[Intel-gfx] [PATCH] drm/i915/pmu: Match frequencies reported by PMU and sysfs

[Ashutosh Dixit]

PMU and sysfs use different wakeref's to "interpret" zero freq. Sysfs uses
runtime PM wakeref (see intel_rps_read_punit_req and
intel_rps_read_actual_frequency). PMU uses the GT parked/unparked
wakeref. In general the GT wakeref is held for less time that the runtime
PM wakeref which causes PMU to report a lower average freq than the average
freq obtained from sampling sysfs.

To resolve this, use the same freq functions (and wakeref's) in PMU as
those used in sysfs.

Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/7025
Reported-by: Ashwin Kumar Kulkarni <ashwin.kumar.kulkarni at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/i915/i915_pmu.c | 27 ++-------------------------
 1 file changed, 2 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 958b37123bf1..eda03f264792 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -371,37 +371,16 @@ static void
 frequency_sample(struct intel_gt *gt, unsigned int period_ns)
 {
 	struct drm_i915_private *i915 = gt->i915;
-	struct intel_uncore *uncore = gt->uncore;
 	struct i915_pmu *pmu = &i915->pmu;
 	struct intel_rps *rps = &gt->rps;
 
 	if (!frequency_sampling_enabled(pmu))
 		return;
 
-	/* Report 0/0 (actual/requested) frequency while parked. */
-	if (!intel_gt_pm_get_if_awake(gt))
-		return;
-
 	if (pmu->enable & config_mask(I915_PMU_ACTUAL_FREQUENCY)) {
-		u32 val;
-
-		/*
-		 * We take a quick peek here without using forcewake
-		 * so that we don't perturb the system under observation
-		 * (forcewake => !rc6 => increased power use). We expect
-		 * that if the read fails because it is outside of the
-		 * mmio power well, then it will return 0 -- in which
-		 * case we assume the system is running at the intended
-		 * frequency. Fortunately, the read should rarely fail!
-		 */
-		val = intel_uncore_read_fw(uncore, GEN6_RPSTAT1);
-		if (val)
-			val = intel_rps_get_cagf(rps, val);
-		else
-			val = rps->cur_freq;
-
 		add_sample_mult(&pmu->sample[__I915_SAMPLE_FREQ_ACT],
-				intel_gpu_freq(rps, val), period_ns / 1000);
+				intel_rps_read_actual_frequency(rps),
+				period_ns / 1000);
 	}
 
 	if (pmu->enable & config_mask(I915_PMU_REQUESTED_FREQUENCY)) {
@@ -409,8 +388,6 @@ frequency_sample(struct intel_gt *gt, unsigned int period_ns)
 				intel_rps_get_requested_frequency(rps),
 				period_ns / 1000);
 	}
-
-	intel_gt_pm_put_async(gt);
 }
 
 static enum hrtimer_restart i915_sample(struct hrtimer *hrtimer)
-- 
2.34.1