path: root/drivers/gpu/drm/scheduler/sched_main.c

/*
 * Copyright 2015 Advanced Micro Devices, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 */

/**
 * DOC: Overview
 *
 * The GPU scheduler provides entities which allow userspace to push jobs
 * into software queues which are then scheduled on a hardware run queue.
 * The software queues have a priority among them. The scheduler selects the entities
 * from the run queue using a FIFO. The scheduler provides dependency handling
 * features among jobs. The driver is supposed to provide callback functions for
 * backend operations to the scheduler like submitting a job to hardware run queue,
 * returning the dependencies of a job etc.
 *
 * The organisation of the scheduler is the following:
 *
 * 1. Each hw run queue has one scheduler
 * 2. Each scheduler has multiple run queues with different priorities
 *    (e.g., HIGH_HW,HIGH_SW, KERNEL, NORMAL)
 * 3. Each scheduler run queue has a queue of entities to schedule
 * 4. Entities themselves maintain a queue of jobs that will be scheduled on
 *    the hardware.
 *
 * The jobs in a entity are always scheduled in the order that they were pushed.
 *
 * Note that once a job was taken from the entities queue and pushed to the
 * hardware, i.e. the pending queue, the entity must not be referenced anymore
 * through the jobs entity pointer.
 */

/**
 * DOC: Flow Control
 *
 * The DRM GPU scheduler provides a flow control mechanism to regulate the rate
 * in which the jobs fetched from scheduler entities are executed.
 *
 * In this context the &drm_gpu_scheduler keeps track of a driver specified
 * credit limit representing the capacity of this scheduler and a credit count;
 * every &drm_sched_job carries a driver specified number of credits.
 *
 * Once a job is executed (but not yet finished), the job's credits contribute
 * to the scheduler's credit count until the job is finished. If by executing
 * one more job the scheduler's credit count would exceed the scheduler's
 * credit limit, the job won't be executed. Instead, the scheduler will wait
 * until the credit count has decreased enough to not overflow its credit limit.
 * This implies waiting for previously executed jobs.
 *
 * Optionally, drivers may register a callback (update_job_credits) provided by
 * struct drm_sched_backend_ops to update the job's credits dynamically. The
 * scheduler executes this callback every time the scheduler considers a job for
 * execution and subsequently checks whether the job fits the scheduler's credit
 * limit.
 */

#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/completion.h>
#include <linux/dma-resv.h>
#include <uapi/linux/sched/types.h>

#include <drm/drm_print.h>
#include <drm/drm_gem.h>
#include <drm/drm_syncobj.h>
#include <drm/gpu_scheduler.h>
#include <drm/spsc_queue.h>

#define CREAT