[LTP] [PATCH v2] sched: starvation: Autocallibrate the timeout

[Petr Vorel]

Hi Cyril,

> Instead of hardcoding the values we attempt to measure the CPU speed and
> set the timeout accordingly. Given that the difference in the duration
> of the test when the kernel is buggy is about 30x we do not have to have
> a precise callibration, just very rough estimate if we are running on a
> server or small ARM board would suffice.

> So we attempt to measure how long does a bussy loop take and base the
s/bussy/busy/

> default timeout on that. On x86_64 CPUs the resulting timeout is about
> double of the value of the actual test runtime and works fine, but we
> need to make sure that the coeficient we divide the result from
> callibrate works for small boards too. So please run the test on as many
> machines as you can and report if we need to make the dividor smaller or
> not.

This looks much better: ppc64le has Timeout per run is 0h 00m 30s (1m 10s
runtime), others (x68_64, s390x, aarch64) have ~ 1 min or less.

Tested-by: Petr Vorel <pvorel@suse.cz>

...
> +static int callibrate(void)
> +{
> +	int i;
> +	struct timespec start, stop;
> +	long long diff;
> +
> +	for (i = 0; i < CALLIBRATE_LOOPS; i++) {
> +		__asm__ __volatile__ ("" : "+g" (i) : :);
> +	}
> +
> +	SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &start);
> +
> +	for (i = 0; i < CALLIBRATE_LOOPS; i++) {
> +		__asm__ __volatile__ ("" : "+g" (i) : :);
> +	}
> +
> +	SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &stop);
> +
> +	diff = tst_timespec_diff_us(stop, start);
> +
> +	tst_res(TINFO, "CPU did %i loops in %llius", CALLIBRATE_LOOPS, diff);
> +
> +	return diff;
> +}

>  static int wait_for_pid(pid_t pid)
>  {
> @@ -59,8 +88,11 @@ static void setup(void)
>  	if (tst_parse_long(str_loop, &loop, 1, LONG_MAX))
>  		tst_brk(TBROK, "Invalid number of loop number '%s'", str_loop);

> -	if (tst_parse_int(str_timeout, &timeout, 1, INT_MAX))
> +	if (tst_parse_int(str_timeout, &timeout, 1, INT_MAX)) {
nit: {} brackets are not needed.

Reviewed-by: Petr Vorel <pvorel@suse.cz>

Kind regards,
Petr

>  		tst_brk(TBROK, "Invalid number of timeout '%s'", str_timeout);
> +	} else {
> +		timeout = callibrate() / 1000;
> +	}

>  	tst_set_max_runtime(timeout);
>  }