[PATCH 4/4] drm/i915: Dampen RPS slow start

[Chris Wilson]

Currently, we note congestion for the slow start ramping up of RPS only
when we overshoot the target workload and have to reverse direction for
our reclocking. That is, if we have a period where the current GPU
frequency is enough to sustain the workload within our target
utilisation, we should not trigger any RPS EI interrupts, and then may
continue again with the previous last_adj after multiple periods causing
us to dramatically overreact. To prevent us not noticing a period where
the system is behaving correctly, we can schedule an extra interrupt
that will not be associated with either an up or down event causing to
reset last_adj back to zero, cancelling the slow start due to the
congestion.

v2: Separate up/down EI

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/i915_irq.c | 26 ++++++++++++++++++++------
 drivers/gpu/drm/i915/intel_pm.c | 14 ++++++++++----
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 8084e35b25c5..14359656f63a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1298,7 +1298,13 @@ static void gen6_pm_rps_work(struct work_struct *work)
 
 	mutex_lock(&dev_priv->pcu_lock);
 
-	pm_iir |= vlv_wa_c0_ei(dev_priv, pm_iir);
+	dev_priv->pm_rps_events &=
+		~(GEN6_PM_RP_DOWN_EI_EXPIRED | GEN6_PM_RP_UP_EI_EXPIRED);
+
+	if (IS_VALLEYVIEW(dev_priv)) {
+		dev_priv->pm_rps_events |= GEN6_PM_RP_UP_EI_EXPIRED;
+		pm_iir |= vlv_wa_c0_ei(dev_priv, pm_iir);
+	}
 
 	adj = rps->last_adj;
 	new_delay = rps->cur_freq;
@@ -1310,10 +1316,12 @@ static void gen6_pm_rps_work(struct work_struct *work)
 		new_delay = rps->boost_freq;
 		adj = 0;
 	} else if (pm_iir & GEN6_PM_RP_UP_THRESHOLD) {
-		if (adj > 0)
+		if (adj > 0) {
+			dev_priv->pm_rps_events |= GEN6_PM_RP_UP_EI_EXPIRED;
 			adj *= 2;
-		else /* CHV needs even encode values */
+		} else { /* CHV needs even encode values */
 			adj = IS_CHERRYVIEW(dev_priv) ? 2 : 1;
+		}
 
 		if (new_delay >= rps->max_freq_softlimit)
 			adj = 0;
@@ -1326,15 +1334,21 @@ static void gen6_pm_rps_work(struct work_struct *work)
 			new_delay = rps->min_freq_softlimit;
 		adj = 0;
 	} else if (pm_iir & GEN6_PM_RP_DOWN_THRESHOLD) {
-		if (adj < 0)
+		if (adj < 0) {
+			dev_priv->pm_rps_events |= GEN6_PM_RP_DOWN_EI_EXPIRED;
 			adj *= 2;
-		else /* CHV needs even encode values */
+		} else { /* CHV needs even encode values */
 			adj = IS_CHERRYVIEW(dev_priv) ? -2 : -1;
+		}
 
 		if (new_delay <= rps->min_freq_softlimit)
 			adj = 0;
-	} else { /* unknown event */
+	} else if (pm_iir & GEN6_PM_RP_UP_THRESHOLD && adj > 0) {
+		adj = 0;
+	} else if (pm_iir & GEN6_PM_RP_DOWN_THRESHOLD && adj < 0) {
 		adj = 0;
+	} else {
+		/* unknown event */
 	}
 
 	rps->last_adj = adj;
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index f90a3c7f1c40..d71a498ee3a1 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6397,10 +6397,16 @@ static u32 gen6_rps_pm_mask(struct drm_i915_private *dev_priv, u8 val)
 	u32 mask = 0;
 
 	/* We use UP_EI_EXPIRED interupts for both up/down in manual mode */
-	if (val > rps->min_freq_softlimit)
-		mask |= GEN6_PM_RP_UP_EI_EXPIRED | GEN6_PM_RP_DOWN_THRESHOLD | GEN6_PM_RP_DOWN_TIMEOUT;
-	if (val < rps->max_freq_softlimit)
-		mask |= GEN6_PM_RP_UP_EI_EXPIRED | GEN6_PM_RP_UP_THRESHOLD;
+	if (val > rps->min_freq_softlimit) {
+		mask |= (GEN6_PM_RP_UP_EI_EXPIRED |
+			 GEN6_PM_RP_DOWN_EI_EXPIRED |
+			 GEN6_PM_RP_DOWN_THRESHOLD |
+			 GEN6_PM_RP_DOWN_TIMEOUT);
+	}
+	if (val < rps->max_freq_softlimit) {
+		mask |= (GEN6_PM_RP_UP_EI_EXPIRED |
+			 GEN6_PM_RP_UP_THRESHOLD);
+	}
 
 	mask &= dev_priv->pm_rps_events;
 
-- 
2.18.0