[LTP] [PATCH] controllers/cpuacct: Dynamically adjust cpuacct_task execution time

[Wake Liu]

The test helper cpuacct_task currently runs for 10ms (virtual time)
before exiting. On some systems (e.g. fast virtual machines or under
heavy load), this short duration can lead to 0 usage being recorded in
cpuacct.usage cgroup file due to timing resolution or scheduling delay,
especially when running small configurations like cpuacct_1_1.

However, unconditionally increasing the duration for all runs (e.g. to
100ms) would cause large stress tests like cpuacct_100_100 (which runs
10,000 tasks) to timeout on systems with few CPUs.

Resolve this by:
1. Modifying cpuacct_task to accept an optional duration argument.
2. Modifying cpuacct.sh to calculate the duration dynamically based on
   nbprocess, ensuring each subgroup gets at least 100ms of aggregate
   CPU time, while clamping the per-process duration to a minimum of
   10ms to avoid timeouts in large stress tests.

Signed-off-by: Wake Liu <wakel@google.com>
---
 .../kernel/controllers/cpuacct/cpuacct.sh     |  7 ++++++-
 .../kernel/controllers/cpuacct/cpuacct_task.c | 20 ++++++++++++++++---
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/testcases/kernel/controllers/cpuacct/cpuacct.sh b/testcases/kernel/controllers/cpuacct/cpuacct.sh
index 97a395cd5..efabe6cab 100755
--- a/testcases/kernel/controllers/cpuacct/cpuacct.sh
+++ b/testcases/kernel/controllers/cpuacct/cpuacct.sh
@@ -139,10 +139,15 @@ do_test()
 {
 	tst_res TINFO "Creating $max subgroups each with $nbprocess processes"
 
+	local duration=$((100000 / nbprocess))
+	if [ $duration -lt 10000 ]; then
+		duration=10000
+	fi
+
 	# create and attach process to subgroups
 	for i in `seq 1 $max`; do
 		for j in `seq 1 $nbprocess`; do
-			cpuacct_task $testpath/subgroup_$i/tasks &
+			cpuacct_task $testpath/subgroup_$i/tasks $duration &
 			echo $! >> task_pids
 		done
 	done
diff --git a/testcases/kernel/controllers/cpuacct/cpuacct_task.c b/testcases/kernel/controllers/cpuacct/cpuacct_task.c
index 677d6d401..caeecf064 100644
--- a/testcases/kernel/controllers/cpuacct/cpuacct_task.c
+++ b/testcases/kernel/controllers/cpuacct/cpuacct_task.c
@@ -38,12 +38,21 @@ int main(int argc, char **argv)
 {
 	FILE *f;
 	struct sigaction sa;
+	int duration_us = 10000;
 
-	if (argc != 2) {
-		fprintf(stderr, "Usage: %s /cgroup/.../tasks\n", argv[0]);
+	if (argc < 2 || argc > 3) {
+		fprintf(stderr, "Usage: %s /cgroup/.../tasks [duration_us]\n", argv[0]);
 		return 1;
 	}
 
+	if (argc == 3) {
+		duration_us = atoi(argv[2]);
+		if (duration_us <= 0) {
+			fprintf(stderr, "Invalid duration: %s\n", argv[2]);
+			return 1;
+		}
+	}
+
 	f = fopen(argv[1], "a");
 	if (!f) {
 		perror("fopen failed");
@@ -62,7 +71,12 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	struct itimerval it = {.it_value = {.tv_sec = 0, .tv_usec = 10000}};
+	struct itimerval it = {
+		.it_value = {
+			.tv_sec = duration_us / 1000000,
+			.tv_usec = duration_us % 1000000
+		}
+	};
 
 	setitimer(ITIMER_VIRTUAL, &it, NULL);
 	for (;;);
-- 
2.55.0.654.g21b8a5bc05-goog