drm/i915: Disable semaphore busywaits on saturated systems

[linux.git] / drivers / gpu / drm / i915 / i915_request.c

/*
 * Copyright © 2008-2015 Intel Corporation
 *
 * 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 (including the next
 * paragraph) 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 AUTHORS OR COPYRIGHT HOLDERS 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.
 *
 */

#include <linux/dma-fence-array.h>
#include <linux/irq_work.h>
#include <linux/prefetch.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/sched/signal.h>

#include "i915_active.h"
#include "i915_drv.h"
#include "i915_globals.h"
#include "i915_reset.h"
#include "intel_pm.h"

struct execute_cb {
        struct list_head link;
        struct irq_work work;
        struct i915_sw_fence *fence;
};

static struct i915_global_request {
        struct i915_global base;
        struct kmem_cache *slab_requests;
        struct kmem_cache *slab_dependencies;
        struct kmem_cache *slab_execute_cbs;
} global;

static const char *i915_fence_get_driver_name(struct dma_fence *fence)
{
        return "i915";
}

static const char *i915_fence_get_timeline_name(struct dma_fence *fence)
{
        /*
         * The timeline struct (as part of the ppgtt underneath a context)
         * may be freed when the request is no longer in use by the GPU.
         * We could extend the life of a context to beyond that of all
         * fences, possibly keeping the hw resource around indefinitely,
         * or we just give them a false name. Since
         * dma_fence_ops.get_timeline_name is a debug feature, the occasional
         * lie seems justifiable.
         */
        if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
                return "signaled";

        return to_request(fence)->gem_context->name ?: "[i915]";
}

static bool i915_fence_signaled(struct dma_fence *fence)
{
        return i915_request_completed(to_request(fence));
}

static bool i915_fence_enable_signaling(struct dma_fence *fence)
{
        return i915_request_enable_breadcrumb(to_request(fence));
}

static signed long i915_fence_wait(struct dma_fence *fence,
                                   bool interruptible,
                                   signed long timeout)
{
        return i915_request_wait(to_request(fence),
                                 interruptible | I915_WAIT_PRIORITY,
                                 timeout);
}

static void i915_fence_release(struct dma_fence *fence)
{
        struct i915_request *rq = to_request(fence);

        /*
         * The request is put onto a RCU freelist (i.e. the address
         * is immediately reused), mark the fences as being freed now.
         * Otherwise the debugobjects for the fences are only marked as
         * freed when the slab cache itself is freed, and so we would get
         * caught trying to reuse dead objects.
         */
        i915_sw_fence_fini(&rq->submit);
        i915_sw_fence_fini(&rq->semaphore);

        kmem_cache_free(global.slab_requests, rq);
}

const struct dma_fence_ops i915_fence_ops = {
        .get_driver_name = i915_fence_get_driver_name,
        .get_timeline_name = i915_fence_get_timeline_name,
        .enable_signaling = i915_fence_enable_signaling,
        .signaled = i915_fence_signaled,
        .wait = i915_fence_wait,
        .release = i915_fence_release,
};

static inline void
i915_request_remove_from_client(struct i915_request *request)
{
        struct drm_i915_file_private *file_priv;

        file_priv = request->file_priv;
        if (!file_priv)
                return;

        spin_lock(&file_priv->mm.lock);
        if (request->file_priv) {
                list_del(&request->client_link);
                request->file_priv = NULL;
        }
        spin_unlock(&file_priv->mm.lock);
}

static void reserve_gt(struct drm_i915_private *i915)
{
        if (!i915->gt.active_requests++)
                i915_gem_unpark(i915);
}

static void unreserve_gt(struct drm_i915_private *i915)
{
        GEM_BUG_ON(!i915->gt.active_requests);
        if (!--i915->gt.active_requests)
                i915_gem_park(i915);
}

static void advance_ring(struct i915_request *request)
{
        struct intel_ring *ring = request->ring;
        unsigned int tail;

        /*
         * We know the GPU must have read the request to have
         * sent us the seqno + interrupt, so use the position
         * of tail of the request to update the last known position
         * of the GPU head.
         *
         * Note this requires that we are always called in request
         * completion order.
         */
        GEM_BUG_ON(!list_is_first(&request->ring_link, &ring->request_list));
        if (list_is_last(&request->ring_link, &ring->request_list)) {
                /*
                 * We may race here with execlists resubmitting this request
                 * as we retire it. The resubmission will move the ring->tail
                 * forwards (to request->wa_tail). We either read the
                 * current value that was written to hw, or the value that
                 * is just about to be. Either works, if we miss the last two
                 * noops - they are safe to be replayed on a reset.
                 */
                tail = READ_ONCE(request->tail);
                list_del(&ring->active_link);
        } else {
                tail = request->postfix;
        }
        list_del_init(&request->ring_link);

        ring->head = tail;
}

static void free_capture_list(struct i915_request *request)
{
        struct i915_capture_list *capture;

        capture = request->capture_list;
        while (capture) {
                struct i915_capture_list *next = capture->next;

                kfree(capture);
                capture = next;
        }
}

static void __retire_engine_request(struct intel_engine_cs *engine,
                                    struct i915_request *rq)
{
        GEM_TRACE("%s(%s) fence %llx:%lld, current %d\n",
                  __func__, engine->name,
                  rq->fence.context, rq->fence.seqno,
                  hwsp_seqno(rq));

        GEM_BUG_ON(!i915_request_completed(rq));

        local_irq_disable();

        spin_lock(&engine->timeline.lock);
        GEM_BUG_ON(!list_is_first(&rq->link, &engine->timeline.requests));
        list_del_init(&rq->link);
        spin_unlock(&engine->timeline.lock);

        spin_lock(&rq->lock);
        i915_request_mark_complete(rq);
        if (!i915_request_signaled(rq))
                dma_fence_signal_locked(&rq->fence);
        if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags))
                i915_request_cancel_breadcrumb(rq);
        if (rq->waitboost) {
                GEM_BUG_ON(!atomic_read(&rq->i915->gt_pm.rps.num_waiters));
                atomic_dec(&rq->i915->gt_pm.rps.num_waiters);
        }
        spin_unlock(&rq->lock);

        local_irq_enable();

        /*
         * The backing object for the context is done after switching to the
         * *next* context. Therefore we cannot retire the previous context until
         * the next context has already started running. However, since we
         * cannot take the required locks at i915_request_submit() we
         * defer the unpinning of the active context to now, retirement of
         * the subsequent request.
         */
        if (engine->last_retired_context)
                intel_context_unpin(engine->last_retired_context);
        engine->last_retired_context = rq->hw_context;
}

static void __retire_engine_upto(struct intel_engine_cs *engine,
                                 struct i915_request *rq)
{
        struct i915_request *tmp;

        if (list_empty(&rq->link))
                return;

        do {
                tmp = list_first_entry(&engine->timeline.requests,
                                       typeof(*tmp), link);

                GEM_BUG_ON(tmp->engine != engine);
                __retire_engine_request(engine, tmp);
        } while (tmp != rq);
}

static void i915_request_retire(struct i915_request *request)
{
        struct i915_active_request *active, *next;

        GEM_TRACE("%s fence %llx:%lld, current %d\n",
                  request->engine->name,
                  request->fence.context, request->fence.seqno,
                  hwsp_seqno(request));

        lockdep_assert_held(&request->i915->drm.struct_mutex);
        GEM_BUG_ON(!i915_sw_fence_signaled(&request->submit));
        GEM_BUG_ON(!i915_request_completed(request));

        trace_i915_request_retire(request);

        advance_ring(request);
        free_capture_list(request);

        /*
         * Walk through the active list, calling retire on each. This allows
         * objects to track their GPU activity and mark themselves as idle
         * when their *last* active request is completed (updating state
         * tracking lists for eviction, active references for GEM, etc).
         *
         * As the ->retire() may free the node, we decouple it first and
         * pass along the auxiliary information (to avoid dereferencing
         * the node after the callback).
         */
        list_for_each_entry_safe(active, next, &request->active_list, link) {
                /*
                 * In microbenchmarks or focusing upon time inside the kernel,
                 * we may spend an inordinate amount of time simply handling
                 * the retirement of requests and processing their callbacks.
                 * Of which, this loop itself is particularly hot due to the
                 * cache misses when jumping around the list of
                 * i915_active_request.  So we try to keep this loop as
                 * streamlined as possible and also prefetch the next
                 * i915_active_request to try and hide the likely cache miss.
                 */
                prefetchw(next);

                INIT_LIST_HEAD(&active->link);
                RCU_INIT_POINTER(active->request, NULL);

                active->retire(active, request);
        }

        i915_request_remove_from_client(request);

        intel_context_unpin(request->hw_context);

        __retire_engine_upto(request->engine, request);

        unreserve_gt(request->i915);

        i915_sched_node_fini(&request->sched);
        i915_request_put(request);
}

void i915_request_retire_upto(struct i915_request *rq)
{
        struct intel_ring *ring = rq->ring;
        struct i915_request *tmp;

        GEM_TRACE("%s fence %llx:%lld, current %d\n",
                  rq->engine->name,
                  rq->fence.context, rq->fence.seqno,
                  hwsp_seqno(rq));

        lockdep_assert_held(&rq->i915->drm.struct_mutex);
        GEM_BUG_ON(!i915_request_completed(rq));

        if (list_empty(&rq->ring_link))
                return;

        do {
                tmp = list_first_entry(&ring->request_list,
                                       typeof(*tmp), ring_link);

                i915_request_retire(tmp);
        } while (tmp != rq);
}

static void irq_execute_cb(struct irq_work *wrk)
{
        struct execute_cb *cb = container_of(wrk, typeof(*cb), work);

        i915_sw_fence_complete(cb->fence);
        kmem_cache_free(global.slab_execute_cbs, cb);
}

static void __notify_execute_cb(struct i915_request *rq)
{
        struct execute_cb *cb;

        lockdep_assert_held(&rq->lock);

        if (list_empty(&rq->execute_cb))
                return;

        list_for_each_entry(cb, &rq->execute_cb, link)
                irq_work_queue(&cb->work);

        /*
         * XXX Rollback on __i915_request_unsubmit()
         *
         * In the future, perhaps when we have an active time-slicing scheduler,
         * it will be interesting to unsubmit parallel execution and remove
         * busywaits from the GPU until their master is restarted. This is
         * quite hairy, we have to carefully rollback the fence and do a
         * preempt-to-idle cycle on the target engine, all the while the
         * master execute_cb may refire.
         */
        INIT_LIST_HEAD(&rq->execute_cb);
}

static int
i915_request_await_execution(struct i915_request *rq,
                             struct i915_request *signal,
                             gfp_t gfp)
{
        struct execute_cb *cb;

        if (i915_request_is_active(signal))
                return 0;

        cb = kmem_cache_alloc(global.slab_execute_cbs, gfp);
        if (!cb)
                return -ENOMEM;

        cb->fence = &rq->submit;
        i915_sw_fence_await(cb->fence);
        init_irq_work(&cb->work, irq_execute_cb);

        spin_lock_irq(&signal->lock);
        if (i915_request_is_active(signal)) {
                i915_sw_fence_complete(cb->fence);
                kmem_cache_free(global.slab_execute_cbs, cb);
        } else {
                list_add_tail(&cb->link, &signal->execute_cb);
        }
        spin_unlock_irq(&signal->lock);

        return 0;
}

static void move_to_timeline(struct i915_request *request,
                             struct i915_timeline *timeline)
{
        GEM_BUG_ON(request->timeline == &request->engine->timeline);
        lockdep_assert_held(&request->engine->timeline.lock);

        spin_lock(&request->timeline->lock);
        list_move_tail(&request->link, &timeline->requests);
        spin_unlock(&request->timeline->lock);
}

void __i915_request_submit(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;

        GEM_TRACE("%s fence %llx:%lld -> current %d\n",
                  engine->name,
                  request->fence.context, request->fence.seqno,
                  hwsp_seqno(request));

        GEM_BUG_ON(!irqs_disabled());
        lockdep_assert_held(&engine->timeline.lock);

        if (i915_gem_context_is_banned(request->gem_context))
                i915_request_skip(request, -EIO);

        /*
         * Are we using semaphores when the gpu is already saturated?
         *
         * Using semaphores incurs a cost in having the GPU poll a
         * memory location, busywaiting for it to change. The continual
         * memory reads can have a noticeable impact on the rest of the
         * system with the extra bus traffic, stalling the cpu as it too
         * tries to access memory across the bus (perf stat -e bus-cycles).
         *
         * If we installed a semaphore on this request and we only submit
         * the request after the signaler completed, that indicates the
         * system is overloaded and using semaphores at this time only
         * increases the amount of work we are doing. If so, we disable
         * further use of semaphores until we are idle again, whence we
         * optimistically try again.
         */
        if (request->sched.semaphores &&
            i915_sw_fence_signaled(&request->semaphore))
                request->hw_context->saturated |= request->sched.semaphores;

        /* We may be recursing from the signal callback of another i915 fence */
        spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);

        GEM_BUG_ON(test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));
        set_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags);

        if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
            !i915_request_enable_breadcrumb(request))
                intel_engine_queue_breadcrumbs(engine);

        __notify_execute_cb(request);

        spin_unlock(&request->lock);

        engine->emit_fini_breadcrumb(request,
                                     request->ring->vaddr + request->postfix);

        /* Transfer from per-context onto the global per-engine timeline */
        move_to_timeline(request, &engine->timeline);

        trace_i915_request_execute(request);
}

void i915_request_submit(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;
        unsigned long flags;

        /* Will be called from irq-context when using foreign fences. */
        spin_lock_irqsave(&engine->timeline.lock, flags);

        __i915_request_submit(request);

        spin_unlock_irqrestore(&engine->timeline.lock, flags);
}

void __i915_request_unsubmit(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;

        GEM_TRACE("%s fence %llx:%lld, current %d\n",
                  engine->name,
                  request->fence.context, request->fence.seqno,
                  hwsp_seqno(request));

        GEM_BUG_ON(!irqs_disabled());
        lockdep_assert_held(&engine->timeline.lock);

        /*
         * Only unwind in reverse order, required so that the per-context list
         * is kept in seqno/ring order.
         */

        /* We may be recursing from the signal callback of another i915 fence */
        spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);

        /*
         * 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); /* only internal */
        request->sched.attr.priority |= __NO_PREEMPTION;

        if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
                i915_request_cancel_breadcrumb(request);

        GEM_BUG_ON(!test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));
        clear_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags);

        spin_unlock(&request->lock);

        /* Transfer back from the global per-engine timeline to per-context */
        move_to_timeline(request, request->timeline);

        /*
         * We don't need to wake_up any waiters on request->execute, they
         * will get woken by any other event or us re-adding this request
         * to the engine timeline (__i915_request_submit()). The waiters
         * should be quite adapt at finding that the request now has a new
         * global_seqno to the one they went to sleep on.
         */
}

void i915_request_unsubmit(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;
        unsigned long flags;

        /* Will be called from irq-context when using foreign fences. */
        spin_lock_irqsave(&engine->timeline.lock, flags);

        __i915_request_unsubmit(request);

        spin_unlock_irqrestore(&engine->timeline.lock, flags);
}

static int __i915_sw_fence_call
submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
{
        struct i915_request *request =
                container_of(fence, typeof(*request), submit);

        switch (state) {
        case FENCE_COMPLETE:
                trace_i915_request_submit(request);
                /*
                 * We need to serialize use of the submit_request() callback
                 * with its hotplugging performed during an emergency
                 * i915_gem_set_wedged().  We use the RCU mechanism to mark the
                 * critical section in order to force i915_gem_set_wedged() to
                 * wait until the submit_request() is completed before
                 * proceeding.
                 */
                rcu_read_lock();
                request->engine->submit_request(request);
                rcu_read_unlock();
                break;

        case FENCE_FREE:
                i915_request_put(request);
                break;
        }

        return NOTIFY_DONE;
}

static int __i915_sw_fence_call
semaphore_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
{
        struct i915_request *request =
                container_of(fence, typeof(*request), semaphore);

        switch (state) {
        case FENCE_COMPLETE:
                /*
                 * We only check a small portion of our dependencies
                 * and so cannot guarantee that there remains no
                 * semaphore chain across all. Instead of opting
                 * for the full NOSEMAPHORE boost, we go for the
                 * smaller (but still preempting) boost of
                 * NEWCLIENT. This will be enough to boost over
                 * a busywaiting request (as that cannot be
                 * NEWCLIENT) without accidentally boosting
                 * a busywait over real work elsewhere.
                 */
                i915_schedule_bump_priority(request, I915_PRIORITY_NEWCLIENT);
                break;

        case FENCE_FREE:
                i915_request_put(request);
                break;
        }

        return NOTIFY_DONE;
}

static void ring_retire_requests(struct intel_ring *ring)
{
        struct i915_request *rq, *rn;

        list_for_each_entry_safe(rq, rn, &ring->request_list, ring_link) {
                if (!i915_request_completed(rq))
                        break;

                i915_request_retire(rq);
        }
}

static noinline struct i915_request *
i915_request_alloc_slow(struct intel_context *ce)
{
        struct intel_ring *ring = ce->ring;
        struct i915_request *rq;

        if (list_empty(&ring->request_list))
                goto out;

        /* Ratelimit ourselves to prevent oom from malicious clients */
        rq = list_last_entry(&ring->request_list, typeof(*rq), ring_link);
        cond_synchronize_rcu(rq->rcustate);

        /* Retire our old requests in the hope that we free some */
        ring_retire_requests(ring);

out:
        return kmem_cache_alloc(global.slab_requests, GFP_KERNEL);
}

/**
 * i915_request_alloc - allocate a request structure
 *
 * @engine: engine that we wish to issue the request on.
 * @ctx: context that the request will be associated with.
 *
 * Returns a pointer to the allocated request if successful,
 * or an error code if not.
 */
struct i915_request *
i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
{
        struct drm_i915_private *i915 = engine->i915;
        struct intel_context *ce;
        struct i915_timeline *tl;
        struct i915_request *rq;
        u32 seqno;
        int ret;

        lockdep_assert_held(&i915->drm.struct_mutex);

        /*
         * Preempt contexts are reserved for exclusive use to inject a
         * preemption context switch. They are never to be used for any trivial
         * request!
         */
        GEM_BUG_ON(ctx == i915->preempt_context);

        /*
         * ABI: Before userspace accesses the GPU (e.g. execbuffer), report
         * EIO if the GPU is already wedged.
         */
        ret = i915_terminally_wedged(i915);
        if (ret)
                return ERR_PTR(ret);

        /*
         * Pinning the contexts may generate requests in order to acquire
         * GGTT space, so do this first before we reserve a seqno for
         * ourselves.
         */
        ce = intel_context_pin(ctx, engine);
        if (IS_ERR(ce))
                return ERR_CAST(ce);

        reserve_gt(i915);
        mutex_lock(&ce->ring->timeline->mutex);

        /* Move our oldest request to the slab-cache (if not in use!) */
        rq = list_first_entry(&ce->ring->request_list, typeof(*rq), ring_link);
        if (!list_is_last(&rq->ring_link, &ce->ring->request_list) &&
            i915_request_completed(rq))
                i915_request_retire(rq);

        /*
         * Beware: Dragons be flying overhead.
         *
         * We use RCU to look up requests in flight. The lookups may
         * race with the request being allocated from the slab freelist.
         * That is the request we are writing to here, may be in the process
         * of being read by __i915_active_request_get_rcu(). As such,
         * we have to be very careful when overwriting the contents. During
         * the RCU lookup, we change chase the request->engine pointer,
         * read the request->global_seqno and increment the reference count.
         *
         * The reference count is incremented atomically. If it is zero,
         * the lookup knows the request is unallocated and complete. Otherwise,
         * it is either still in use, or has been reallocated and reset
         * with dma_fence_init(). This increment is safe for release as we
         * check that the request we have a reference to and matches the active
         * request.
         *
         * Before we increment the refcount, we chase the request->engine
         * pointer. We must not call kmem_cache_zalloc() or else we set
         * that pointer to NULL and cause a crash during the lookup. If
         * we see the request is completed (based on the value of the
         * old engine and seqno), the lookup is complete and reports NULL.
         * If we decide the request is not completed (new engine or seqno),
         * then we grab a reference and double check that it is still the
         * active request - which it won't be and restart the lookup.
         *
         * Do not use kmem_cache_zalloc() here!
         */
        rq = kmem_cache_alloc(global.slab_requests,
                              GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
        if (unlikely(!rq)) {
                rq = i915_request_alloc_slow(ce);
                if (!rq) {
                        ret = -ENOMEM;
                        goto err_unreserve;
                }
        }

        INIT_LIST_HEAD(&rq->active_list);
        INIT_LIST_HEAD(&rq->execute_cb);

        tl = ce->ring->timeline;
        ret = i915_timeline_get_seqno(tl, rq, &seqno);
        if (ret)
                goto err_free;

        rq->i915 = i915;
        rq->engine = engine;
        rq->gem_context = ctx;
        rq->hw_context = ce;
        rq->ring = ce->ring;
        rq->timeline = tl;
        GEM_BUG_ON(rq->timeline == &engine->timeline);
        rq->hwsp_seqno = tl->hwsp_seqno;
        rq->hwsp_cacheline = tl->hwsp_cacheline;
        rq->rcustate = get_state_synchronize_rcu(); /* acts as smp_mb() */

        spin_lock_init(&rq->lock);
        dma_fence_init(&rq->fence, &i915_fence_ops, &rq->lock,
                       tl->fence_context, seqno);

        /* We bump the ref for the fence chain */
        i915_sw_fence_init(&i915_request_get(rq)->submit, submit_notify);
        i915_sw_fence_init(&i915_request_get(rq)->semaphore, semaphore_notify);

        i915_sched_node_init(&rq->sched);

        /* No zalloc, must clear what we need by hand */
        rq->file_priv = NULL;
        rq->batch = NULL;
        rq->capture_list = NULL;
        rq->waitboost = false;

        /*
         * Reserve space in the ring buffer for all the commands required to
         * eventually emit this request. This is to guarantee that the
         * i915_request_add() call can't fail. Note that the reserve may need
         * to be redone if the request is not actually submitted straight
         * away, e.g. because a GPU scheduler has deferred it.
         *
         * Note that due to how we add reserved_space to intel_ring_begin()
         * we need to double our request to ensure that if we need to wrap
         * around inside i915_request_add() there is sufficient space at
         * the beginning of the ring as well.
         */
        rq->reserved_space = 2 * engine->emit_fini_breadcrumb_dw * sizeof(u32);

        /*
         * Record the position of the start of the request so that
         * should we detect the updated seqno part-way through the
         * GPU processing the request, we never over-estimate the
         * position of the head.
         */
        rq->head = rq->ring->emit;

        ret = engine->request_alloc(rq);
        if (ret)
                goto err_unwind;

        /* Keep a second pin for the dual retirement along engine and ring */
        __intel_context_pin(ce);

        rq->infix = rq->ring->emit; /* end of header; start of user payload */

        /* Check that we didn't interrupt ourselves with a new request */
        lockdep_assert_held(&rq->timeline->mutex);
        GEM_BUG_ON(rq->timeline->seqno != rq->fence.seqno);
        rq->cookie = lockdep_pin_lock(&rq->timeline->mutex);

        return rq;

err_unwind:
        ce->ring->emit = rq->head;

        /* Make sure we didn't add ourselves to external state before freeing */
        GEM_BUG_ON(!list_empty(&rq->active_list));
        GEM_BUG_ON(!list_empty(&rq->sched.signalers_list));
        GEM_BUG_ON(!list_empty(&rq->sched.waiters_list));

err_free:
        kmem_cache_free(global.slab_requests, rq);
err_unreserve:
        mutex_unlock(&ce->ring->timeline->mutex);
        unreserve_gt(i915);
        intel_context_unpin(ce);
        return ERR_PTR(ret);
}

static int
i915_request_await_start(struct i915_request *rq, struct i915_request *signal)
{
        if (list_is_first(&signal->ring_link, &signal->ring->request_list))
                return 0;

        signal = list_prev_entry(signal, ring_link);
        if (i915_timeline_sync_is_later(rq->timeline, &signal->fence))
                return 0;

        return i915_sw_fence_await_dma_fence(&rq->submit,
                                             &signal->fence, 0,
                                             I915_FENCE_GFP);
}

static intel_engine_mask_t
already_busywaiting(struct i915_request *rq)
{
        /*
         * Polling a semaphore causes bus traffic, delaying other users of
         * both the GPU and CPU. We want to limit the impact on others,
         * while taking advantage of early submission to reduce GPU
         * latency. Therefore we restrict ourselves to not using more
         * than one semaphore from each source, and not using a semaphore
         * if we have detected the engine is saturated (i.e. would not be
         * submitted early and cause bus traffic reading an already passed
         * semaphore).
         *
         * See the are-we-too-late? check in __i915_request_submit().
         */
        return rq->sched.semaphores | rq->hw_context->saturated;
}

static int
emit_semaphore_wait(struct i915_request *to,
                    struct i915_request *from,
                    gfp_t gfp)
{
        u32 hwsp_offset;
        u32 *cs;
        int err;

        GEM_BUG_ON(!from->timeline->has_initial_breadcrumb);
        GEM_BUG_ON(INTEL_GEN(to->i915) < 8);

        /* Just emit the first semaphore we see as request space is limited. */
        if (already_busywaiting(to) & from->engine->mask)
                return i915_sw_fence_await_dma_fence(&to->submit,
                                                     &from->fence, 0,
                                                     I915_FENCE_GFP);

        err = i915_request_await_start(to, from);
        if (err < 0)
                return err;

        err = i915_sw_fence_await_dma_fence(&to->semaphore,
                                            &from->fence, 0,
                                            I915_FENCE_GFP);
        if (err < 0)
                return err;

        /* We need to pin the signaler's HWSP until we are finished reading. */
        err = i915_timeline_read_hwsp(from, to, &hwsp_offset);
        if (err)
                return err;

        /* Only submit our spinner after the signaler is running! */
        err = i915_request_await_execution(to, from, gfp);
        if (err)
                return err;

        cs = intel_ring_begin(to, 4);
        if (IS_ERR(cs))
                return PTR_ERR(cs);

        /*
         * Using greater-than-or-equal here means we have to worry
         * about seqno wraparound. To side step that issue, we swap
         * the timeline HWSP upon wrapping, so that everyone listening
         * for the old (pre-wrap) values do not see the much smaller
         * (post-wrap) values than they were expecting (and so wait
         * forever).
         */
        *cs++ = MI_SEMAPHORE_WAIT |
                MI_SEMAPHORE_GLOBAL_GTT |
                MI_SEMAPHORE_POLL |
                MI_SEMAPHORE_SAD_GTE_SDD;
        *cs++ = from->fence.seqno;
        *cs++ = hwsp_offset;
        *cs++ = 0;

        intel_ring_advance(to, cs);
        to->sched.semaphores |= from->engine->mask;
        to->sched.flags |= I915_SCHED_HAS_SEMAPHORE_CHAIN;
        return 0;
}

static int
i915_request_await_request(struct i915_request *to, struct i915_request *from)
{
        int ret;

        GEM_BUG_ON(to == from);
        GEM_BUG_ON(to->timeline == from->timeline);

        if (i915_request_completed(from))
                return 0;

        if (to->engine->schedule) {
                ret = i915_sched_node_add_dependency(&to->sched, &from->sched);
                if (ret < 0)
                        return ret;
        }

        if (to->engine == from->engine) {
                ret = i915_sw_fence_await_sw_fence_gfp(&to->submit,
                                                       &from->submit,
                                                       I915_FENCE_GFP);
        } else if (intel_engine_has_semaphores(to->engine) &&
                   to->gem_context->sched.priority >= I915_PRIORITY_NORMAL) {
                ret = emit_semaphore_wait(to, from, I915_FENCE_GFP);
        } else {
                ret = i915_sw_fence_await_dma_fence(&to->submit,
                                                    &from->fence, 0,
                                                    I915_FENCE_GFP);
        }

        return ret < 0 ? ret : 0;
}

int
i915_request_await_dma_fence(struct i915_request *rq, struct dma_fence *fence)
{
        struct dma_fence **child = &fence;
        unsigned int nchild = 1;
        int ret;

        /*
         * Note that if the fence-array was created in signal-on-any mode,
         * we should *not* decompose it into its individual fences. However,
         * we don't currently store which mode the fence-array is operating
         * in. Fortunately, the only user of signal-on-any is private to
         * amdgpu and we should not see any incoming fence-array from
         * sync-file being in signal-on-any mode.
         */
        if (dma_fence_is_array(fence)) {
                struct dma_fence_array *array = to_dma_fence_array(fence);

                child = array->fences;
                nchild = array->num_fences;
                GEM_BUG_ON(!nchild);
        }

        do {
                fence = *child++;
                if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
                        continue;

                /*
                 * Requests on the same timeline are explicitly ordered, along
                 * with their dependencies, by i915_request_add() which ensures
                 * that requests are submitted in-order through each ring.
                 */
                if (fence->context == rq->fence.context)
                        continue;

                /* Squash repeated waits to the same timelines */
                if (fence->context != rq->i915->mm.unordered_timeline &&
                    i915_timeline_sync_is_later(rq->timeline, fence))
                        continue;

                if (dma_fence_is_i915(fence))
                        ret = i915_request_await_request(rq, to_request(fence));
                else
                        ret = i915_sw_fence_await_dma_fence(&rq->submit, fence,
                                                            I915_FENCE_TIMEOUT,
                                                            I915_FENCE_GFP);
                if (ret < 0)
                        return ret;

                /* Record the latest fence used against each timeline */
                if (fence->context != rq->i915->mm.unordered_timeline)
                        i915_timeline_sync_set(rq->timeline, fence);
        } while (--nchild);

        return 0;
}

/**
 * i915_request_await_object - set this request to (async) wait upon a bo
 * @to: request we are wishing to use
 * @obj: object which may be in use on another ring.
 * @write: whether the wait is on behalf of a writer
 *
 * This code is meant to abstract object synchronization with the GPU.
 * Conceptually we serialise writes between engines inside the GPU.
 * We only allow one engine to write into a buffer at any time, but
 * multiple readers. To ensure each has a coherent view of memory, we must:
 *
 * - If there is an outstanding write request to the object, the new
 *   request must wait for it to complete (either CPU or in hw, requests
 *   on the same ring will be naturally ordered).
 *
 * - If we are a write request (pending_write_domain is set), the new
 *   request must wait for outstanding read requests to complete.
 *
 * Returns 0 if successful, else propagates up the lower layer error.
 */
int
i915_request_await_object(struct i915_request *to,
                          struct drm_i915_gem_object *obj,
                          bool write)
{
        struct dma_fence *excl;
        int ret = 0;

        if (write) {
                struct dma_fence **shared;
                unsigned int count, i;

                ret = reservation_object_get_fences_rcu(obj->resv,
                                                        &excl, &count, &shared);
                if (ret)
                        return ret;

                for (i = 0; i < count; i++) {
                        ret = i915_request_await_dma_fence(to, shared[i]);
                        if (ret)
                                break;

                        dma_fence_put(shared[i]);
                }

                for (; i < count; i++)
                        dma_fence_put(shared[i]);
                kfree(shared);
        } else {
                excl = reservation_object_get_excl_rcu(obj->resv);
        }

        if (excl) {
                if (ret == 0)
                        ret = i915_request_await_dma_fence(to, excl);

                dma_fence_put(excl);
        }

        return ret;
}

void i915_request_skip(struct i915_request *rq, int error)
{
        void *vaddr = rq->ring->vaddr;
        u32 head;

        GEM_BUG_ON(!IS_ERR_VALUE((long)error));
        dma_fence_set_error(&rq->fence, error);

        /*
         * As this request likely depends on state from the lost
         * context, clear out all the user operations leaving the
         * breadcrumb at the end (so we get the fence notifications).
         */
        head = rq->infix;
        if (rq->postfix < head) {
                memset(vaddr + head, 0, rq->ring->size - head);
                head = 0;
        }
        memset(vaddr + head, 0, rq->postfix - head);
}

static struct i915_request *
__i915_request_add_to_timeline(struct i915_request *rq)
{
        struct i915_timeline *timeline = rq->timeline;
        struct i915_request *prev;

        /*
         * Dependency tracking and request ordering along the timeline
         * is special cased so that we can eliminate redundant ordering
         * operations while building the request (we know that the timeline
         * itself is ordered, and here we guarantee it).
         *
         * As we know we will need to emit tracking along the timeline,
         * we embed the hooks into our request struct -- at the cost of
         * having to have specialised no-allocation interfaces (which will
         * be beneficial elsewhere).
         *
         * A second benefit to open-coding i915_request_await_request is
         * that we can apply a slight variant of the rules specialised
         * for timelines that jump between engines (such as virtual engines).
         * If we consider the case of virtual engine, we must emit a dma-fence
         * to prevent scheduling of the second request until the first is
         * complete (to maximise our greedy late load balancing) and this
         * precludes optimising to use semaphores serialisation of a single
         * timeline across engines.
         */
        prev = i915_active_request_raw(&timeline->last_request,
                                       &rq->i915->drm.struct_mutex);
        if (prev && !i915_request_completed(prev)) {
                if (is_power_of_2(prev->engine->mask | rq->engine->mask))
                        i915_sw_fence_await_sw_fence(&rq->submit,
                                                     &prev->submit,
                                                     &rq->submitq);
                else
                        __i915_sw_fence_await_dma_fence(&rq->submit,
                                                        &prev->fence,
                                                        &rq->dmaq);
                if (rq->engine->schedule)
                        __i915_sched_node_add_dependency(&rq->sched,
                                                         &prev->sched,
                                                         &rq->dep,
                                                         0);
        }

        spin_lock_irq(&timeline->lock);
        list_add_tail(&rq->link, &timeline->requests);
        spin_unlock_irq(&timeline->lock);

        GEM_BUG_ON(timeline->seqno != rq->fence.seqno);
        __i915_active_request_set(&timeline->last_request, rq);

        return prev;
}

/*
 * NB: This function is not allowed to fail. Doing so would mean the the
 * request is not being tracked for completion but the work itself is
 * going to happen on the hardware. This would be a Bad Thing(tm).
 */
void i915_request_add(struct i915_request *request)
{
        struct intel_engine_cs *engine = request->engine;
        struct i915_timeline *timeline = request->timeline;
        struct intel_ring *ring = request->ring;
        struct i915_request *prev;
        u32 *cs;

        GEM_TRACE("%s fence %llx:%lld\n",
                  engine->name, request->fence.context, request->fence.seqno);

        lockdep_assert_held(&request->timeline->mutex);
        lockdep_unpin_lock(&request->timeline->mutex, request->cookie);

        trace_i915_request_add(request);

        /*
         * Make sure that no request gazumped us - if it was allocated after
         * our i915_request_alloc() and called __i915_request_add() before
         * us, the timeline will hold its seqno which is later than ours.
         */
        GEM_BUG_ON(timeline->seqno != request->fence.seqno);

        /*
         * To ensure that this call will not fail, space for its emissions
         * should already have been reserved in the ring buffer. Let the ring
         * know that it is time to use that space up.
         */
        GEM_BUG_ON(request->reserved_space > request->ring->space);
        request->reserved_space = 0;

        /*
         * Record the position of the start of the breadcrumb so that
         * should we detect the updated seqno part-way through the
         * GPU processing the request, we never over-estimate the
         * position of the ring's HEAD.
         */
        cs = intel_ring_begin(request, engine->emit_fini_breadcrumb_dw);
        GEM_BUG_ON(IS_ERR(cs));
        request->postfix = intel_ring_offset(request, cs);

        prev = __i915_request_add_to_timeline(request);

        list_add_tail(&request->ring_link, &ring->request_list);
        if (list_is_first(&request->ring_link, &ring->request_list))
                list_add(&ring->active_link, &request->i915->gt.active_rings);
        request->i915->gt.active_engines |= request->engine->mask;
        request->emitted_jiffies = jiffies;

        /*
         * Let the backend know a new request has arrived that may need
         * to adjust the existing execution schedule due to a high priority
         * request - i.e. we may want to preempt the current request in order
         * to run a high priority dependency chain *before* we can execute this
         * request.
         *
         * This is called before the request is ready to run so that we can
         * decide whether to preempt the entire chain so that it is ready to
         * run at the earliest possible convenience.
         */
        local_bh_disable();
        i915_sw_fence_commit(&request->semaphore);
        rcu_read_lock(); /* RCU serialisation for set-wedged protection */
        if (engine->schedule) {
                struct i915_sched_attr attr = request->gem_context->sched;

                /*
                 * Boost actual workloads past semaphores!
                 *
                 * With semaphores we spin on one engine waiting for another,
                 * simply to reduce the latency of starting our work when
                 * the signaler completes. However, if there is any other
                 * work that we could be doing on this engine instead, that
                 * is better utilisation and will reduce the overall duration
                 * of the current work. To avoid PI boosting a semaphore
                 * far in the distance past over useful work, we keep a history
                 * of any semaphore use along our dependency chain.
                 */
                if (!(request->sched.flags & I915_SCHED_HAS_SEMAPHORE_CHAIN))
                        attr.priority |= I915_PRIORITY_NOSEMAPHORE;

                /*
                 * Boost priorities to new clients (new request flows).
                 *
                 * Allow interactive/synchronous clients to jump ahead of
                 * the bulk clients. (FQ_CODEL)
                 */
                if (list_empty(&request->sched.signalers_list))
                        attr.priority |= I915_PRIORITY_NEWCLIENT;

                engine->schedule(request, &attr);
        }
        rcu_read_unlock();
        i915_sw_fence_commit(&request->submit);
        local_bh_enable(); /* Kick the execlists tasklet if just scheduled */

        /*
         * In typical scenarios, we do not expect the previous request on
         * the timeline to be still tracked by timeline->last_request if it
         * has been completed. If the completed request is still here, that
         * implies that request retirement is a long way behind submission,
         * suggesting that we haven't been retiring frequently enough from
         * the combination of retire-before-alloc, waiters and the background
         * retirement worker. So if the last request on this timeline was
         * already completed, do a catch up pass, flushing the retirement queue
         * up to this client. Since we have now moved the heaviest operations
         * during retirement onto secondary workers, such as freeing objects
         * or contexts, retiring a bunch of requests is mostly list management
         * (and cache misses), and so we should not be overly penalizing this
         * client by performing excess work, though we may still performing
         * work on behalf of others -- but instead we should benefit from
         * improved resource management. (Well, that's the theory at least.)
         */
        if (prev && i915_request_completed(prev))
                i915_request_retire_upto(prev);

        mutex_unlock(&request->timeline->mutex);
}

static unsigned long local_clock_us(unsigned int *cpu)
{
        unsigned long t;

        /*
         * Cheaply and approximately convert from nanoseconds to microseconds.
         * The result and subsequent calculations are also defined in the same
         * approximate microseconds units. The principal source of timing
         * error here is from the simple truncation.
         *
         * Note that local_clock() is only defined wrt to the current CPU;
         * the comparisons are no longer valid if we switch CPUs. Instead of
         * blocking preemption for the entire busywait, we can detect the CPU
         * switch and use that as indicator of system load and a reason to
         * stop busywaiting, see busywait_stop().
         */
        *cpu = get_cpu();
        t = local_clock() >> 10;
        put_cpu();

        return t;
}

static bool busywait_stop(unsigned long timeout, unsigned int cpu)
{
        unsigned int this_cpu;

        if (time_after(local_clock_us(&this_cpu), timeout))
                return true;

        return this_cpu != cpu;
}

static bool __i915_spin_request(const struct i915_request * const rq,
                                int state, unsigned long timeout_us)
{
        unsigned int cpu;

        /*
         * Only wait for the request if we know it is likely to complete.
         *
         * We don't track the timestamps around requests, nor the average
         * request length, so we do not have a good indicator that this
         * request will complete within the timeout. What we do know is the
         * order in which requests are executed by the context and so we can
         * tell if the request has been started. If the request is not even
         * running yet, it is a fair assumption that it will not complete
         * within our relatively short timeout.
         */
        if (!i915_request_is_running(rq))
                return false;

        /*
         * When waiting for high frequency requests, e.g. during synchronous
         * rendering split between the CPU and GPU, the finite amount of time
         * required to set up the irq and wait upon it limits the response
         * rate. By busywaiting on the request completion for a short while we
         * can service the high frequency waits as quick as possible. However,
         * if it is a slow request, we want to sleep as quickly as possible.
         * The tradeoff between waiting and sleeping is roughly the time it
         * takes to sleep on a request, on the order of a microsecond.
         */

        timeout_us += local_clock_us(&cpu);
        do {
                if (i915_request_completed(rq))
                        return true;

                if (signal_pending_state(state, current))
                        break;

                if (busywait_stop(timeout_us, cpu))
                        break;

                cpu_relax();
        } while (!need_resched());

        return false;
}

struct request_wait {
        struct dma_fence_cb cb;
        struct task_struct *tsk;
};

static void request_wait_wake(struct dma_fence *fence, struct dma_fence_cb *cb)
{
        struct request_wait *wait = container_of(cb, typeof(*wait), cb);

        wake_up_process(wait->tsk);
}

/**
 * i915_request_wait - wait until execution of request has finished
 * @rq: the request to wait upon
 * @flags: how to wait
 * @timeout: how long to wait in jiffies
 *
 * i915_request_wait() waits for the request to be completed, for a
 * maximum of @timeout jiffies (with MAX_SCHEDULE_TIMEOUT implying an
 * unbounded wait).
 *
 * If the caller holds the struct_mutex, the caller must pass I915_WAIT_LOCKED
 * in via the flags, and vice versa if the struct_mutex is not held, the caller
 * must not specify that the wait is locked.
 *
 * Returns the remaining time (in jiffies) if the request completed, which may
 * be zero or -ETIME if the request is unfinished after the timeout expires.
 * May return -EINTR is called with I915_WAIT_INTERRUPTIBLE and a signal is
 * pending before the request completes.
 */
long i915_request_wait(struct i915_request *rq,
                       unsigned int flags,
                       long timeout)
{
        const int state = flags & I915_WAIT_INTERRUPTIBLE ?
                TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
        struct request_wait wait;

        might_sleep();
        GEM_BUG_ON(timeout < 0);

        if (i915_request_completed(rq))
                return timeout;

        if (!timeout)
                return -ETIME;

        trace_i915_request_wait_begin(rq, flags);

        /* Optimistic short spin before touching IRQs */
        if (__i915_spin_request(rq, state, 5))
                goto out;

        /*
         * This client is about to stall waiting for the GPU. In many cases
         * this is undesirable and limits the throughput of the system, as
         * many clients cannot continue processing user input/output whilst
         * blocked. RPS autotuning may take tens of milliseconds to respond
         * to the GPU load and thus incurs additional latency for the client.
         * We can circumvent that by promoting the GPU frequency to maximum
         * before we sleep. This makes the GPU throttle up much more quickly
         * (good for benchmarks and user experience, e.g. window animations),
         * but at a cost of spending more power processing the workload
         * (bad for battery).
         */
        if (flags & I915_WAIT_PRIORITY) {
                if (!i915_request_started(rq) && INTEL_GEN(rq->i915) >= 6)
                        gen6_rps_boost(rq);
                local_bh_disable(); /* suspend tasklets for reprioritisation */
                i915_schedule_bump_priority(rq, I915_PRIORITY_WAIT);
                local_bh_enable(); /* kick tasklets en masse */
        }

        wait.tsk = current;
        if (dma_fence_add_callback(&rq->fence, &wait.cb, request_wait_wake))
                goto out;

        for (;;) {
                set_current_state(state);

                if (i915_request_completed(rq))
                        break;

                if (signal_pending_state(state, current)) {
                        timeout = -ERESTARTSYS;
                        break;
                }

                if (!timeout) {
                        timeout = -ETIME;
                        break;
                }

                timeout = io_schedule_timeout(timeout);
        }
        __set_current_state(TASK_RUNNING);

        dma_fence_remove_callback(&rq->fence, &wait.cb);

out:
        trace_i915_request_wait_end(rq);
        return timeout;
}

void i915_retire_requests(struct drm_i915_private *i915)
{
        struct intel_ring *ring, *tmp;

        lockdep_assert_held(&i915->drm.struct_mutex);

        if (!i915->gt.active_requests)
                return;

        list_for_each_entry_safe(ring, tmp,
                                 &i915->gt.active_rings, active_link) {
                intel_ring_get(ring); /* last rq holds reference! */
                ring_retire_requests(ring);
                intel_ring_put(ring);
        }
}

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftests/mock_request.c"
#include "selftests/i915_request.c"
#endif

static void i915_global_request_shrink(void)
{
        kmem_cache_shrink(global.slab_dependencies);
        kmem_cache_shrink(global.slab_execute_cbs);
        kmem_cache_shrink(global.slab_requests);
}

static void i915_global_request_exit(void)
{
        kmem_cache_destroy(global.slab_dependencies);
        kmem_cache_destroy(global.slab_execute_cbs);
        kmem_cache_destroy(global.slab_requests);
}

static struct i915_global_request global = { {
        .shrink = i915_global_request_shrink,
        .exit = i915_global_request_exit,
} };

int __init i915_global_request_init(void)
{
        global.slab_requests = KMEM_CACHE(i915_request,
                                          SLAB_HWCACHE_ALIGN |
                                          SLAB_RECLAIM_ACCOUNT |
                                          SLAB_TYPESAFE_BY_RCU);
        if (!global.slab_requests)
                return -ENOMEM;

        global.slab_execute_cbs = KMEM_CACHE(execute_cb,
                                             SLAB_HWCACHE_ALIGN |
                                             SLAB_RECLAIM_ACCOUNT |
                                             SLAB_TYPESAFE_BY_RCU);
        if (!global.slab_execute_cbs)
                goto err_requests;

        global.slab_dependencies = KMEM_CACHE(i915_dependency,
                                              SLAB_HWCACHE_ALIGN |
                                              SLAB_RECLAIM_ACCOUNT);
        if (!global.slab_dependencies)
                goto err_execute_cbs;

        i915_global_register(&global.base);
        return 0;

err_execute_cbs:
        kmem_cache_destroy(global.slab_execute_cbs);
err_requests:
        kmem_cache_destroy(global.slab_requests);
        return -ENOMEM;
}