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_context.h"
13 #include "i915_gem_ioctls.h"
14 #include "i915_gem_object.h"
15 
16 /*
17  * 20ms is a fairly arbitrary limit (greater than the average frame time)
18  * chosen to prevent the CPU getting more than a frame ahead of the GPU
19  * (when using lax throttling for the frontbuffer). We also use it to
20  * offer free GPU waitboosts for severely congested workloads.
21  */
22 #define DRM_I915_THROTTLE_JIFFIES msecs_to_jiffies(20)
23 
24 /*
25  * Throttle our rendering by waiting until the ring has completed our requests
26  * emitted over 20 msec ago.
27  *
28  * Note that if we were to use the current jiffies each time around the loop,
29  * we wouldn't escape the function with any frames outstanding if the time to
30  * render a frame was over 20ms.
31  *
32  * This should get us reasonable parallelism between CPU and GPU but also
33  * relatively low latency when blocking on a particular request to finish.
34  */
35 int
36 i915_gem_throttle_ioctl(struct drm_device *dev, void *data,
37 			struct drm_file *file)
38 {
39 	const unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
40 	struct drm_i915_file_private *file_priv = file->driver_priv;
41 	struct i915_gem_context *ctx;
42 	unsigned long idx;
43 	long ret;
44 
45 	/* ABI: return -EIO if already wedged */
46 	ret = intel_gt_terminally_wedged(&to_i915(dev)->gt);
47 	if (ret)
48 		return ret;
49 
50 	rcu_read_lock();
51 	xa_for_each(&file_priv->context_xa, idx, ctx) {
52 		struct i915_gem_engines_iter it;
53 		struct intel_context *ce;
54 
55 		if (!kref_get_unless_zero(&ctx->ref))
56 			continue;
57 		rcu_read_unlock();
58 
59 		for_each_gem_engine(ce,
60 				    i915_gem_context_lock_engines(ctx),
61 				    it) {
62 			struct i915_request *rq, *target = NULL;
63 
64 			if (!ce->timeline)
65 				continue;
66 
67 			mutex_lock(&ce->timeline->mutex);
68 			list_for_each_entry_reverse(rq,
69 						    &ce->timeline->requests,
70 						    link) {
71 				if (i915_request_completed(rq))
72 					break;
73 
74 				if (time_after(rq->emitted_jiffies,
75 					       recent_enough))
76 					continue;
77 
78 				target = i915_request_get(rq);
79 				break;
80 			}
81 			mutex_unlock(&ce->timeline->mutex);
82 			if (!target)
83 				continue;
84 
85 			ret = i915_request_wait(target,
86 						I915_WAIT_INTERRUPTIBLE,
87 						MAX_SCHEDULE_TIMEOUT);
88 			i915_request_put(target);
89 			if (ret < 0)
90 				break;
91 		}
92 		i915_gem_context_unlock_engines(ctx);
93 		i915_gem_context_put(ctx);
94 
95 		rcu_read_lock();
96 	}
97 	rcu_read_unlock();
98 
99 	return ret < 0 ? ret : 0;
100 }
101