[LTP] [PATCH v2] syscalls/prctl08: New test for prctl() with PR_{SET, GET}_TIMERSLACK

[Yang Xu]

> Hi!
>> +static struct tcase {
>> +	unsigned long setvalue;
>> +	unsigned long cmptime;
>> +} tcases[] = {
>> +	{1, 50000},
>> +	{70000, 120000},
>> +	{INT_MAX, 50000},
>> +};
>> +
>> +static int proc_flag = 1;
>> +
>> +static void check_proc_ns(char *message, unsigned long value)
>> +{
>> +	unsigned long proc_value;
>> +
>> +	SAFE_FILE_SCANF(PROC_NS_PATH, "%lu",&proc_value);
>> +	if (proc_value == value)
>> +		tst_res(TPASS, "%s %s  got %lu expectedly",
>> +				message, PROC_NS_PATH, proc_value);
>> +	else
>> +		tst_res(TFAIL, "%s %s expected %lu got %lu",
>> +				message, PROC_NS_PATH, value, proc_value);
>> +}
>> +
>> +static void check_get_timerslack(char *message, unsigned long value)
>> +{
>> +	TEST(prctl(PR_GET_TIMERSLACK));
>> +	if ((unsigned long)TST_RET == value)
>> +		tst_res(TPASS, "%s prctl(PR_GET_TIMERSLACK) got %lu expectedly",
>> +				message, value);
>> +	else
>> +		tst_res(TFAIL, "%s prctl(PR_GET_TIMERSLACK) expected %lu got %lu",
>> +				message, value, TST_RET);
>> +
>> +	if (proc_flag)
>> +		check_proc_ns(message, value);
>> +}
>> +
>> +static void verify_prctl(unsigned int n)
>> +{
>> +	struct tcase *tc =&tcases[n];
>> +	int pid;
>> +
>> +	struct timespec timereq = { .tv_sec = 0, .tv_nsec = 50000 };
>> +	struct timespec timecmp = { .tv_sec = 0, .tv_nsec = tc->cmptime};
>> +
>> +	TEST(prctl(PR_SET_TIMERSLACK, tc->setvalue));
>> +	if (TST_RET == -1) {
>> +		tst_res(TFAIL | TTERRNO, "prctl(PR_SET_TIMERSLACK, %lu) failed",
>> +				tc->setvalue);
>> +		return;
>> +	}
>> +	tst_res(TPASS, "prctl(PR_SET_TIMERSLACK, %lu) success", tc->setvalue);
>> +
>> +	pid = SAFE_FORK();
>> +	if (pid == 0) {
>> +		check_get_timerslack("child process", tc->setvalue);
>> +		/* A value of 0 means using default */
>> +		prctl(PR_SET_TIMERSLACK, 0);
> Why do we reset the slack before the measurements?
Hi Cyril

    I reset it because  I want to test whether default timer_slack in child process is the same as the current value
of the creating thread.

I also sent a patch about PR_SET_TIMERSLACK to man-page, as below:
https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=c14f79303f2885f7f4f4bf0d63922551b520a4b8



>> +		check_get_timerslack("After set 0, child process", tc->setvalue);
>> +
>> +		tst_timer_start(CLOCK_MONOTONIC);
>> +		TEST(nanosleep(&timereq, NULL));
>> +		tst_timer_stop();
>> +
>> +		if (tst_timespec_lt(tst_timer_elapsed(), timecmp))
>> +			tst_brk(TFAIL, "nanosleep() slept less than timecmp");
> I do not get what we are trying to assert here.
>
> As far as I understand it the timer slack is a way how to inform kernel
> that it's okay if the timers are slightly less precise. However the
> timer still can fire somewhere between sleep time and sleep time +
> slack, or even maybe later if the system is under load.
Yes. timer still can fire somewhere in [sleep, sleep+slack] range even later.

> BTW we do have a formula that tries to compute maximal time the timers
> should sleep based on timer slack in lib/tst_timer_test.c but even with
> that we have to take more samples and compute truncated mean because
> single short sleep may be delayed unless it's a RT kernel...
>
Yes . Agree. Single short sleep may be delayed and I will take more samples.

>> +		tst_res(TPASS, "nanosleep() slept more than timecmp, %llius",
>> +				tst_timer_elapsed_us());
>> +		exit(0);
>> +	}
>> +}
>> +
>> +static void setup(void)
>> +{
>> +	if (access(PROC_NS_PATH, F_OK) == -1) {
>> +		tst_res(TCONF, "proc doesn't support timerslack_ns interface");
>> +		proc_flag = 0;
>> +	}
>> +}
>> +
>> +static struct tst_test test = {
>> +	.setup = setup,
>> +	.test = verify_prctl,
>> +	.tcnt = ARRAY_SIZE(tcases),
>> +	.forks_child = 1,
>> +};
>> -- 
>> 2.18.1
>>
>>
>>
>>
>> -- 
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