Re: [PATCH v2] drm/i915/selftests: Refactor RC6 power measurement and error handling

["Nilawar, Badal" <badal.nilawar@intel.com>]

On 04-03-2025 18:08, sk.anirban@intel.com wrote:
> From: Sk Anirban <sk.anirban@intel.com>
>
> Refactor power measurement logic to store and compare energy values.
> Introduce a threshold check to ensure the GPU enters RC6 properly.
>
> v2:
>    - Improved commit message (Badal)
>
> Signed-off-by: Sk Anirban <sk.anirban@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/selftest_rc6.c | 61 +++++++++++++++++---------
>   1 file changed, 40 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/selftest_rc6.c b/drivers/gpu/drm/i915/gt/selftest_rc6.c
> index 908483ab0bc8..30bc2ff040ce 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_rc6.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_rc6.c
> @@ -33,15 +33,20 @@ int live_rc6_manual(void *arg)
>   {
>   	struct intel_gt *gt = arg;
>   	struct intel_rc6 *rc6 = &gt->rc6;
> -	u64 rc0_power, rc6_power;
> +	struct intel_rps *rps = &gt->rps;
>   	intel_wakeref_t wakeref;
> +	u64 sleep_time = 1000;
> +	u32 rc0_freq = 0;
> +	u32 rc6_freq = 0;
> +	u64 rc0_power[3];
> +	u64 rc6_power[3];
>   	bool has_power;
> +	u64 threshold;
>   	ktime_t dt;
>   	u64 res[2];
>   	int err = 0;
> -	u32 rc0_freq = 0;
> -	u32 rc6_freq = 0;
> -	struct intel_rps *rps = &gt->rps;
> +	u64 diff;
> +
>   
>   	/*
>   	 * Our claim is that we can "encourage" the GPU to enter rc6 at will.
> @@ -65,9 +70,9 @@ int live_rc6_manual(void *arg)
>   	res[0] = rc6_residency(rc6);
>   
>   	dt = ktime_get();
> -	rc0_power = librapl_energy_uJ();
> -	msleep(1000);
> -	rc0_power = librapl_energy_uJ() - rc0_power;
> +	rc0_power[0] = librapl_energy_uJ();
> +	msleep(sleep_time);
> +	rc0_power[1] = librapl_energy_uJ() - rc0_power[0];
>   	dt = ktime_sub(ktime_get(), dt);
>   	res[1] = rc6_residency(rc6);
>   	rc0_freq = intel_rps_read_actual_frequency_fw(rps);
> @@ -79,11 +84,12 @@ int live_rc6_manual(void *arg)
>   	}
>   
>   	if (has_power) {
> -		rc0_power = div64_u64(NSEC_PER_SEC * rc0_power,
> -				      ktime_to_ns(dt));
> -		if (!rc0_power) {
> +		rc0_power[2] = div64_u64(NSEC_PER_SEC * rc0_power[1],
> +					 ktime_to_ns(dt));
> +
> +		if (!rc0_power[2]) {
>   			if (rc0_freq)
> -				pr_debug("No power measured while in RC0! GPU Freq: %u in RC0\n",
> +				pr_debug("No power measured while in RC0! GPU Freq: %uMHz in RC0\n",
>   					 rc0_freq);
>   			else
>   				pr_err("No power and freq measured while in RC0\n");
> @@ -98,10 +104,10 @@ int live_rc6_manual(void *arg)
>   	res[0] = rc6_residency(rc6);
>   	intel_uncore_forcewake_flush(rc6_to_uncore(rc6), FORCEWAKE_ALL);
>   	dt = ktime_get();
> -	rc6_power = librapl_energy_uJ();
> -	msleep(1000);
> +	rc6_power[0] = librapl_energy_uJ();
> +	msleep(sleep_time);
>   	rc6_freq = intel_rps_read_actual_frequency_fw(rps);
> -	rc6_power = librapl_energy_uJ() - rc6_power;
> +	rc6_power[1] = librapl_energy_uJ() - rc6_power[0];
>   	dt = ktime_sub(ktime_get(), dt);
>   	res[1] = rc6_residency(rc6);
>   	if (res[1] == res[0]) {
> @@ -112,14 +118,27 @@ int live_rc6_manual(void *arg)
>   		err = -EINVAL;
>   	}
>   
> +	diff = res[1] - res[0];
> +	threshold = (9 * NSEC_PER_MSEC * sleep_time) / 10;
> +	if (diff < threshold) {
> +		pr_err("Did not enter RC6 properly, RC6 start residency=%lluns, RC6 end residency=%lluns\n",
> +		       res[0], res[1]);

There is possibility of Residency could be slightly less than threshold, 
in that case it will end up throwing error.
Lets remove this check and error message from here and print residency, 
threshold in final error message.

> +		err = -EINVAL;
> +	}
> +
>   	if (has_power) {
> -		rc6_power = div64_u64(NSEC_PER_SEC * rc6_power,
> -				      ktime_to_ns(dt));
> -		pr_info("GPU consumed %llduW in RC0 and %llduW in RC6\n",
> -			rc0_power, rc6_power);
> -		if (2 * rc6_power > rc0_power) {
> -			pr_err("GPU leaked energy while in RC6! GPU Freq: %u in RC6 and %u in RC0\n",
> -			       rc6_freq, rc0_freq);
> +		rc6_power[2] = div64_u64(NSEC_PER_SEC * rc6_power[1],
> +					 ktime_to_ns(dt));
> +		pr_info("GPU consumed %lluuW in RC0 and %lluuW in RC6\n",
> +			rc0_power[2], rc6_power[2]);
> +
> +		if (2 * rc6_power[2] > rc0_power[2]) {
> +			pr_err("GPU leaked energy while in RC6!\n"
> +			       "GPU Freq: %uMHz in RC6 and %uMHz in RC0\n"
> +			       "RC0 energy before & after sleep respectively: %lluuJ %lluuJ\n"
> +			       "RC6 energy before & after sleep respectively: %lluuJ %lluuJ\n",
> +			       rc6_freq, rc0_freq, rc0_power[0], rc0_power[1],
> +			       rc6_power[0], rc6_power[1]);

As mentioned above add residency and threshold sleep time here.

Regards,
Badal

>   			err = -EINVAL;
>   			goto out_unlock;
>   		}