drm/i915: Only apply the jump to the "efficient RPS" frequency on startup

Currently we apply the jump to rpe if we are below it and the GPU needs
more power. For some GPUs, the rpe is 75% of the maximum range causing
us to dramatically overshoot low power applications *and* unable to
reach the low frequency that can most efficiently deliver their
workload.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170210150348.22146-3-chris@chris-wilson.co.ukReviewed-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>

drivers/gpu/drm/i915/i915_irq.c

@@ -1173,14 +1173,6 @@ static void gen6_pm_rps_work(struct work_struct *work)
 
 		if (new_delay >= dev_priv->rps.max_freq_softlimit)
 			adj = 0;
-		/*
-		 * For better performance, jump directly
-		 * to RPe if we're below it.
-		 */
-		if (new_delay < dev_priv->rps.efficient_freq - adj) {
-			new_delay = dev_priv->rps.efficient_freq;
-			adj = 0;
-		}
 	} else if (client_boost || any_waiters(dev_priv)) {
 		adj = 0;
 	} else if (pm_iir & GEN6_PM_RP_DOWN_TIMEOUT) {

drivers/gpu/drm/i915/intel_pm.c

@@ -5019,6 +5019,8 @@ void gen6_rps_busy(struct drm_i915_private *dev_priv)
 {
 	mutex_lock(&dev_priv->rps.hw_lock);
 	if (dev_priv->rps.enabled) {
+		u8 freq;
+
 		if (dev_priv->pm_rps_events & (GEN6_PM_RP_DOWN_EI_EXPIRED | GEN6_PM_RP_UP_EI_EXPIRED))
 			gen6_rps_reset_ei(dev_priv);
 		I915_WRITE(GEN6_PMINTRMSK,
@@ -5026,9 +5028,14 @@ void gen6_rps_busy(struct drm_i915_private *dev_priv)
 
 		gen6_enable_rps_interrupts(dev_priv);
 
-		/* Ensure we start at the user's desired frequency */
+		/* Use the user's desired frequency as a guide, but for better
+		 * performance, jump directly to RPe as our starting frequency.
+		 */
+		freq = max(dev_priv->rps.cur_freq,
+			   dev_priv->rps.efficient_freq);
+
 		if (intel_set_rps(dev_priv,
-				  clamp(dev_priv->rps.cur_freq,
+				  clamp(freq,
 					dev_priv->rps.min_freq_softlimit,
 					dev_priv->rps.max_freq_softlimit)))
 			DRM_DEBUG_DRIVER("Failed to set idle frequency\n");