[LTP] [PATCH] perf_event_open02: set process as RT during Setup stage

[LTP] [PATCH] perf_event_open02: set process as RT during Setup stage

[Edward Liaw via ltp]

From: "kuan-ying.zhu" <kuan-ying.zhu@mediatek.com>

Move the action of set the task RT from the Verify stage to the Setup
stage. Avoid potential risks of task migration due to scheduler policy.

Signed-off-by: kuan-ying.zhu <kuan-ying.zhu@mediatek.com>
Signed-off-by: Edward Liaw <edliaw@google.com>
---
 .../syscalls/perf_event_open/perf_event_open02.c    | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/testcases/kernel/syscalls/perf_event_open/perf_event_open02.c b/testcases/kernel/syscalls/perf_event_open/perf_event_open02.c
index 7306ecf51..7b3305a52 100644
--- a/testcases/kernel/syscalls/perf_event_open/perf_event_open02.c
+++ b/testcases/kernel/syscalls/perf_event_open/perf_event_open02.c
@@ -198,6 +198,12 @@ static void setup(void)
 {
 	int i;
 	struct perf_event_attr tsk_event, hw_event;
+	struct sched_param sparam = {.sched_priority = 1};
+
+	if (sched_setscheduler(0, SCHED_FIFO, &sparam)) {
+		tst_brk(TBROK | TERRNO,
+			"sched_setscheduler(0, SCHED_FIFO, ...) failed");
+	}
 
 	for (i = 0; i < MAX_CTRS; i++) {
 		hwfd[i] = -1;
@@ -271,12 +277,7 @@ static void verify(void)
 	unsigned long long vtsum = 0, vhsum = 0;
 	int i;
 	double ratio;
-	struct sched_param sparam = {.sched_priority = 1};
-
-	if (sched_setscheduler(0, SCHED_FIFO, &sparam)) {
-		tst_brk(TBROK | TERRNO,
-			"sched_setscheduler(0, SCHED_FIFO, ...) failed");
-	}
+	struct sched_param sparam = {.sched_priority = 0};
 
 	all_counters_set(PR_TASK_PERF_EVENTS_ENABLE);
 	do_work(8);
-- 
2.48.1.711.g2feabab25a-goog


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Re: [LTP] [PATCH] perf_event_open02: set process as RT during Setup stage

[Cyril Hrubis]

Hi!
> Move the action of set the task RT from the Verify stage to the Setup
> stage. Avoid potential risks of task migration due to scheduler policy.

What exactly goes wrong if we switch to the realtime policy later? I
see that we do bench_work(500) at the start of the setup. That may mean
that we may get different estimate on how many loops we do per second,
but that would only mean that the test would run for shorter time.

We also do bind_to_current_cpu() just after that, the task shouldn't be
migrated after that.

The actual change looks reasonable, however the patch description should
tell why we need to do this change.

-- 
Cyril Hrubis
chrubis@suse.cz

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[LTP] 回覆: [PATCH] perf_event_open02: set process as RT during Setup stage

[Kuan-ying Zhu (朱冠穎) via ltp]

Hi,

Because in mobile products, power consumption requirements may cause the CPU to enter a temporary isolation state (CPU is active but tasks are not assigned) to save power. At this time, task affinity may fail. Therefore, to avoid testing errors caused by power-saving features related to this issue in embedded devices, this suggestion is proposed.

Kuan-ying.Zhu
Kuan-ying.Zhu@mediatek.com

________________________________
寄件者: Cyril Hrubis
已傳送: 星期二, 2025 年 3 月 18 日 下午 07:19
收件者: Edward Liaw
副本: ltp@lists.linux.it; Kuan-ying Zhu (朱冠穎); kernel-team@android.com
主旨: Re: [LTP] [PATCH] perf_event_open02: set process as RT during Setup stage


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Hi!
> Move the action of set the task RT from the Verify stage to the Setup
> stage. Avoid potential risks of task migration due to scheduler policy.

What exactly goes wrong if we switch to the realtime policy later? I
see that we do bench_work(500) at the start of the setup. That may mean
that we may get different estimate on how many loops we do per second,
but that would only mean that the test would run for shorter time.

We also do bind_to_current_cpu() just after that, the task shouldn't be
migrated after that.

The actual change looks reasonable, however the patch description should
tell why we need to do this change.

--
Cyril Hrubis
chrubis@suse.cz

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp