Re: [PATCH 1/8] drm/i915: Move priolist to new i915_sched_engine object

[Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>]

On 6/8/2021 12:17 PM, Matthew Brost wrote:
> Introduce i915_sched_engine object which is lower level data structure
> that i915_scheduler / generic code can operate on without touching
> execlist specific structures. This allows additional submission backends
> to be added without breaking the layering.
>
> This is a bit of detour to integrating the i915 with the DRM scheduler
> but this object will still exist when the DRM scheduler lands in the
> i915. It will however look a bit different. It will encapsulate the
> drm_gpu_scheduler object plus and common variables (to the backends)
> related to scheduling. Regardless this is a step in the right direction.

I think this needs some more explanation on how we plan to use this 
structure within i915, otherwise some implementation choices are 
unclear. E.g. i915_sched_engine_get() is unused in this patch and the 
whole kref logic only makes sense when you consider that with the GuC 
submission back-end we plan to point multiple engine_cs to the same 
sched_engine, so this needs to be explained.

> This patch starts the aforementioned transition by moving the priolist
> into the i915_sched_engine object.
>
> v3:
>   (Jason Ekstrand)
>    Update comment next to intel_engine_cs.virtual
>    Add kernel doc
>   (Checkpatch)
>    Fix double the in commit message
>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> ---
>   Documentation/gpu/i915.rst                    |  5 ++
>   drivers/gpu/drm/i915/gt/intel_engine_cs.c     | 14 +++-
>   drivers/gpu/drm/i915/gt/intel_engine_pm.c     |  4 +-
>   drivers/gpu/drm/i915/gt/intel_engine_types.h  | 32 ++------
>   .../drm/i915/gt/intel_execlists_submission.c  | 81 +++++++++++--------
>   drivers/gpu/drm/i915/gt/mock_engine.c         |  9 ++-
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 19 ++---
>   drivers/gpu/drm/i915/i915_scheduler.c         | 51 +++++++++---
>   drivers/gpu/drm/i915/i915_scheduler.h         | 18 +++++
>   drivers/gpu/drm/i915/i915_scheduler_types.h   | 47 +++++++++++
>   10 files changed, 190 insertions(+), 90 deletions(-)
>
> diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst
> index 42ce0196930a..1d5ce5676d35 100644
> --- a/Documentation/gpu/i915.rst
> +++ b/Documentation/gpu/i915.rst
> @@ -425,6 +425,11 @@ User Batchbuffer Execution
>   .. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
>      :doc: User command execution
>   
> +Scheduling
> +----------
> +.. kernel-doc:: drivers/gpu/drm/i915/i915_scheduler_types.h
> +   :functions: i915_sched_engine
> +
>   Logical Rings, Logical Ring Contexts and Execlists
>   --------------------------------------------------
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 9ceddfbb1687..49d44c3ac055 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -585,9 +585,6 @@ void intel_engine_init_execlists(struct intel_engine_cs *engine)
>   	memset(execlists->pending, 0, sizeof(execlists->pending));
>   	execlists->active =
>   		memset(execlists->inflight, 0, sizeof(execlists->inflight));
> -
> -	execlists->queue_priority_hint = INT_MIN;
> -	execlists->queue = RB_ROOT_CACHED;
>   }
>   
>   static void cleanup_status_page(struct intel_engine_cs *engine)
> @@ -714,6 +711,12 @@ static int engine_setup_common(struct intel_engine_cs *engine)
>   		goto err_status;
>   	}
>   
> +	engine->sched_engine = i915_sched_engine_create(ENGINE_PHYSICAL);
> +	if (!engine->sched_engine) {
> +		err = -ENOMEM;
> +		goto err_sched_engine;
> +	}
> +
>   	err = intel_engine_init_cmd_parser(engine);
>   	if (err)
>   		goto err_cmd_parser;
> @@ -737,6 +740,8 @@ static int engine_setup_common(struct intel_engine_cs *engine)
>   	return 0;
>   
>   err_cmd_parser:
> +	i915_sched_engine_put(engine->sched_engine);
> +err_sched_engine:
>   	intel_breadcrumbs_free(engine->breadcrumbs);
>   err_status:
>   	cleanup_status_page(engine);
> @@ -960,6 +965,7 @@ void intel_engine_cleanup_common(struct intel_engine_cs *engine)
>   	GEM_BUG_ON(!list_empty(&engine->active.requests));
>   	tasklet_kill(&engine->execlists.tasklet); /* flush the callback */
>   
> +	i915_sched_engine_put(engine->sched_engine);
>   	intel_breadcrumbs_free(engine->breadcrumbs);
>   
>   	intel_engine_fini_retire(engine);
> @@ -1283,7 +1289,7 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
>   	intel_engine_flush_submission(engine);
>   
>   	/* ELSP is empty, but there are ready requests? E.g. after reset */
> -	if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root))
> +	if (!RB_EMPTY_ROOT(&engine->sched_engine->queue.rb_root))
>   		return false;
>   
>   	/* Ring stopped? */
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> index 47f4397095e5..b6a00dd72808 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
> @@ -275,12 +275,12 @@ static int __engine_park(struct intel_wakeref *wf)
>   	intel_breadcrumbs_park(engine->breadcrumbs);
>   
>   	/* Must be reset upon idling, or we may miss the busy wakeup. */
> -	GEM_BUG_ON(engine->execlists.queue_priority_hint != INT_MIN);
> +	GEM_BUG_ON(engine->sched_engine->queue_priority_hint != INT_MIN);
>   
>   	if (engine->park)
>   		engine->park(engine);
>   
> -	engine->execlists.no_priolist = false;
> +	engine->sched_engine->no_priolist = false;
>   
>   	/* While gt calls i915_vma_parked(), we have to break the lock cycle */
>   	intel_gt_pm_put_async(engine->gt);
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index e113f93b3274..e41a9c3f9269 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -59,6 +59,7 @@ struct drm_i915_reg_table;
>   struct i915_gem_context;
>   struct i915_request;
>   struct i915_sched_attr;
> +struct i915_sched_engine;
>   struct intel_gt;
>   struct intel_ring;
>   struct intel_uncore;
> @@ -152,11 +153,6 @@ struct intel_engine_execlists {
>   	 */
>   	struct timer_list preempt;
>   
> -	/**
> -	 * @default_priolist: priority list for I915_PRIORITY_NORMAL
> -	 */
> -	struct i915_priolist default_priolist;
> -
>   	/**
>   	 * @ccid: identifier for contexts submitted to this engine
>   	 */
> @@ -191,11 +187,6 @@ struct intel_engine_execlists {
>   	 */
>   	u32 reset_ccid;
>   
> -	/**
> -	 * @no_priolist: priority lists disabled
> -	 */
> -	bool no_priolist;
> -
>   	/**
>   	 * @submit_reg: gen-specific execlist submission register
>   	 * set to the ExecList Submission Port (elsp) register pre-Gen11 and to
> @@ -238,23 +229,10 @@ struct intel_engine_execlists {
>   	unsigned int port_mask;
>   
>   	/**
> -	 * @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.
> +	 * @virtual: Queue of requets on a virtual engine, sorted by priority.
> +	 * Each RB entry is a struct i915_priolist containing a list of requests
> +	 * of the same priority.
>   	 */
> -	int queue_priority_hint;
> -
> -	/**
> -	 * @queue: queue of requests, in priority lists
> -	 */
> -	struct rb_root_cached queue;
>   	struct rb_root_cached virtual;
>   
>   	/**
> @@ -332,6 +310,8 @@ struct intel_engine_cs {
>   		struct list_head hold; /* ready requests, but on hold */
>   	} active;
>   
> +	struct i915_sched_engine *sched_engine;
> +
>   	/* keep a request in reserve for a [pm] barrier under oom */
>   	struct i915_request *request_pool;
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index fc77592d88a9..4f759559a792 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -273,11 +273,11 @@ static int effective_prio(const struct i915_request *rq)
>   	return prio;
>   }
>   
> -static int queue_prio(const struct intel_engine_execlists *execlists)
> +static int queue_prio(const struct i915_sched_engine *sched_engine)
>   {
>   	struct rb_node *rb;
>   
> -	rb = rb_first_cached(&execlists->queue);
> +	rb = rb_first_cached(&sched_engine->queue);
>   	if (!rb)
>   		return INT_MIN;
>   
> @@ -318,7 +318,7 @@ static bool need_preempt(const struct intel_engine_cs *engine,
>   	 * to preserve FIFO ordering of dependencies.
>   	 */
>   	last_prio = max(effective_prio(rq), I915_PRIORITY_NORMAL - 1);
> -	if (engine->execlists.queue_priority_hint <= last_prio)
> +	if (engine->sched_engine->queue_priority_hint <= last_prio)
>   		return false;
>   
>   	/*
> @@ -340,7 +340,7 @@ static bool need_preempt(const struct intel_engine_cs *engine,
>   	 * context, it's priority would not exceed ELSP[0] aka last_prio.
>   	 */
>   	return max(virtual_prio(&engine->execlists),
> -		   queue_prio(&engine->execlists)) > last_prio;
> +		   queue_prio(engine->sched_engine)) > last_prio;
>   }
>   
>   __maybe_unused static bool
> @@ -384,7 +384,7 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
>   			prio = rq_prio(rq);
>   			pl = i915_sched_lookup_priolist(engine, prio);
>   		}
> -		GEM_BUG_ON(RB_EMPTY_ROOT(&engine->execlists.queue.rb_root));
> +		GEM_BUG_ON(RB_EMPTY_ROOT(&engine->sched_engine->queue.rb_root));
>   
>   		list_move(&rq->sched.link, pl);
>   		set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> @@ -1139,7 +1139,7 @@ static bool needs_timeslice(const struct intel_engine_cs *engine,
>   	}
>   
>   	/* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */
> -	if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)) {
> +	if (!RB_EMPTY_ROOT(&engine->sched_engine->queue.rb_root)) {
>   		ENGINE_TRACE(engine, "timeslice required for queue\n");
>   		return true;
>   	}
> @@ -1236,6 +1236,7 @@ static bool completed(const struct i915_request *rq)
>   static void execlists_dequeue(struct intel_engine_cs *engine)
>   {
>   	struct intel_engine_execlists * const execlists = &engine->execlists;
> +	struct i915_sched_engine * const sched_engine = engine->sched_engine;
>   	struct i915_request **port = execlists->pending;
>   	struct i915_request ** const last_port = port + execlists->port_mask;
>   	struct i915_request *last, * const *active;
> @@ -1287,7 +1288,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   				     last->fence.context,
>   				     last->fence.seqno,
>   				     last->sched.attr.priority,
> -				     execlists->queue_priority_hint);
> +				     sched_engine->queue_priority_hint);
>   			record_preemption(execlists);
>   
>   			/*
> @@ -1313,7 +1314,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   				     yesno(timer_expired(&execlists->timer)),
>   				     last->fence.context, last->fence.seqno,
>   				     rq_prio(last),
> -				     execlists->queue_priority_hint,
> +				     sched_engine->queue_priority_hint,
>   				     yesno(timeslice_yield(execlists, last)));
>   
>   			/*
> @@ -1384,7 +1385,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   		GEM_BUG_ON(rq->engine != &ve->base);
>   		GEM_BUG_ON(rq->context != &ve->context);
>   
> -		if (unlikely(rq_prio(rq) < queue_prio(execlists))) {
> +		if (unlikely(rq_prio(rq) < queue_prio(sched_engine))) {
>   			spin_unlock(&ve->base.active.lock);
>   			break;
>   		}
> @@ -1405,7 +1406,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   			     yesno(engine != ve->siblings[0]));
>   
>   		WRITE_ONCE(ve->request, NULL);
> -		WRITE_ONCE(ve->base.execlists.queue_priority_hint, INT_MIN);
> +		WRITE_ONCE(ve->base.sched_engine->queue_priority_hint, INT_MIN);
>   
>   		rb = &ve->nodes[engine->id].rb;
>   		rb_erase_cached(rb, &execlists->virtual);
> @@ -1450,7 +1451,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   			break;
>   	}
>   
> -	while ((rb = rb_first_cached(&execlists->queue))) {
> +	while ((rb = rb_first_cached(&sched_engine->queue))) {
>   		struct i915_priolist *p = to_priolist(rb);
>   		struct i915_request *rq, *rn;
>   
> @@ -1529,7 +1530,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   			}
>   		}
>   
> -		rb_erase_cached(&p->node, &execlists->queue);
> +		rb_erase_cached(&p->node, &sched_engine->queue);
>   		i915_priolist_free(p);
>   	}
>   done:
> @@ -1551,7 +1552,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   	 * request triggering preemption on the next dequeue (or subsequent
>   	 * interrupt for secondary ports).
>   	 */
> -	execlists->queue_priority_hint = queue_prio(execlists);
> +	sched_engine->queue_priority_hint = queue_prio(sched_engine);
>   	spin_unlock(&engine->active.lock);
>   
>   	/*
> @@ -2123,8 +2124,8 @@ static void execlists_unhold(struct intel_engine_cs *engine,
>   	 */
>   	__execlists_unhold(rq);
>   
> -	if (rq_prio(rq) > engine->execlists.queue_priority_hint) {
> -		engine->execlists.queue_priority_hint = rq_prio(rq);
> +	if (rq_prio(rq) > engine->sched_engine->queue_priority_hint) {
> +		engine->sched_engine->queue_priority_hint = rq_prio(rq);
>   		tasklet_hi_schedule(&engine->execlists.tasklet);
>   	}
>   
> @@ -2455,12 +2456,12 @@ static void queue_request(struct intel_engine_cs *engine,
>   static bool submit_queue(struct intel_engine_cs *engine,
>   			 const struct i915_request *rq)
>   {
> -	struct intel_engine_execlists *execlists = &engine->execlists;
> +	struct i915_sched_engine *sched_engine = engine->sched_engine;
>   
> -	if (rq_prio(rq) <= execlists->queue_priority_hint)
> +	if (rq_prio(rq) <= sched_engine->queue_priority_hint)
>   		return false;
>   
> -	execlists->queue_priority_hint = rq_prio(rq);
> +	sched_engine->queue_priority_hint = rq_prio(rq);
>   	return true;
>   }
>   
> @@ -2486,7 +2487,7 @@ static void execlists_submit_request(struct i915_request *request)
>   	} else {
>   		queue_request(engine, request);
>   
> -		GEM_BUG_ON(RB_EMPTY_ROOT(&engine->execlists.queue.rb_root));
> +		GEM_BUG_ON(RB_EMPTY_ROOT(&engine->sched_engine->queue.rb_root));
>   		GEM_BUG_ON(list_empty(&request->sched.link));
>   
>   		if (submit_queue(engine, request))
> @@ -2969,12 +2970,13 @@ static void nop_submission_tasklet(struct tasklet_struct *t)
>   		from_tasklet(engine, t, execlists.tasklet);
>   
>   	/* The driver is wedged; don't process any more events. */
> -	WRITE_ONCE(engine->execlists.queue_priority_hint, INT_MIN);
> +	WRITE_ONCE(engine->sched_engine->queue_priority_hint, INT_MIN);
>   }
>   
>   static void execlists_reset_cancel(struct intel_engine_cs *engine)
>   {
>   	struct intel_engine_execlists * const execlists = &engine->execlists;
> +	struct i915_sched_engine * const sched_engine = engine->sched_engine;
>   	struct i915_request *rq, *rn;
>   	struct rb_node *rb;
>   	unsigned long flags;
> @@ -3006,7 +3008,7 @@ static void execlists_reset_cancel(struct intel_engine_cs *engine)
>   	intel_engine_signal_breadcrumbs(engine);
>   
>   	/* Flush the queued requests to the timeline list (for retiring). */
> -	while ((rb = rb_first_cached(&execlists->queue))) {
> +	while ((rb = rb_first_cached(&sched_engine->queue))) {
>   		struct i915_priolist *p = to_priolist(rb);
>   
>   		priolist_for_each_request_consume(rq, rn, p) {
> @@ -3016,7 +3018,7 @@ static void execlists_reset_cancel(struct intel_engine_cs *engine)
>   			}
>   		}
>   
> -		rb_erase_cached(&p->node, &execlists->queue);
> +		rb_erase_cached(&p->node, &sched_engine->queue);
>   		i915_priolist_free(p);
>   	}
>   
> @@ -3042,15 +3044,15 @@ static void execlists_reset_cancel(struct intel_engine_cs *engine)
>   			}
>   			i915_request_put(rq);
>   
> -			ve->base.execlists.queue_priority_hint = INT_MIN;
> +			ve->base.sched_engine->queue_priority_hint = INT_MIN;
>   		}
>   		spin_unlock(&ve->base.active.lock);
>   	}
>   
>   	/* Remaining _unready_ requests will be nop'ed when submitted */
>   
> -	execlists->queue_priority_hint = INT_MIN;
> -	execlists->queue = RB_ROOT_CACHED;
> +	sched_engine->queue_priority_hint = INT_MIN;
> +	sched_engine->queue = RB_ROOT_CACHED;
>   
>   	GEM_BUG_ON(__tasklet_is_enabled(&execlists->tasklet));
>   	execlists->tasklet.callback = nop_submission_tasklet;
> @@ -3286,7 +3288,7 @@ int intel_execlists_submission_setup(struct intel_engine_cs *engine)
>   
>   static struct list_head *virtual_queue(struct virtual_engine *ve)
>   {
> -	return &ve->base.execlists.default_priolist.requests;
> +	return &ve->base.sched_engine->default_priolist.requests;
>   }
>   
>   static void rcu_virtual_context_destroy(struct work_struct *wrk)
> @@ -3344,7 +3346,10 @@ static void rcu_virtual_context_destroy(struct work_struct *wrk)
>   	lrc_fini(&ve->context);
>   	intel_context_fini(&ve->context);
>   
> -	intel_breadcrumbs_free(ve->base.breadcrumbs);
> +	if (ve->base.breadcrumbs)
> +		intel_breadcrumbs_free(ve->base.breadcrumbs);
> +	if (ve->base.sched_engine)
> +		i915_sched_engine_put(ve->base.sched_engine);
>   	intel_engine_free_request_pool(&ve->base);
>   
>   	kfree(ve->bonds);
> @@ -3475,7 +3480,7 @@ static intel_engine_mask_t virtual_submission_mask(struct virtual_engine *ve)
>   
>   	ENGINE_TRACE(&ve->base, "rq=%llx:%lld, mask=%x, prio=%d\n",
>   		     rq->fence.context, rq->fence.seqno,
> -		     mask, ve->base.execlists.queue_priority_hint);
> +		     mask, ve->base.sched_engine->queue_priority_hint);
>   
>   	return mask;
>   }
> @@ -3484,7 +3489,7 @@ static void virtual_submission_tasklet(struct tasklet_struct *t)
>   {
>   	struct virtual_engine * const ve =
>   		from_tasklet(ve, t, base.execlists.tasklet);
> -	const int prio = READ_ONCE(ve->base.execlists.queue_priority_hint);
> +	const int prio = READ_ONCE(ve->base.sched_engine->queue_priority_hint);
>   	intel_engine_mask_t mask;
>   	unsigned int n;
>   
> @@ -3552,7 +3557,7 @@ static void virtual_submission_tasklet(struct tasklet_struct *t)
>   submit_engine:
>   		GEM_BUG_ON(RB_EMPTY_NODE(&node->rb));
>   		node->prio = prio;
> -		if (first && prio > sibling->execlists.queue_priority_hint)
> +		if (first && prio > sibling->sched_engine->queue_priority_hint)
>   			tasklet_hi_schedule(&sibling->execlists.tasklet);
>   
>   unlock_engine:
> @@ -3588,7 +3593,7 @@ static void virtual_submit_request(struct i915_request *rq)
>   		i915_request_put(ve->request);
>   	}
>   
> -	ve->base.execlists.queue_priority_hint = rq_prio(rq);
> +	ve->base.sched_engine->queue_priority_hint = rq_prio(rq);
>   	ve->request = i915_request_get(rq);
>   
>   	GEM_BUG_ON(!list_empty(virtual_queue(ve)));
> @@ -3684,6 +3689,12 @@ intel_execlists_create_virtual(struct intel_engine_cs **siblings,
>   	intel_engine_init_active(&ve->base, ENGINE_VIRTUAL);
>   	intel_engine_init_execlists(&ve->base);
>   
> +	ve->base.sched_engine = i915_sched_engine_create(ENGINE_VIRTUAL);
> +	if (!ve->base.sched_engine) {
> +		err = -ENOMEM;
> +		goto err_put;
> +	}
> +
>   	ve->base.cops = &virtual_context_ops;
>   	ve->base.request_alloc = execlists_request_alloc;
>   
> @@ -3692,7 +3703,6 @@ intel_execlists_create_virtual(struct intel_engine_cs **siblings,
>   	ve->base.bond_execute = virtual_bond_execute;
>   
>   	INIT_LIST_HEAD(virtual_queue(ve));
> -	ve->base.execlists.queue_priority_hint = INT_MIN;
>   	tasklet_setup(&ve->base.execlists.tasklet, virtual_submission_tasklet);
>   
>   	intel_context_init(&ve->context, &ve->base);
> @@ -3849,6 +3859,7 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine,
>   				   unsigned int max)
>   {
>   	const struct intel_engine_execlists *execlists = &engine->execlists;
> +	const struct i915_sched_engine *sched_engine = engine->sched_engine;
>   	struct i915_request *rq, *last;
>   	unsigned long flags;
>   	unsigned int count;
> @@ -3873,13 +3884,13 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine,
>   		show_request(m, last, "\t\t", 0);
>   	}
>   
> -	if (execlists->queue_priority_hint != INT_MIN)
> +	if (sched_engine->queue_priority_hint != INT_MIN)
>   		drm_printf(m, "\t\tQueue priority hint: %d\n",
> -			   READ_ONCE(execlists->queue_priority_hint));
> +			   READ_ONCE(sched_engine->queue_priority_hint));
>   
>   	last = NULL;
>   	count = 0;
> -	for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> +	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
>   		struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
>   
>   		priolist_for_each_request(rq, p) {
> diff --git a/drivers/gpu/drm/i915/gt/mock_engine.c b/drivers/gpu/drm/i915/gt/mock_engine.c
> index 32589c6625e1..b1fdba13e900 100644
> --- a/drivers/gpu/drm/i915/gt/mock_engine.c
> +++ b/drivers/gpu/drm/i915/gt/mock_engine.c
> @@ -283,6 +283,7 @@ static void mock_engine_release(struct intel_engine_cs *engine)
>   
>   	GEM_BUG_ON(timer_pending(&mock->hw_delay));
>   
> +	i915_sched_engine_put(engine->sched_engine);
>   	intel_breadcrumbs_free(engine->breadcrumbs);
>   
>   	intel_context_unpin(engine->kernel_context);
> @@ -345,6 +346,10 @@ int mock_engine_init(struct intel_engine_cs *engine)
>   {
>   	struct intel_context *ce;
>   
> +	engine->sched_engine = i915_sched_engine_create(ENGINE_MOCK);
> +	if (!engine->sched_engine)
> +		return -ENOMEM;
> +
>   	intel_engine_init_active(engine, ENGINE_MOCK);
>   	intel_engine_init_execlists(engine);
>   	intel_engine_init__pm(engine);
> @@ -352,7 +357,7 @@ int mock_engine_init(struct intel_engine_cs *engine)
>   
>   	engine->breadcrumbs = intel_breadcrumbs_create(NULL);
>   	if (!engine->breadcrumbs)
> -		return -ENOMEM;
> +		goto err_schedule;
>   
>   	ce = create_kernel_context(engine);
>   	if (IS_ERR(ce))
> @@ -366,6 +371,8 @@ int mock_engine_init(struct intel_engine_cs *engine)
>   
>   err_breadcrumbs:
>   	intel_breadcrumbs_free(engine->breadcrumbs);
> +err_schedule:
> +	i915_sched_engine_put(engine->sched_engine);
>   	return -ENOMEM;
>   }
>   
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 7c8ff9792f7b..5c5f33f40055 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -182,6 +182,7 @@ static void schedule_out(struct i915_request *rq)
>   static void __guc_dequeue(struct intel_engine_cs *engine)
>   {
>   	struct intel_engine_execlists * const execlists = &engine->execlists;
> +	struct i915_sched_engine * const sched_engine = engine->sched_engine;
>   	struct i915_request **first = execlists->inflight;
>   	struct i915_request ** const last_port = first + execlists->port_mask;
>   	struct i915_request *last = first[0];
> @@ -204,7 +205,7 @@ static void __guc_dequeue(struct intel_engine_cs *engine)
>   	 * event.
>   	 */
>   	port = first;
> -	while ((rb = rb_first_cached(&execlists->queue))) {
> +	while ((rb = rb_first_cached(&sched_engine->queue))) {
>   		struct i915_priolist *p = to_priolist(rb);
>   		struct i915_request *rq, *rn;
>   
> @@ -224,11 +225,11 @@ static void __guc_dequeue(struct intel_engine_cs *engine)
>   			last = rq;
>   		}
>   
> -		rb_erase_cached(&p->node, &execlists->queue);
> +		rb_erase_cached(&p->node, &sched_engine->queue);
>   		i915_priolist_free(p);
>   	}
>   done:
> -	execlists->queue_priority_hint =
> +	sched_engine->queue_priority_hint =
>   		rb ? to_priolist(rb)->priority : INT_MIN;
>   	if (submit) {
>   		*port = schedule_in(last, port - execlists->inflight);
> @@ -338,7 +339,7 @@ static void guc_reset_rewind(struct intel_engine_cs *engine, bool stalled)
>   
>   static void guc_reset_cancel(struct intel_engine_cs *engine)
>   {
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
> +	struct i915_sched_engine * const sched_engine = engine->sched_engine;
>   	struct i915_request *rq, *rn;
>   	struct rb_node *rb;
>   	unsigned long flags;
> @@ -368,7 +369,7 @@ static void guc_reset_cancel(struct intel_engine_cs *engine)
>   	}
>   
>   	/* Flush the queued requests to the timeline list (for retiring). */
> -	while ((rb = rb_first_cached(&execlists->queue))) {
> +	while ((rb = rb_first_cached(&sched_engine->queue))) {
>   		struct i915_priolist *p = to_priolist(rb);
>   
>   		priolist_for_each_request_consume(rq, rn, p) {
> @@ -378,14 +379,14 @@ static void guc_reset_cancel(struct intel_engine_cs *engine)
>   			i915_request_mark_complete(rq);
>   		}
>   
> -		rb_erase_cached(&p->node, &execlists->queue);
> +		rb_erase_cached(&p->node, &sched_engine->queue);
>   		i915_priolist_free(p);
>   	}
>   
>   	/* Remaining _unready_ requests will be nop'ed when submitted */
>   
> -	execlists->queue_priority_hint = INT_MIN;
> -	execlists->queue = RB_ROOT_CACHED;
> +	sched_engine->queue_priority_hint = INT_MIN;
> +	sched_engine->queue = RB_ROOT_CACHED;
>   
>   	spin_unlock_irqrestore(&engine->active.lock, flags);
>   }
> @@ -514,7 +515,7 @@ static void guc_submit_request(struct i915_request *rq)
>   
>   	queue_request(engine, rq, rq_prio(rq));
>   
> -	GEM_BUG_ON(RB_EMPTY_ROOT(&engine->execlists.queue.rb_root));
> +	GEM_BUG_ON(RB_EMPTY_ROOT(&engine->sched_engine->queue.rb_root));
>   	GEM_BUG_ON(list_empty(&rq->sched.link));
>   
>   	tasklet_hi_schedule(&engine->execlists.tasklet);
> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
> index efa638c3acc7..4953874a9ba6 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler.c
> +++ b/drivers/gpu/drm/i915/i915_scheduler.c
> @@ -40,7 +40,7 @@ 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)
> +static void assert_priolists(struct i915_sched_engine * const sched_engine)
>   {
>   	struct rb_node *rb;
>   	long last_prio;
> @@ -48,11 +48,11 @@ static void assert_priolists(struct intel_engine_execlists * const execlists)
>   	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
>   		return;
>   
> -	GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
> -		   rb_first(&execlists->queue.rb_root));
> +	GEM_BUG_ON(rb_first_cached(&sched_engine->queue) !=
> +		   rb_first(&sched_engine->queue.rb_root));
>   
>   	last_prio = INT_MAX;
> -	for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> +	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
>   		const struct i915_priolist *p = to_priolist(rb);
>   
>   		GEM_BUG_ON(p->priority > last_prio);
> @@ -63,21 +63,21 @@ static void assert_priolists(struct intel_engine_execlists * const execlists)
>   struct list_head *
>   i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
>   {
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
> +	struct i915_sched_engine * const sched_engine = engine->sched_engine;
>   	struct i915_priolist *p;
>   	struct rb_node **parent, *rb;
>   	bool first = true;
>   
>   	lockdep_assert_held(&engine->active.lock);
> -	assert_priolists(execlists);
> +	assert_priolists(sched_engine);
>   
> -	if (unlikely(execlists->no_priolist))
> +	if (unlikely(sched_engine->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;
> +	parent = &sched_engine->queue.rb_root.rb_node;
>   	while (*parent) {
>   		rb = *parent;
>   		p = to_priolist(rb);
> @@ -92,7 +92,7 @@ i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
>   	}
>   
>   	if (prio == I915_PRIORITY_NORMAL) {
> -		p = &execlists->default_priolist;
> +		p = &sched_engine->default_priolist;
>   	} else {
>   		p = kmem_cache_alloc(global.slab_priorities, GFP_ATOMIC);
>   		/* Convert an allocation failure to a priority bump */
> @@ -107,7 +107,7 @@ i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
>   			 * requests, so if userspace lied about their
>   			 * dependencies that reordering may be visible.
>   			 */
> -			execlists->no_priolist = true;
> +			sched_engine->no_priolist = true;
>   			goto find_priolist;
>   		}
>   	}
> @@ -116,7 +116,7 @@ i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
>   	INIT_LIST_HEAD(&p->requests);
>   
>   	rb_link_node(&p->node, rb, parent);
> -	rb_insert_color_cached(&p->node, &execlists->queue, first);
> +	rb_insert_color_cached(&p->node, &sched_engine->queue, first);
>   
>   	return &p->requests;
>   }
> @@ -184,7 +184,7 @@ static void kick_submission(struct intel_engine_cs *engine,
>   	 * 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)
> +	if (prio <= engine->sched_engine->queue_priority_hint)
>   		return;
>   
>   	rcu_read_lock();
> @@ -208,7 +208,7 @@ static void kick_submission(struct intel_engine_cs *engine,
>   		     inflight->fence.context, inflight->fence.seqno,
>   		     inflight->sched.attr.priority);
>   
> -	engine->execlists.queue_priority_hint = prio;
> +	engine->sched_engine->queue_priority_hint = prio;
>   	if (need_preempt(prio, rq_prio(inflight)))
>   		tasklet_hi_schedule(&engine->execlists.tasklet);
>   
> @@ -489,6 +489,31 @@ void i915_request_show_with_schedule(struct drm_printer *m,
>   	rcu_read_unlock();
>   }
>   
> +void i915_sched_engine_free(struct kref *kref)
> +{
> +	struct i915_sched_engine *sched_engine =
> +		container_of(kref, typeof(*sched_engine), ref);
> +
> +	kfree(sched_engine);
> +}
> +
> +struct i915_sched_engine *
> +i915_sched_engine_create(unsigned int subclass)

subclass is unused here. My preference would be to move adding this 
param to the patch that actually makes use of it (i.e. patch 4), but if 
you want to keep it here because it makes the series split easier at 
least add a mention in the commit message of what's this for and why it 
is here and not in the patch that uses it.

Apart from these minor comments, the mechanical replacement looks fine. 
I'd prefer if we tried to avoid accessing sched_engine internals from 
the backends now, but that can come as a follow up (and I see some of it 
is already in patch 2).

With the comment addressed:

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>

Daniele

> +{
> +	struct i915_sched_engine *sched_engine;
> +
> +	sched_engine = kzalloc(sizeof(*sched_engine), GFP_KERNEL);
> +	if (!sched_engine)
> +		return NULL;
> +
> +	kref_init(&sched_engine->ref);
> +
> +	sched_engine->queue = RB_ROOT_CACHED;
> +	sched_engine->queue_priority_hint = INT_MIN;
> +
> +	return sched_engine;
> +}
> +
>   static void i915_global_scheduler_shrink(void)
>   {
>   	kmem_cache_shrink(global.slab_dependencies);
> diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h
> index 858a0938f47a..91a04e34cac5 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler.h
> +++ b/drivers/gpu/drm/i915/i915_scheduler.h
> @@ -48,6 +48,24 @@ static inline void i915_priolist_free(struct i915_priolist *p)
>   		__i915_priolist_free(p);
>   }
>   
> +struct i915_sched_engine *
> +i915_sched_engine_create(unsigned int subclass);
> +
> +void i915_sched_engine_free(struct kref *kref);
> +
> +static inline struct i915_sched_engine *
> +i915_sched_engine_get(struct i915_sched_engine *sched_engine)
> +{
> +	kref_get(&sched_engine->ref);
> +	return sched_engine;
> +}
> +
> +static inline void
> +i915_sched_engine_put(struct i915_sched_engine *sched_engine)
> +{
> +	kref_put(&sched_engine->ref, i915_sched_engine_free);
> +}
> +
>   void i915_request_show_with_schedule(struct drm_printer *m,
>   				     const struct i915_request *rq,
>   				     const char *prefix,
> diff --git a/drivers/gpu/drm/i915/i915_scheduler_types.h b/drivers/gpu/drm/i915/i915_scheduler_types.h
> index 343ed44d5ed4..4a7c9f06b40b 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler_types.h
> +++ b/drivers/gpu/drm/i915/i915_scheduler_types.h
> @@ -91,4 +91,51 @@ struct i915_dependency {
>   				&(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;
> +
> +	/**
> +	 * @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;
> +};
> +
>   #endif /* _I915_SCHEDULER_TYPES_H_ */