[Intel-gfx] [PATCH v2 3/3] drm/i915: optimise intel_runtime_pm_{get, put}

[David Weinehall]

Benchmarking shows that on resume we spend quite a bit of time
just taking and dropping these references, leaving us two options;
either rewriting the code not to take these references more than
once, which would be a rather invasive change since the involved
functions are used from other places, or to optimise
intel_runtime_pm_{get,put}().  This patch does the latter.
Initial benchmarking indicate improvements of a couple
of milliseconds on resume.

Original patch by Chris, with slight fixes by me.

v2: Fix missing return value (Patchwork)
    Remove extra atomic_dec() (Chris)

Signed-off-by: David Weinehall <david.weinehall at linux.intel.com>
CC: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_runtime_pm.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 356c662ad453..831fde343d10 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -2632,6 +2632,9 @@ void intel_runtime_pm_get(struct drm_i915_private *dev_priv)
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	struct device *kdev = &pdev->dev;
 
+	if (atomic_inc_not_zero(&dev_priv->pm.wakeref_count))
+		return;
+
 	pm_runtime_get_sync(kdev);
 
 	atomic_inc(&dev_priv->pm.wakeref_count);
@@ -2653,6 +2656,9 @@ bool intel_runtime_pm_get_if_in_use(struct drm_i915_private *dev_priv)
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	struct device *kdev = &pdev->dev;
 
+	if (atomic_inc_not_zero(&dev_priv->pm.wakeref_count))
+		return true;
+
 	if (IS_ENABLED(CONFIG_PM)) {
 		int ret = pm_runtime_get_if_in_use(kdev);
 
@@ -2695,6 +2701,9 @@ void intel_runtime_pm_get_noresume(struct drm_i915_private *dev_priv)
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	struct device *kdev = &pdev->dev;
 
+	if (atomic_inc_not_zero(&dev_priv->pm.wakeref_count))
+		return;
+
 	assert_rpm_wakelock_held(dev_priv);
 	pm_runtime_get_noresume(kdev);
 
@@ -2714,8 +2723,10 @@ void intel_runtime_pm_put(struct drm_i915_private *dev_priv)
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	struct device *kdev = &pdev->dev;
 
+	if (!atomic_dec_and_test(&dev_priv->pm.wakeref_count))
+		return;
+
 	assert_rpm_wakelock_held(dev_priv);
-	atomic_dec(&dev_priv->pm.wakeref_count);
 
 	pm_runtime_mark_last_busy(kdev);
 	pm_runtime_put_autosuspend(kdev);
-- 
2.10.2