Re: [PATCH v3 2/2] cgroup/rstat: Selftests for niced CPU statistics

On Mon, Sep 23, 2024 at 07:20:06AM GMT, Joshua Hahn joshua.hahnjy@gmail.com wrote:

+/*

• • Creates a nice process that consumes CPU and checks that the elapsed
• • usertime in the cgroup is close to the expected time.
• */

+static int test_cpucg_nice(const char *root) +{

• int ret = KSFT_FAIL;
• int status;
• long user_usec, nice_usec;
• long usage_seconds = 2;
• long expected_nice_usec = usage_seconds * USEC_PER_SEC;
• char *cpucg;
• pid_t pid;
• cpucg = cg_name(root, "cpucg_test");
• if (!cpucg)

• goto cleanup;
  

• if (cg_create(cpucg))

• goto cleanup;
  

• user_usec = cg_read_key_long(cpucg, "cpu.stat", "user_usec");
• nice_usec = cg_read_key_long(cpucg, "cpu.stat", "nice_usec");
• if (user_usec != 0 || nice_usec != 0)

• goto cleanup;
  

Can you please distinguish a check between non-zero nice_usec and non-existent nice_usec (KSFT_FAIL vs KSFT_SKIP)? So that the selftest is usable on older kernels too.

• /*

• * We fork here to create a new process that can be niced without
  

• * polluting the nice value of other selftests
  

• */
  

• pid = fork();
• if (pid < 0) {

• goto cleanup;
  

• } else if (pid == 0) {

• struct cpu_hog_func_param param = {
  

• 	.nprocs = 1,
  

• 	.ts = {
  

• 		.tv_sec = usage_seconds,
  

• 		.tv_nsec = 0,
  

• 	},
  

• 	.clock_type = CPU_HOG_CLOCK_PROCESS,
  

• };
  

• /* Try to keep niced CPU usage as constrained to hog_cpu as possible */
  

• nice(1);
  

• cg_run(cpucg, hog_cpus_timed, (void *)&param);
  

Notice that cg_run() does fork itself internally. So you can call hog_cpus_timed(cpucg, (void *)&param) directly, no need for the fork with cg_run(). (Alternatively substitute fork in this test with the fork in cg_run() but with extension of cpu_hog_func_params with the nice value.)

Thanks, Michal