text: /*
   * SPDX-License-Identifier: MIT
   *
   * Copyright © 2018 Intel Corporation
   */
  
  #ifndef _I915_SCHEDULER_TYPES_H_
  #define _I915_SCHEDULER_TYPES_H_
  
  #include <linux/list.h>
  
  #include "gt/intel_engine_types.h"
  #include "i915_priolist_types.h"
  
  struct drm_i915_private;
  struct i915_request;
  struct intel_engine_cs;
  
  struct i915_sched_attr {
  	/**
  	 * @priority: execution and service priority
  	 *
  	 * All clients are equal, but some are more equal than others!
  	 *
  	 * Requests from a context with a greater (more positive) value of
  	 * @priority will be executed before those with a lower @priority
  	 * value, forming a simple QoS.
  	 *
  	 * The &drm_i915_private.kernel_context is assigned the lowest priority.
  	 */
  	int priority;
  };
  
  /*
   * "People assume that time is a strict progression of cause to effect, but
   * actually, from a nonlinear, non-subjective viewpoint, it's more like a big
   * ball of wibbly-wobbly, timey-wimey ... stuff." -The Doctor, 2015
   *
   * Requests exist in a complex web of interdependencies. Each request
   * has to wait for some other request to complete before it is ready to be run
   * (e.g. we have to wait until the pixels have been rendering into a texture
   * before we can copy from it). We track the readiness of a request in terms
   * of fences, but we also need to keep the dependency tree for the lifetime
   * of the request (beyond the life of an individual fence). We use the tree
   * at various points to reorder the requests whilst keeping the requests
   * in order with respect to their various dependencies.
   *
   * There is no active component to the "scheduler". As we know the dependency
   * DAG of each request, we are able to insert it into a sorted queue when it
   * is ready, and are able to reorder its portion of the graph to accommodate
   * dynamic priority changes.
   *
   * Ok, there is now one active element to the "scheduler" in the backends.
   * We let a new context run for a small amount of time before re-evaluating
   * the run order. As we re-evaluate, we maintain the strict ordering of
   * dependencies, but attempt to rotate the active contexts (the current context
   * is put to the back of its priority queue, then reshuffling its dependents).
   * This provides minimal timeslicing and prevents a userspace hog (e.g.
   * something waiting on a user semaphore [VkEvent]) from denying service to
   * others.
   */
  struct i915_sched_node {
  	struct list_head signalers_list; /* those before us, we depend upon */
  	struct list_head waiters_list; /* those after us, they depend upon us */
  	struct list_head link;
  	struct i915_sched_attr attr;
  	unsigned int flags;
  #define I915_SCHED_HAS_SEMAPHORE_CHAIN	BIT(0)
  	intel_engine_mask_t semaphores;
  };
  
  struct i915_dependency {
  	struct i915_sched_node *signaler;
  	struct i915_sched_node *waiter;
  	struct list_head signal_link;
  	struct list_head wait_link;
  	struct list_head dfs_link;
  	unsigned long flags;
  #define I915_DEPENDENCY_ALLOC		BIT(0)
  #define I915_DEPENDENCY_EXTERNAL	BIT(1)
  };
  
  #endif /* _I915_SCHEDULER_TYPES_H_ */
  