[i-g-t 1/2] tests/kms_vrr: Enhance flip accuracy measurement

[Golani, Mitulkumar Ajitkumar]

> -----Original Message-----
> From: Modem, Bhanuprakash <bhanuprakash.modem at intel.com>
> Sent: Wednesday, January 17, 2024 12:04 PM
> To: igt-dev at lists.freedesktop.org
> Cc: Modem, Bhanuprakash <bhanuprakash.modem at intel.com>; Golani,
> Mitulkumar Ajitkumar <mitulkumar.ajitkumar.golani at intel.com>
> Subject: [i-g-t 1/2] tests/kms_vrr: Enhance flip accuracy measurement
> 
> The threshold of ~50us, which is roughly the difference between 144Hz &
> 143Hz, to be too high for high refresh rate panels (like
> 60-360Hz) and too low for low refresh rate panels (like 40-60Hz) when
> measuring flip accuracy.
> 
> Revise the threshold to allow for a deviation of approximately
> (+/-) 1 Hz will improve the accuracy of flip measurements across a wider
> range of panel refresh rates.
> 
> Cc: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>
> Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem at intel.com>
> ---
>  tests/kms_vrr.c | 27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/tests/kms_vrr.c b/tests/kms_vrr.c index 71fc36162..44bc3480d
> 100644
> --- a/tests/kms_vrr.c
> +++ b/tests/kms_vrr.c
> @@ -339,10 +339,23 @@ static uint32_t
>  flip_and_measure(data_t *data, igt_output_t *output, enum pipe pipe,
>  		 uint64_t rate_ns, uint64_t duration_ns)  {
> -	uint64_t start_ns, last_event_ns, target_ns;
> +	uint64_t start_ns, last_event_ns, target_ns, exp_rate_ns;
>  	uint32_t total_flip = 0, total_pass = 0;
>  	bool front = false;
>  	vtest_ns_t vtest_ns = get_test_rate_ns(data->range);
> +	uint64_t threshold_hi, threshold_lo;
> +
> +	if ((rate_ns <= vtest_ns.min) && (rate_ns >= vtest_ns.max))
> +		exp_rate_ns = rate_ns;
> +	else
> +		exp_rate_ns = vtest_ns.max;
> +
> +	/* Allow ~1 Hz deviation for different reasons causing delay. */
> +	threshold_hi = NSECS_PER_SEC / (((float)NSECS_PER_SEC /
> exp_rate_ns) + 1);
> +	threshold_lo = NSECS_PER_SEC / (((float)NSECS_PER_SEC /
> exp_rate_ns) -
> +1);
> +
> +	igt_info("Requested rate: %"PRIu64" ns, Expected rate between:
> %"PRIu64" ns to %"PRIu64" ns\n",
> +			rate_ns, threshold_hi, threshold_lo);
> 
>  	/* Align with the flip completion event to speed up convergence. */
>  	do_flip(data, &data->fb0);
> @@ -369,18 +382,10 @@ flip_and_measure(data_t *data, igt_output_t
> *output, enum pipe pipe,
>  		/*
>  		 * Check if the difference between the two flip timestamps
>  		 * was within the required threshold from the expected rate.
> -		 *
> -		 * A ~50us threshold is arbitrary, but it's roughly the
> -		 * difference between 144Hz and 143Hz which should give
> this
> -		 * enough accuracy for most use cases.
>  		 */
> -		if ((rate_ns <= vtest_ns.min) && (rate_ns >= vtest_ns.max))
> -			diff_ns = rate_ns;
> -		else
> -			diff_ns = vtest_ns.max;
> -		diff_ns -= event_ns - last_event_ns;
> +		diff_ns = event_ns - last_event_ns;
> 
> -		if (llabs(diff_ns) < 50000ll)
> +		if (llabs(diff_ns) < threshold_lo && llabs(diff_ns) >
> threshold_hi)

Changes LGTM
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>

>  			total_pass += 1;
> 
>  		last_event_ns = event_ns;
> --
> 2.40.0