[PATCH 41/76] drm/i915: Reduce RPS update frequency on Valleyview/Cherryview

Chris Wilson chris at chris-wilson.co.uk
Sat Jun 2 09:37:44 UTC 2018


Valleyview and Cherryview update the GPU frequency via the punit, which
is very expensive as we have to ensure the cores do not sleep during the
comms. If we perform frequent RPS evaluations, the frequent punit
requests cause measurable system overhead for little benefit, so
increase the evaluation intervals to reduce the number of times we try
and change frequency.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_pm.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 02cc7a6a34d6..d4c2b67e44de 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6342,6 +6342,19 @@ static void gen6_set_rps_thresholds(struct drm_i915_private *dev_priv, u8 val)
 		break;
 	}
 
+	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
+		/*
+		 * Baytrail and Braswell control the gpu frequency via the
+		 * punit, which is very slow and expensive to communicate with,
+		 * as we synchronously force the package to C0. If we try and
+		 * update the gpufreq too often we cause measurable system
+		 * load for little benefit (effectively stealing CPU time for
+		 * the GPU, negatively impacting overall throughput).
+		 */
+		ei_up <<= 2;
+		ei_down <<= 2;
+	}
+
 	/* When byt can survive without system hang with dynamic
 	 * sw freq adjustments, this restriction can be lifted.
 	 */
-- 
2.17.1



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