/*
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* SPDX-License-Identifier: MIT
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*
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* Copyright © 2018 Intel Corporation
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*/
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#ifndef _I915_SCHEDULER_TYPES_H_
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#define _I915_SCHEDULER_TYPES_H_
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#include <linux/list.h>
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#include "gt/intel_engine_types.h"
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#include "i915_priolist_types.h"
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struct drm_i915_private;
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struct i915_request;
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struct intel_engine_cs;
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struct i915_sched_attr {
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/**
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* @priority: execution and service priority
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*
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* All clients are equal, but some are more equal than others!
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*
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* Requests from a context with a greater (more positive) value of
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* @priority will be executed before those with a lower @priority
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* value, forming a simple QoS.
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*
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* The &drm_i915_private.kernel_context is assigned the lowest priority.
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*/
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int priority;
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};
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/*
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* "People assume that time is a strict progression of cause to effect, but
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* actually, from a nonlinear, non-subjective viewpoint, it's more like a big
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* ball of wibbly-wobbly, timey-wimey ... stuff." -The Doctor, 2015
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*
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* Requests exist in a complex web of interdependencies. Each request
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* has to wait for some other request to complete before it is ready to be run
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* (e.g. we have to wait until the pixels have been rendering into a texture
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* before we can copy from it). We track the readiness of a request in terms
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* of fences, but we also need to keep the dependency tree for the lifetime
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* of the request (beyond the life of an individual fence). We use the tree
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* at various points to reorder the requests whilst keeping the requests
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* in order with respect to their various dependencies.
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*
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* There is no active component to the "scheduler". As we know the dependency
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* DAG of each request, we are able to insert it into a sorted queue when it
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* is ready, and are able to reorder its portion of the graph to accommodate
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* dynamic priority changes.
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*
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* Ok, there is now one active element to the "scheduler" in the backends.
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* We let a new context run for a small amount of time before re-evaluating
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* the run order. As we re-evaluate, we maintain the strict ordering of
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* dependencies, but attempt to rotate the active contexts (the current context
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* is put to the back of its priority queue, then reshuffling its dependents).
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* This provides minimal timeslicing and prevents a userspace hog (e.g.
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* something waiting on a user semaphore [VkEvent]) from denying service to
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* others.
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*/
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struct i915_sched_node {
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struct list_head signalers_list; /* those before us, we depend upon */
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struct list_head waiters_list; /* those after us, they depend upon us */
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struct list_head link;
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struct i915_sched_attr attr;
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unsigned int flags;
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#define I915_SCHED_HAS_EXTERNAL_CHAIN BIT(0)
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intel_engine_mask_t semaphores;
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};
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struct i915_dependency {
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struct i915_sched_node *signaler;
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struct i915_sched_node *waiter;
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struct list_head signal_link;
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struct list_head wait_link;
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struct list_head dfs_link;
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unsigned long flags;
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#define I915_DEPENDENCY_ALLOC BIT(0)
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#define I915_DEPENDENCY_EXTERNAL BIT(1)
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#define I915_DEPENDENCY_WEAK BIT(2)
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};
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#endif /* _I915_SCHEDULER_TYPES_H_ */
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