1/*
 2 * SPDX-License-Identifier: MIT
 3 *
 4 * Copyright © 2014-2016 Intel Corporation
 5 */
 6
 7#include <linux/jiffies.h>
 8
 9#include <drm/drm_file.h>
10
11#include "i915_drv.h"
12#include "i915_gem_ioctls.h"
13#include "i915_gem_object.h"
14
15/*
16 * 20ms is a fairly arbitrary limit (greater than the average frame time)
17 * chosen to prevent the CPU getting more than a frame ahead of the GPU
18 * (when using lax throttling for the frontbuffer). We also use it to
19 * offer free GPU waitboosts for severely congested workloads.
20 */
21#define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
22
23/*
24 * Throttle our rendering by waiting until the ring has completed our requests
25 * emitted over 20 msec ago.
26 *
27 * Note that if we were to use the current jiffies each time around the loop,
28 * we wouldn't escape the function with any frames outstanding if the time to
29 * render a frame was over 20ms.
30 *
31 * This should get us reasonable parallelism between CPU and GPU but also
32 * relatively low latency when blocking on a particular request to finish.
33 */
34int
35i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
36			struct drm_file *file)
37{
38	struct drm_i915_file_private *file_priv = file->driver_priv;
39	unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
40	struct i915_request *request, *target = NULL;
41	long ret;
42
43	/* ABI: return -EIO if already wedged */
44	ret = intel_gt_terminally_wedged(&to_i915(dev)->gt);
45	if (ret)
46		return ret;
47
48	spin_lock(&file_priv->mm.lock);
49	list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
50		if (time_after_eq(request->emitted_jiffies, recent_enough))
51			break;
52
53		if (target) {
54			list_del(&target->client_link);
55			target->file_priv = NULL;
56		}
57
58		target = request;
59	}
60	if (target)
61		i915_request_get(target);
62	spin_unlock(&file_priv->mm.lock);
63
64	if (!target)
65		return 0;
66
67	ret = i915_request_wait(target,
68				I915_WAIT_INTERRUPTIBLE,
69				MAX_SCHEDULE_TIMEOUT);
70	i915_request_put(target);
71
72	return ret < 0 ? ret : 0;
73}