/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2018 Intel Corporation
 */

#include <linux/mutex.h>

#include "i915_drv.h"
#include "i915_globals.h"
#include "i915_request.h"
#include "i915_scheduler.h"

static struct i915_global_scheduler {
        struct i915_global base;
        struct kmem_cache *slab_dependencies;
        struct kmem_cache *slab_priorities;
} global;

static DEFINE_SPINLOCK(schedule_lock);

static const struct i915_request *
node_to_request(const struct i915_sched_node *node)
{
        return container_of(node, const struct i915_request, sched);
}

static inline bool node_started(const struct i915_sched_node *node)
{
        return i915_request_started(node_to_request(node));
}

static inline bool node_signaled(const struct i915_sched_node *node)
{
        return i915_request_completed(node_to_request(node));
}

static inline struct i915_priolist *to_priolist(struct rb_node *rb)
{
        return rb_entry(rb, struct i915_priolist, node);
}

static void assert_priolists(struct intel_engine_execlists * const execlists)
{
        struct rb_node *rb;
        long last_prio, i;

        if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
                return;

        GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
                   rb_first(&execlists->queue.rb_root));

        last_prio = (INT_MAX >> I915_USER_PRIORITY_SHIFT) + 1;
        for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
                const struct i915_priolist *p = to_priolist(rb);

                GEM_BUG_ON(p->priority >= last_prio);
                last_prio = p->priority;

                GEM_BUG_ON(!p->used);
                for (i = 0; i < ARRAY_SIZE(p->requests); i++) {
                        if (list_empty(&p->requests[i]))
                                continue;

                        GEM_BUG_ON(!(p->used & BIT(i)));
                }
        }
}

struct list_head *
i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
{
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct i915_priolist *p;
        struct rb_node **parent, *rb;
        bool first = true;
        int idx, i;

        lockdep_assert_held(&engine->active.lock);
        assert_priolists(execlists);

        /* buckets sorted from highest [in slot 0] to lowest priority */
        idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
        prio >>= I915_USER_PRIORITY_SHIFT;
        if (unlikely(execlists->no_priolist))
                prio = I915_PRIORITY_NORMAL;

find_priolist:
        /* most positive priority is scheduled first, equal priorities fifo */
        rb = NULL;
        parent = &execlists->queue.rb_root.rb_node;
        while (*parent) {
                rb = *parent;
                p = to_priolist(rb);
                if (prio > p->priority) {
                        parent = &rb->rb_left;
                } else if (prio < p->priority) {
                        parent = &rb->rb_right;
                        first = false;
                } else {
                        goto out;
                }
        }

        if (prio == I915_PRIORITY_NORMAL) {
                p = &execlists->default_priolist;
        } else {
                p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
                /* Convert an allocation failure to a priority bump */
                if (unlikely(!p)) {
                        prio = I915_PRIORITY_NORMAL; /* recurses just once */

                        /* To maintain ordering with all rendering, after an
                         * allocation failure we have to disable all scheduling.
                         * Requests will then be executed in fifo, and schedule
                         * will ensure that dependencies are emitted in fifo.
                         * There will be still some reordering with existing
                         * requests, so if userspace lied about their
                         * dependencies that reordering may be visible.
                         */
                        execlists->no_priolist = true;
                        goto find_priolist;
                }
        }

        p->priority = prio;
        for (i = 0; i < ARRAY_SIZE(p->requests); i++)
                INIT_LIST_HEAD(&p->requests[i]);
        rb_link_node(&p->node, rb, parent);
        rb_insert_color_cached(&p->node, &execlists->queue, first);
        p->used = 0;

out:
        p->used |= BIT(idx);
        return &p->requests[idx];
}

void __i915_priolist_free(struct i915_priolist *p)
{
        kmem_cache_free(global.slab_priorities, p);
}

struct sched_cache {
        struct list_head *priolist;
};

static struct intel_engine_cs *
sched_lock_engine(const struct i915_sched_node *node,
                  struct intel_engine_cs *locked,
                  struct sched_cache *cache)
{
        const struct i915_request *rq = node_to_request(node);
        struct intel_engine_cs *engine;

        GEM_BUG_ON(!locked);

        /*
         * Virtual engines complicate acquiring the engine timeline lock,
         * as their rq->engine pointer is not stable until under that
         * engine lock. The simple ploy we use is to take the lock then
         * check that the rq still belongs to the newly locked engine.
         */
        while (locked != (engine = READ_ONCE(rq->engine))) {
                spin_unlock(&locked->active.lock);
                memset(cache, 0, sizeof(*cache));
                spin_lock(&engine->active.lock);
                locked = engine;
        }

        GEM_BUG_ON(locked != engine);
        return locked;
}

static inline int rq_prio(const struct i915_request *rq)
{
        return rq->sched.attr.priority | __NO_PREEMPTION;
}

static inline bool need_preempt(int prio, int active)
{
        /*
         * Allow preemption of low -> normal -> high, but we do
         * not allow low priority tasks to preempt other low priority
         * tasks under the impression that latency for low priority
         * tasks does not matter (as much as background throughput),
         * so kiss.
         */
        return prio >= max(I915_PRIORITY_NORMAL, active);
}

static void kick_submission(struct intel_engine_cs *engine,
                            const struct i915_request *rq,
                            int prio)
{
        const struct i915_request *inflight;

        /*
         * We only need to kick the tasklet once for the high priority
         * new context we add into the queue.
         */
        if (prio <= engine->execlists.queue_priority_hint)
                return;

        rcu_read_lock();

        /* Nothing currently active? We're overdue for a submission! */
        inflight = execlists_active(&engine->execlists);
        if (!inflight)
                goto unlock;

        /*
         * If we are already the currently executing context, don't
         * bother evaluating if we should preempt ourselves, or if
         * we expect nothing to change as a result of running the
         * tasklet, i.e. we have not change the priority queue
         * sufficiently to oust the running context.
         */
        if (inflight->hw_context == rq->hw_context)
                goto unlock;

        engine->execlists.queue_priority_hint = prio;
        if (need_preempt(prio, rq_prio(inflight)))
                tasklet_hi_schedule(&engine->execlists.tasklet);

unlock:
        rcu_read_unlock();
}

static void __i915_schedule(struct i915_sched_node *node,
                            const struct i915_sched_attr *attr)
{
        struct intel_engine_cs *engine;
        struct i915_dependency *dep, *p;
        struct i915_dependency stack;
        const int prio = attr->priority;
        struct sched_cache cache;
        LIST_HEAD(dfs);

        /* Needed in order to use the temporary link inside i915_dependency */
        lockdep_assert_held(&schedule_lock);
        GEM_BUG_ON(prio == I915_PRIORITY_INVALID);

        if (prio <= READ_ONCE(node->attr.priority))
                return;

        if (node_signaled(node))
                return;

        stack.signaler = node;
        list_add(&stack.dfs_link, &dfs);

        /*
         * Recursively bump all dependent priorities to match the new request.
         *
         * A naive approach would be to use recursion:
         * static void update_priorities(struct i915_sched_node *node, prio) {
         *      list_for_each_entry(dep, &node->signalers_list, signal_link)
         *              update_priorities(dep->signal, prio)
         *      queue_request(node);
         * }
         * but that may have unlimited recursion depth and so runs a very
         * real risk of overunning the kernel stack. Instead, we build
         * a flat list of all dependencies starting with the current request.
         * As we walk the list of dependencies, we add all of its dependencies
         * to the end of the list (this may include an already visited
         * request) and continue to walk onwards onto the new dependencies. The
         * end result is a topological list of requests in reverse order, the
         * last element in the list is the request we must execute first.
         */
        list_for_each_entry(dep, &dfs, dfs_link) {
                struct i915_sched_node *node = dep->signaler;

                /* If we are already flying, we know we have no signalers */
                if (node_started(node))
                        continue;

                /*
                 * Within an engine, there can be no cycle, but we may
                 * refer to the same dependency chain multiple times
                 * (redundant dependencies are not eliminated) and across
                 * engines.
                 */
                list_for_each_entry(p, &node->signalers_list, signal_link) {
                        GEM_BUG_ON(p == dep); /* no cycles! */

                        if (node_signaled(p->signaler))
                                continue;

                        if (prio > READ_ONCE(p->signaler->attr.priority))
                                list_move_tail(&p->dfs_link, &dfs);
                }
        }

        /*
         * If we didn't need to bump any existing priorities, and we haven't
         * yet submitted this request (i.e. there is no potential race with
         * execlists_submit_request()), we can set our own priority and skip
         * acquiring the engine locks.
         */
        if (node->attr.priority == I915_PRIORITY_INVALID) {
                GEM_BUG_ON(!list_empty(&node->link));
                node->attr = *attr;

                if (stack.dfs_link.next == stack.dfs_link.prev)
                        return;

                __list_del_entry(&stack.dfs_link);
        }

        memset(&cache, 0, sizeof(cache));
        engine = node_to_request(node)->engine;
        spin_lock(&engine->active.lock);

        /* Fifo and depth-first replacement ensure our deps execute before us */
        engine = sched_lock_engine(node, engine, &cache);
        list_for_each_entry_safe_reverse(dep, p, &dfs, dfs_link) {
                INIT_LIST_HEAD(&dep->dfs_link);

                node = dep->signaler;
                engine = sched_lock_engine(node, engine, &cache);
                lockdep_assert_held(&engine->active.lock);

                /* Recheck after acquiring the engine->timeline.lock */
                if (prio <= node->attr.priority || node_signaled(node))
                        continue;

                GEM_BUG_ON(node_to_request(node)->engine != engine);

                node->attr.priority = prio;

                if (list_empty(&node->link)) {
                        /*
                         * If the request is not in the priolist queue because
                         * it is not yet runnable, then it doesn't contribute
                         * to our preemption decisions. On the other hand,
                         * if the request is on the HW, it too is not in the
                         * queue; but in that case we may still need to reorder
                         * the inflight requests.
                         */
                        continue;
                }

                if (!intel_engine_is_virtual(engine) &&
                    !i915_request_is_active(node_to_request(node))) {
                        if (!cache.priolist)
                                cache.priolist =
                                        i915_sched_lookup_priolist(engine,
                                                                   prio);
                        list_move_tail(&node->link, cache.priolist);
                }

                /* Defer (tasklet) submission until after all of our updates. */
                kick_submission(engine, node_to_request(node), prio);
        }

        spin_unlock(&engine->active.lock);
}

void i915_schedule(struct i915_request *rq, const struct i915_sched_attr *attr)
{
        spin_lock_irq(&schedule_lock);
        __i915_schedule(&rq->sched, attr);
        spin_unlock_irq(&schedule_lock);
}

static void __bump_priority(struct i915_sched_node *node, unsigned int bump)
{
        struct i915_sched_attr attr = node->attr;

        attr.priority |= bump;
        __i915_schedule(node, &attr);
}

void i915_schedule_bump_priority(struct i915_request *rq, unsigned int bump)
{
        unsigned long flags;

        GEM_BUG_ON(bump & ~I915_PRIORITY_MASK);
        if (READ_ONCE(rq->sched.attr.priority) & bump)
                return;

        spin_lock_irqsave(&schedule_lock, flags);
        __bump_priority(&rq->sched, bump);
        spin_unlock_irqrestore(&schedule_lock, flags);
}

void i915_sched_node_init(struct i915_sched_node *node)
{
        INIT_LIST_HEAD(&node->signalers_list);
        INIT_LIST_HEAD(&node->waiters_list);
        INIT_LIST_HEAD(&node->link);
        node->attr.priority = I915_PRIORITY_INVALID;
        node->semaphores = 0;
        node->flags = 0;
}

static struct i915_dependency *
i915_dependency_alloc(void)
{
        return kmem_cache_alloc(global.slab_dependencies, GFP_KERNEL);
}

static void
i915_dependency_free(struct i915_dependency *dep)
{
        kmem_cache_free(global.slab_dependencies, dep);
}

bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
                                      struct i915_sched_node *signal,
                                      struct i915_dependency *dep,
                                      unsigned long flags)
{
        bool ret = false;

        spin_lock_irq(&schedule_lock);

        if (!node_signaled(signal)) {
                INIT_LIST_HEAD(&dep->dfs_link);
                list_add(&dep->wait_link, &signal->waiters_list);
                list_add(&dep->signal_link, &node->signalers_list);
                dep->signaler = signal;
                dep->waiter = node;
                dep->flags = flags;

                /* Keep track of whether anyone on this chain has a semaphore */
                if (signal->flags & I915_SCHED_HAS_SEMAPHORE_CHAIN &&
                    !node_started(signal))
                        node->flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;

                /*
                 * As we do not allow WAIT to preempt inflight requests,
                 * once we have executed a request, along with triggering
                 * any execution callbacks, we must preserve its ordering
                 * within the non-preemptible FIFO.
                 */
                BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK);
                if (flags & I915_DEPENDENCY_EXTERNAL)
                        __bump_priority(signal, __NO_PREEMPTION);

                ret = true;
        }

        spin_unlock_irq(&schedule_lock);

        return ret;
}

int i915_sched_node_add_dependency(struct i915_sched_node *node,
                                   struct i915_sched_node *signal)
{
        struct i915_dependency *dep;

        dep = i915_dependency_alloc();
        if (!dep)
                return -ENOMEM;

        if (!__i915_sched_node_add_dependency(node, signal, dep,
                                              I915_DEPENDENCY_EXTERNAL |
                                              I915_DEPENDENCY_ALLOC))
                i915_dependency_free(dep);

        return 0;
}

void i915_sched_node_fini(struct i915_sched_node *node)
{
        struct i915_dependency *dep, *tmp;

        spin_lock_irq(&schedule_lock);

        /*
         * Everyone we depended upon (the fences we wait to be signaled)
         * should retire before us and remove themselves from our list.
         * However, retirement is run independently on each timeline and
         * so we may be called out-of-order.
         */
        list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
                GEM_BUG_ON(!node_signaled(dep->signaler));
                GEM_BUG_ON(!list_empty(&dep->dfs_link));

                list_del(&dep->wait_link);
                if (dep->flags & I915_DEPENDENCY_ALLOC)
                        i915_dependency_free(dep);
        }

        /* Remove ourselves from everyone who depends upon us */
        list_for_each_entry_safe(dep, tmp, &node->waiters_list, wait_link) {
                GEM_BUG_ON(dep->signaler != node);
                GEM_BUG_ON(!list_empty(&dep->dfs_link));

                list_del(&dep->signal_link);
                if (dep->flags & I915_DEPENDENCY_ALLOC)
                        i915_dependency_free(dep);
        }

        spin_unlock_irq(&schedule_lock);
}

static void i915_global_scheduler_shrink(void)
{
        kmem_cache_shrink(global.slab_dependencies);
        kmem_cache_shrink(global.slab_priorities);
}

static void i915_global_scheduler_exit(void)
{
        kmem_cache_destroy(global.slab_dependencies);
        kmem_cache_destroy(global.slab_priorities);
}

static struct i915_global_scheduler global = { {
        .shrink = i915_global_scheduler_shrink,
        .exit = i915_global_scheduler_exit,
} };

int __init i915_global_scheduler_init(void)
{
        global.slab_dependencies = KMEM_CACHE(i915_dependency,
                                              SLAB_HWCACHE_ALIGN);
        if (!global.slab_dependencies)
                return -ENOMEM;

        global.slab_priorities = KMEM_CACHE(i915_priolist,
                                            SLAB_HWCACHE_ALIGN);
        if (!global.slab_priorities)
                goto err_priorities;

        i915_global_register(&global.base);
        return 0;

err_priorities:
        kmem_cache_destroy(global.slab_priorities);
        return -ENOMEM;
}