1 files changed, 73 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 000000000000..adb3074d9ce2
--- /dev/null
+++ b/drivers/gpu/drm/i915/gem/i915_gem_throttle.c
@@ -0,0 +1,73 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2014-2016 Intel Corporation
+ */
+
+#include <linux/jiffies.h>
+
+#include <drm/drm_file.h>
+
+#include "i915_drv.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)
+{
+	struct drm_i915_file_private *file_priv = file->driver_priv;
+	unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
+	struct i915_request *request, *target = NULL;
+	long ret;
+
+	/* ABI: return -EIO if already wedged */
+	ret = i915_terminally_wedged(to_i915(dev));
+	if (ret)
+		return ret;
+
+	spin_lock(&file_priv->mm.lock);
+	list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
+		if (time_after_eq(request->emitted_jiffies, recent_enough))
+			break;
+
+		if (target) {
+			list_del(&target->client_link);
+			target->file_priv = NULL;
+		}
+
+		target = request;
+	}
+	if (target)
+		i915_request_get(target);
+	spin_unlock(&file_priv->mm.lock);
+
+	if (!target)
+		return 0;
+
+	ret = i915_request_wait(target,
+				I915_WAIT_INTERRUPTIBLE,
+				MAX_SCHEDULE_TIMEOUT);
+	i915_request_put(target);
+
+	return ret < 0 ? ret : 0;
+}