drivers/gpu/drm/i915/i915_scheduler_types.h

/*
 * 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_EXTERNAL_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)
#define I915_DEPENDENCY_WEAK		BIT(2)
};

#define for_each_waiter(p__, rq__) \
	list_for_each_entry_lockless(p__, \
				     &(rq__)->sched.waiters_list, \
				     wait_link)

#define for_each_signaler(p__, rq__) \
	list_for_each_entry_rcu(p__, \
				&(rq__)->sched.signalers_list, \
				signal_link)

/**
 * struct i915_sched_engine - scheduler engine
 *
 * A schedule engine represents a submission queue with different priority
 * bands. It contains all the common state (relative to the backend) to queue,
 * track, and submit a request.
 *
 * This object at the moment is quite i915 specific but will transition into a
 * container for the drm_gpu_scheduler plus a few other variables once the i915
 * is integrated with the DRM scheduler.
 */
struct i915_sched_engine {
	/**
	 * @ref: reference count of schedule engine object
	 */
	struct kref ref;

	/**
	 * @lock: protects requests in priority lists, requests, hold and
	 * tasklet while running
	 */
	spinlock_t lock;

	/**
	 * @requests: list of requests inflight on this schedule engine
	 */
	struct list_head requests;

	/**
	 * @hold: list of ready requests, but on hold
	 */
	struct list_head hold;

	/**
	 * @tasklet: softirq tasklet for submission
	 */
	struct tasklet_struct tasklet;

	/**
	 * @default_priolist: priority list for I915_PRIORITY_NORMAL
	 */
	struct i915_priolist default_priolist;

	/**
	 * @queue_priority_hint: Highest pending priority.
	 *
	 * When we add requests into the queue, or adjust the priority of
	 * executing requests, we compute the maximum priority of those
	 * pending requests. We can then use this value to determine if
	 * we need to preempt the executing requests to service the queue.
	 * However, since the we may have recorded the priority of an inflight
	 * request we wanted to preempt but since completed, at the time of
	 * dequeuing the priority hint may no longer may match the highest
	 * available request priority.
	 */
	int queue_priority_hint;

	/**
	 * @queue: queue of requests, in priority lists
	 */
	struct rb_root_cached queue;

	/**
	 * @no_priolist: priority lists disabled
	 */
	bool no_priolist;

	/**
	 * @private_data: private data of the submission backend
	 */
	void *private_data;

	/**
	 * @destroy: destroy schedule engine / cleanup in backend
	 */
	void	(*destroy)(struct kref *kref);

	/**
	 * @disabled: check if backend has disabled submission
	 */
	bool	(*disabled)(struct i915_sched_engine *sched_engine);

	/**
	 * @kick_backend: kick backend after a request's priority has changed
	 */
	void	(*kick_backend)(const struct i915_request *rq,
				int prio);

	/**
	 * @bump_inflight_request_prio: update priority of an inflight request
	 */
	void	(*bump_inflight_request_prio)(struct i915_request *rq,
					      int prio);

	/**
	 * @retire_inflight_request_prio: indicate request is retired to
	 * priority tracking
	 */
	void	(*retire_inflight_request_prio)(struct i915_request *rq);

	/**
	 * @schedule: adjust priority of request
	 *
	 * Call when the priority on a request has changed and it and its
	 * dependencies may need rescheduling. Note the request itself may
	 * not be ready to run!
	 */
	void	(*schedule)(struct i915_request *request,
			    const struct i915_sched_attr *attr);
};

#endif /* _I915_SCHEDULER_TYPES_H_ */