_enable_time is added with missing
amount of last enable time -- t3.
In case of parent event's total_enable_time is updated properly in
list_del_event() when the task exit.
However, the child_total_enable_time is missed when child_task exited,
the perf prints error amount of enable_time (which is summation of
total_enable_time + child_total_enable_time).
To address this, update event state via perf_event_state() in
__perf_remove_from_context() and call it before perf_child_detach()
where parent's total_enable_time is updated.
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 10s
...
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>
Suggsted-by: Peter Zijlstra <peterz@...radead.org>
---
kernel/events/core.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6364319e2f88..058533a50493 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2407,6 +2407,7 @@ ctx_time_update_event(struct perf_event_context *ctx, struct perf_event *event)
#define DETACH_GROUP 0x01UL
#define DETACH_CHILD 0x02UL
#define DETACH_DEAD 0x04UL
+#define DETACH_EXIT 0x08UL
/*
* Cross CPU call to remove a performance event
@@ -2421,6 +2422,7 @@ __perf_remove_from_context(struct perf_event *event,
void *info)
{
struct perf_event_pmu_context *pmu_ctx = event->pmu_ctx;
+ enum perf_event_state state = PERF_EVENT_STATE_OFF;
unsigned long flags = (unsigned long)info;
ctx_time_update(cpuctx, ctx);
@@ -2429,16 +2431,19 @@ __perf_remove_from_context(struct perf_event *event,
* Ensure event_sched_out() switches to OFF, at the very least
* this avoids raising perf_pending_task() at this time.
*/
- if (flags & DETACH_DEAD)
+ if (flags & DETACH_EXIT)
+ state = PERF_EVENT_STATE_EXIT;
+ if (flags & DETACH_DEAD) {
event->pending_disable = 1;
+ state = PERF_EVENT_STATE_DEAD;
+ }
event_sched_out(event, ctx);
+ perf_event_set_state(event, min(event->state, state));
if (flags & DETACH_GROUP)
perf_group_detach(event);
if (flags & DETACH_CHILD)
perf_child_detach(event);
list_del_event(event, ctx);
- if (flags & DETACH_DEAD)
- event->state = PERF_EVENT_STATE_DEAD;
if (!pmu_ctx->nr_events) {
pmu_ctx->rotate_necessary = 0;
@@ -13424,12 +13429,7 @@ perf_event_exit_event(struct perf_event *event, struct perf_event_context *ctx)
mutex_lock(&parent_event->child_mutex);
}
- perf_remove_from_context(event, detach_flags);
-
- raw_spin_lock_irq(&ctx->lock);
- if (event->state > PERF_EVENT_STATE_EXIT)
- perf_event_set_state(event, PERF_EVENT_STATE_EXIT);
- raw_spin_unlock_irq(&ctx->lock);
+ perf_remove_from_context(event, detach_flags | DETACH_EXIT);
/*
* Child events can be freed.
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
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