[igt-dev] [i-g-t] tests/kms_setmode: basic Improve accuracy with using of confidence interval

[Chris Wilson]

Quoting Anand Moon (2020-11-02 09:08:36)
> Using confidence interval formula accuracy is estimates approximately
> at 95% when {X} is the average of a sample of size n.
> Use this confidence interval formula as used in statistics
> to estimate the accuracy.
> 
> Signed-off-by: Anand Moon <anandx.ram.moon at intel.com>
> ---
> See below link.
> https://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule#Cumulative_distribution_function
> ---
>  tests/kms_setmode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tests/kms_setmode.c b/tests/kms_setmode.c
> index 92f3ead2..58814a13 100644
> --- a/tests/kms_setmode.c
> +++ b/tests/kms_setmode.c
> @@ -494,7 +494,7 @@ static void check_timings(int crtc_idx, const drmModeModeInfo *kmode)
>          * which depend on timing, giving the lowest acceptable MTBF of 5.6s
>          * for 60Hz sampling rate.
>          */
> -       accuracy = 3. * stddev;
> +       accuracy = 3. * stddev / sqrt(CALIBRATE_TS_STEPS);

Oops, yes, this should be standard error rather than deviation. Could you
add igt_stats_get_std_error() so we don't hardcode N?
-Chris