[Intel-gfx] [PATCH 2/5] drm/i915: Expose idle delays to Kconfig

[Chris Wilson]

We want to expose the parameters for controlling how long it takes for
us to notice and park the GPU after a stream of requests in order to try
and tune the optimal power-efficiency vs latency of a mostly idle system.

v2: retire_work has two scheduling points, update them both

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/Kconfig.profile | 23 +++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem.c      |  8 +++++---
 drivers/gpu/drm/i915/i915_gem.h      | 13 +++++++++++++
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/Kconfig.profile b/drivers/gpu/drm/i915/Kconfig.profile
index 8a230eeb98df..63cb744d920d 100644
--- a/drivers/gpu/drm/i915/Kconfig.profile
+++ b/drivers/gpu/drm/i915/Kconfig.profile
@@ -24,3 +24,26 @@ config DRM_I915_SPIN_REQUEST_CS
 	  spin prior to sleeping again.
 
 	  May be 0 to disable spinning after being woken.
+
+config DRM_I915_GEM_RETIRE_DELAY
+	int
+	default 1000 # milliseconds
+	help
+	  We maintain a background job whose purpose is to keep cleaning up
+	  after userspace, and may be the first to spot an idle system. This
+	  parameter determines the interval between execution of the worker.
+
+	  To reduce the number of timer wakeups, large delays (of greater than
+	  a second) are rounded to the next walltime second to allow coalescing
+	  of multiple system timers into a single wakeup.
+
+config DRM_I915_GEM_PARK_DELAY
+	int
+	default 100 # milliseconds
+	help
+	  Before parking the engines and the GPU after the final request is
+	  retired, we may wait for a small delay to reduce the frequecy of
+	  having to park/unpark and so the latency in executing a new request.
+
+	  May be 0 to immediately start parking the engines after the last
+	  request.
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 460f256114f7..5b538a92631d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -192,7 +192,9 @@ void i915_gem_park(struct drm_i915_private *i915)
 		return;
 
 	/* Defer the actual call to __i915_gem_park() to prevent ping-pongs */
-	mod_delayed_work(i915->wq, &i915->gt.idle_work, msecs_to_jiffies(100));
+	mod_delayed_work(i915->wq,
+			 &i915->gt.idle_work,
+			 msecs_to_jiffies(CONFIG_DRM_I915_GEM_PARK_DELAY));
 }
 
 void i915_gem_unpark(struct drm_i915_private *i915)
@@ -236,7 +238,7 @@ void i915_gem_unpark(struct drm_i915_private *i915)
 
 	queue_delayed_work(i915->wq,
 			   &i915->gt.retire_work,
-			   round_jiffies_up_relative(HZ));
+			   i915_gem_retire_delay());
 }
 
 int
@@ -3466,7 +3468,7 @@ i915_gem_retire_work_handler(struct work_struct *work)
 	if (READ_ONCE(dev_priv->gt.awake))
 		queue_delayed_work(dev_priv->wq,
 				   &dev_priv->gt.retire_work,
-				   round_jiffies_up_relative(HZ));
+				   i915_gem_retire_delay());
 }
 
 static void shrink_caches(struct drm_i915_private *i915)
diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index e46592956872..c6b4971435dc 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -27,6 +27,8 @@
 
 #include <linux/bug.h>
 #include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/timer.h>
 
 struct drm_i915_private;
 
@@ -76,6 +78,17 @@ struct drm_i915_private;
 void i915_gem_park(struct drm_i915_private *i915);
 void i915_gem_unpark(struct drm_i915_private *i915);
 
+static inline unsigned long i915_gem_retire_delay(void)
+{
+	const unsigned long delay =
+		msecs_to_jiffies(CONFIG_DRM_I915_GEM_RETIRE_DELAY);
+
+	if (CONFIG_DRM_I915_GEM_RETIRE_DELAY >= 1000)
+		return round_jiffies_up_relative(delay);
+	else
+		return delay;
+}
+
 static inline void __tasklet_disable_sync_once(struct tasklet_struct *t)
 {
 	if (atomic_inc_return(&t->count) == 1)
-- 
2.18.0