drivers/gpu/drm/i915/i915_scheduler_types.h

   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_SEMAPHORE_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 };
  82
  83 #endif /* _I915_SCHEDULER_TYPES_H_ */