1 files changed, 102 insertions, 0 deletions
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_throttle.c b/drivers/gpu/drm/i915/gem/i915_gem_throttle.c
new file mode 100644
index 000000000..af85d0c28
--- /dev/null
+++ b/drivers/gpu/drm/i915/gem/i915_gem_throttle.c
@@ -0,0 +1,102 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2014-2016 Intel Corporation
+ */
+
+#include <linux/jiffies.h>
+
+#include <drm/drm_file.h>
+
+#include "i915_drv.h"
+#include "i915_file_private.h"
+#include "i915_gem_context.h"
+#include "i915_gem_ioctls.h"
+#include "i915_gem_object.h"
+
+/*
+ * 20ms is a fairly arbitrary limit (greater than the average frame time)
+ * chosen to prevent the CPU getting more than a frame ahead of the GPU
+ * (when using lax throttling for the frontbuffer). We also use it to
+ * offer free GPU waitboosts for severely congested workloads.
+ */
+#define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
+
+/*
+ * Throttle our rendering by waiting until the ring has completed our requests
+ * emitted over 20 msec ago.
+ *
+ * Note that if we were to use the current jiffies each time around the loop,
+ * we wouldn't escape the function with any frames outstanding if the time to
+ * render a frame was over 20ms.
+ *
+ * This should get us reasonable parallelism between CPU and GPU but also
+ * relatively low latency when blocking on a particular request to finish.
+ */
+int
+i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
+			struct drm_file *file)
+{
+	const unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
+	struct drm_i915_file_private *file_priv = file->driver_priv;
+	struct drm_i915_private *i915 = to_i915(dev);
+	struct i915_gem_context *ctx;
+	unsigned long idx;
+	long ret;
+
+	/* ABI: return -EIO if already wedged */
+	ret = intel_gt_terminally_wedged(to_gt(i915));
+	if (ret)
+		return ret;
+
+	rcu_read_lock();
+	xa_for_each(&file_priv->context_xa, idx, ctx) {
+		struct i915_gem_engines_iter it;
+		struct intel_context *ce;
+
+		if (!kref_get_unless_zero(&ctx->ref))
+			continue;
+		rcu_read_unlock();
+
+		for_each_gem_engine(ce,
+				    i915_gem_context_lock_engines(ctx),
+				    it) {
+			struct i915_request *rq, *target = NULL;
+
+			if (!ce->timeline)
+				continue;
+
+			mutex_lock(&ce->timeline->mutex);
+			list_for_each_entry_reverse(rq,
+						    &ce->timeline->requests,
+						    link) {
+				if (i915_request_completed(rq))
+					break;
+
+				if (time_after(rq->emitted_jiffies,
+					       recent_enough))
+					continue;
+
+				target = i915_request_get(rq);
+				break;
+			}
+			mutex_unlock(&ce->timeline->mutex);
+			if (!target)
+				continue;
+
+			ret = i915_request_wait(target,
+						I915_WAIT_INTERRUPTIBLE,
+						MAX_SCHEDULE_TIMEOUT);
+			i915_request_put(target);
+			if (ret < 0)
+				break;
+		}
+		i915_gem_context_unlock_engines(ctx);
+		i915_gem_context_put(ctx);
+
+		rcu_read_lock();
+	}
+	rcu_read_unlock();
+
+	return ret < 0 ? ret : 0;
+}