xref: /netbsd-src/sys/external/bsd/drm2/dist/drm/i915/i915_scheduler_types.h (revision 41ec02673d281bbb3d38e6c78504ce6e30c228c1)
1 /*	$NetBSD: i915_scheduler_types.h,v 1.2 2021/12/18 23:45:28 riastradh Exp $	*/
2 
3 /*
4  * SPDX-License-Identifier: MIT
5  *
6  * Copyright © 2018 Intel Corporation
7  */
8 
9 #ifndef _I915_SCHEDULER_TYPES_H_
10 #define _I915_SCHEDULER_TYPES_H_
11 
12 #include <linux/list.h>
13 
14 #include "gt/intel_engine_types.h"
15 #include "i915_priolist_types.h"
16 
17 struct drm_i915_private;
18 struct i915_request;
19 struct intel_engine_cs;
20 
21 struct i915_sched_attr {
22 	/**
23 	 * @priority: execution and service priority
24 	 *
25 	 * All clients are equal, but some are more equal than others!
26 	 *
27 	 * Requests from a context with a greater (more positive) value of
28 	 * @priority will be executed before those with a lower @priority
29 	 * value, forming a simple QoS.
30 	 *
31 	 * The &drm_i915_private.kernel_context is assigned the lowest priority.
32 	 */
33 	int priority;
34 };
35 
36 /*
37  * "People assume that time is a strict progression of cause to effect, but
38  * actually, from a nonlinear, non-subjective viewpoint, it's more like a big
39  * ball of wibbly-wobbly, timey-wimey ... stuff." -The Doctor, 2015
40  *
41  * Requests exist in a complex web of interdependencies. Each request
42  * has to wait for some other request to complete before it is ready to be run
43  * (e.g. we have to wait until the pixels have been rendering into a texture
44  * before we can copy from it). We track the readiness of a request in terms
45  * of fences, but we also need to keep the dependency tree for the lifetime
46  * of the request (beyond the life of an individual fence). We use the tree
47  * at various points to reorder the requests whilst keeping the requests
48  * in order with respect to their various dependencies.
49  *
50  * There is no active component to the "scheduler". As we know the dependency
51  * DAG of each request, we are able to insert it into a sorted queue when it
52  * is ready, and are able to reorder its portion of the graph to accommodate
53  * dynamic priority changes.
54  *
55  * Ok, there is now one active element to the "scheduler" in the backends.
56  * We let a new context run for a small amount of time before re-evaluating
57  * the run order. As we re-evaluate, we maintain the strict ordering of
58  * dependencies, but attempt to rotate the active contexts (the current context
59  * is put to the back of its priority queue, then reshuffling its dependents).
60  * This provides minimal timeslicing and prevents a userspace hog (e.g.
61  * something waiting on a user semaphore [VkEvent]) from denying service to
62  * others.
63  */
64 struct i915_sched_node {
65 	struct list_head signalers_list; /* those before us, we depend upon */
66 	struct list_head waiters_list; /* those after us, they depend upon us */
67 	struct list_head link;
68 	struct i915_sched_attr attr;
69 	unsigned int flags;
70 #define I915_SCHED_HAS_SEMAPHORE_CHAIN	BIT(0)
71 	intel_engine_mask_t semaphores;
72 };
73 
74 struct i915_dependency {
75 	struct i915_sched_node *signaler;
76 	struct i915_sched_node *waiter;
77 	struct list_head signal_link;
78 	struct list_head wait_link;
79 	struct list_head dfs_link;
80 	unsigned long flags;
81 #define I915_DEPENDENCY_ALLOC		BIT(0)
82 #define I915_DEPENDENCY_EXTERNAL	BIT(1)
83 };
84 
85 #endif /* _I915_SCHEDULER_TYPES_H_ */
86