1 /*
2  * SPDX-License-Identifier: MIT
3  *
4  * Copyright © 2018 Intel Corporation
5  */
6 
7 #ifndef _I915_SCHEDULER_TYPES_H_
8 #define _I915_SCHEDULER_TYPES_H_
9 
10 #include <linux/list.h>
11 
12 #include "gt/intel_engine_types.h"
13 #include "i915_priolist_types.h"
14 
15 struct drm_i915_private;
16 struct i915_request;
17 struct intel_engine_cs;
18 
19 struct i915_sched_attr {
20 	/**
21 	 * @priority: execution and service priority
22 	 *
23 	 * All clients are equal, but some are more equal than others!
24 	 *
25 	 * Requests from a context with a greater (more positive) value of
26 	 * @priority will be executed before those with a lower @priority
27 	 * value, forming a simple QoS.
28 	 *
29 	 * The &drm_i915_private.kernel_context is assigned the lowest priority.
30 	 */
31 	int priority;
32 };
33 
34 /*
35  * "People assume that time is a strict progression of cause to effect, but
36  * actually, from a nonlinear, non-subjective viewpoint, it's more like a big
37  * ball of wibbly-wobbly, timey-wimey ... stuff." -The Doctor, 2015
38  *
39  * Requests exist in a complex web of interdependencies. Each request
40  * has to wait for some other request to complete before it is ready to be run
41  * (e.g. we have to wait until the pixels have been rendering into a texture
42  * before we can copy from it). We track the readiness of a request in terms
43  * of fences, but we also need to keep the dependency tree for the lifetime
44  * of the request (beyond the life of an individual fence). We use the tree
45  * at various points to reorder the requests whilst keeping the requests
46  * in order with respect to their various dependencies.
47  *
48  * There is no active component to the "scheduler". As we know the dependency
49  * DAG of each request, we are able to insert it into a sorted queue when it
50  * is ready, and are able to reorder its portion of the graph to accommodate
51  * dynamic priority changes.
52  *
53  * Ok, there is now one active element to the "scheduler" in the backends.
54  * We let a new context run for a small amount of time before re-evaluating
55  * the run order. As we re-evaluate, we maintain the strict ordering of
56  * dependencies, but attempt to rotate the active contexts (the current context
57  * is put to the back of its priority queue, then reshuffling its dependents).
58  * This provides minimal timeslicing and prevents a userspace hog (e.g.
59  * something waiting on a user semaphore [VkEvent]) from denying service to
60  * others.
61  */
62 struct i915_sched_node {
63 	struct list_head signalers_list; /* those before us, we depend upon */
64 	struct list_head waiters_list; /* those after us, they depend upon us */
65 	struct list_head link;
66 	struct i915_sched_attr attr;
67 	unsigned int flags;
68 #define I915_SCHED_HAS_EXTERNAL_CHAIN	BIT(0)
69 	intel_engine_mask_t semaphores;
70 };
71 
72 struct i915_dependency {
73 	struct i915_sched_node *signaler;
74 	struct i915_sched_node *waiter;
75 	struct list_head signal_link;
76 	struct list_head wait_link;
77 	struct list_head dfs_link;
78 	unsigned long flags;
79 #define I915_DEPENDENCY_ALLOC		BIT(0)
80 #define I915_DEPENDENCY_EXTERNAL	BIT(1)
81 #define I915_DEPENDENCY_WEAK		BIT(2)
82 };
83 
84 #endif /* _I915_SCHEDULER_TYPES_H_ */
85