[PATCH 40/40] rps-double-boost-nospin

[Chris Wilson]

---
 drivers/gpu/drm/i915/i915_debugfs.c     |  3 +--
 drivers/gpu/drm/i915/i915_drv.h         |  2 +-
 drivers/gpu/drm/i915/i915_gem_request.c |  2 +-
 drivers/gpu/drm/i915/i915_irq.c         |  2 +-
 drivers/gpu/drm/i915/intel_gt_pm.c      | 18 +++++++++++-------
 drivers/gpu/drm/i915/intel_pm.c         |  2 --
 6 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index fdb2c71888c1..5989c6ab86a5 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2162,8 +2162,7 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 	seq_printf(m, "GPU busy? %s [%d requests]\n",
 		   yesno(dev_priv->gt.awake), dev_priv->gt.active_requests);
 	seq_printf(m, "CPU waiting? %d\n", count_irq_waiters(dev_priv));
-	seq_printf(m, "Boosts outstanding? %d\n",
-		   atomic_read(&rps->num_waiters));
+	seq_printf(m, "Boosts outstanding? %d\n", READ_ONCE(rps->num_waiters));
 	seq_printf(m, "Frequency requested %d\n",
 		   intel_gpu_freq(dev_priv, rps->cur_freq));
 	seq_printf(m, "  min hard:%d, soft:%d; max soft:%d, hard:%d\n",
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d235b0bfb89a..f61e55d4ffec 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -932,7 +932,7 @@ struct intel_rps {
 	enum { LOW_POWER, BETWEEN, HIGH_POWER } power;
 
 	bool enabled;
-	atomic_t num_waiters;
+	unsigned int num_waiters;
 	atomic_t boosts;
 
 	/* manual wa residency calculations */
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index fe4ce873501b..e7291019a573 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -441,7 +441,7 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 
 	spin_lock_irq(&request->lock);
 	if (request->waitboost)
-		atomic_dec(&request->i915->gt_pm.rps.num_waiters);
+		request->i915->gt_pm.rps.num_waiters--;
 	if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags))
 		dma_fence_signal_locked(&request->fence);
 	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index ea290f102784..a59ecd550d73 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1192,7 +1192,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	spin_lock_irq(&dev_priv->irq_lock);
 	if (rps->interrupts_enabled) {
 		pm_iir = fetch_and_zero(&rps->pm_iir);
-		client_boost = atomic_read(&rps->num_waiters);
+		client_boost = READ_ONCE(rps->num_waiters);
 	}
 	spin_unlock_irq(&dev_priv->irq_lock);
 
diff --git a/drivers/gpu/drm/i915/intel_gt_pm.c b/drivers/gpu/drm/i915/intel_gt_pm.c
index 088ed443dfc7..7a328896de82 100644
--- a/drivers/gpu/drm/i915/intel_gt_pm.c
+++ b/drivers/gpu/drm/i915/intel_gt_pm.c
@@ -478,7 +478,6 @@ void gen6_rps_boost(struct drm_i915_gem_request *rq,
 		    struct intel_rps_client *rps_client)
 {
 	struct intel_rps *rps = &rq->i915->gt_pm.rps;
-	unsigned long flags;
 	bool boost;
 
 	/* This is intentionally racy! We peek at the state here, then
@@ -487,14 +486,19 @@ void gen6_rps_boost(struct drm_i915_gem_request *rq,
 	if (!rps->enabled)
 		return;
 
+	if (rq->waitboost)
+		return;
+
 	boost = false;
-	spin_lock_irqsave(&rq->lock, flags);
-	if (!rq->waitboost && !i915_gem_request_completed(rq)) {
-		atomic_inc(&rps->num_waiters);
-		rq->waitboost = true;
-		boost = true;
+	if (!cmpxchg(&rq->waitboost, false, true)) {
+		unsigned long flags;
+
+		/* Serialize with i915_gem_request_retire() */
+		spin_lock_irqsave(&rq->lock, flags);
+		if (!i915_gem_request_completed(rq))
+			boost = !rps->num_waiters++;
+		spin_unlock_irqrestore(&rq->lock, flags);
 	}
-	spin_unlock_irqrestore(&rq->lock, flags);
 	if (!boost)
 		return;
 
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 5d88b164acfc..d9c2f7fbd402 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7034,8 +7034,6 @@ void intel_pm_setup(struct drm_i915_private *dev_priv)
 {
 	mutex_init(&dev_priv->pcu_lock);
 
-	atomic_set(&dev_priv->gt_pm.rps.num_waiters, 0);
-
 	dev_priv->runtime_pm.suspended = false;
 	atomic_set(&dev_priv->runtime_pm.wakeref_count, 0);
 }
-- 
2.15.1