Re: [Intel-gfx] [RFC PATCH 44/97] drm/i915/guc: Implement GuC submission tasklet

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 06/05/2021 20:13, Matthew Brost wrote:
> Implement GuC submission tasklet for new interface. The new GuC
> interface uses H2G to submit contexts to the GuC. Since H2G use a single
> channel, a single tasklet submits is used for the submission path. As
> such a global struct intel_engine_cs has been added to leverage the
> existing scheduling code.
> 
> Also the per engine interrupt handler has been updated to disable the
> rescheduling of the physical engine tasklet, when using GuC scheduling,
> as the physical engine tasklet is no longer used.
> 
> In this patch the field, guc_id, has been added to intel_context and is
> not assigned. Patches later in the series will assign this value.
> 
> Cc: John Harrison <john.c.harrison@intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_context_types.h |   9 +
>   drivers/gpu/drm/i915/gt/uc/intel_guc.h        |   4 +
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 233 +++++++++---------
>   3 files changed, 127 insertions(+), 119 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index ed8c447a7346..bb6fef7eae52 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -136,6 +136,15 @@ struct intel_context {
>   	struct intel_sseu sseu;
>   
>   	u8 wa_bb_page; /* if set, page num reserved for context workarounds */
> +
> +	/* GuC scheduling state that does not require a lock. */
> +	atomic_t guc_sched_state_no_lock;
> +
> +	/*
> +	 * GuC lrc descriptor ID - Not assigned in this patch but future patches
> +	 * in the series will.
> +	 */
> +	u16 guc_id;
>   };
>   
>   #endif /* __INTEL_CONTEXT_TYPES__ */
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> index 2eb6c497e43c..d32866fe90ad 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> @@ -30,6 +30,10 @@ struct intel_guc {
>   	struct intel_guc_log log;
>   	struct intel_guc_ct ct;
>   
> +	/* Global engine used to submit requests to GuC */
> +	struct i915_sched_engine *sched_engine;
> +	struct i915_request *stalled_request;
> +
>   	/* intel_guc_recv interrupt related state */
>   	spinlock_t irq_lock;
>   	unsigned int msg_enabled_mask;
> 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 c2b6d27404b7..0955a8b00ee8 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -60,6 +60,30 @@
>   
>   #define GUC_REQUEST_SIZE 64 /* bytes */
>   
> +/*
> + * Below is a set of functions which control the GuC scheduling state which do
> + * not require a lock as all state transitions are mutually exclusive. i.e. It
> + * is not possible for the context pinning code and submission, for the same
> + * context, to be executing simultaneously.
> + */

Is the statement that some other locks, or other guarantees, serialise 
modification of this state, and if so, why is it using atomics?

Regards,

Tvrtko

> +#define SCHED_STATE_NO_LOCK_ENABLED			BIT(0)
> +static inline bool context_enabled(struct intel_context *ce)
> +{
> +	return (atomic_read(&ce->guc_sched_state_no_lock) &
> +		SCHED_STATE_NO_LOCK_ENABLED);
> +}
> +
> +static inline void set_context_enabled(struct intel_context *ce)
> +{
> +	atomic_or(SCHED_STATE_NO_LOCK_ENABLED, &ce->guc_sched_state_no_lock);
> +}
> +
> +static inline void clr_context_enabled(struct intel_context *ce)
> +{
> +	atomic_and((u32)~SCHED_STATE_NO_LOCK_ENABLED,
> +		   &ce->guc_sched_state_no_lock);
> +}
> +
>   static inline struct i915_priolist *to_priolist(struct rb_node *rb)
>   {
>   	return rb_entry(rb, struct i915_priolist, node);
> @@ -122,37 +146,29 @@ static inline void set_lrc_desc_registered(struct intel_guc *guc, u32 id,
>   	xa_store_irq(&guc->context_lookup, id, ce, GFP_ATOMIC);
>   }
>   
> -static void guc_add_request(struct intel_guc *guc, struct i915_request *rq)
> +static int guc_add_request(struct intel_guc *guc, struct i915_request *rq)
>   {
> -	/* Leaving stub as this function will be used in future patches */
> -}
> +	int err;
> +	struct intel_context *ce = rq->context;
> +	u32 action[3];
> +	int len = 0;
> +	bool enabled = context_enabled(ce);
>   
> -/*
> - * When we're doing submissions using regular execlists backend, writing to
> - * ELSP from CPU side is enough to make sure that writes to ringbuffer pages
> - * pinned in mappable aperture portion of GGTT are visible to command streamer.
> - * Writes done by GuC on our behalf are not guaranteeing such ordering,
> - * therefore, to ensure the flush, we're issuing a POSTING READ.
> - */
> -static void flush_ggtt_writes(struct i915_vma *vma)
> -{
> -	if (i915_vma_is_map_and_fenceable(vma))
> -		intel_uncore_posting_read_fw(vma->vm->gt->uncore,
> -					     GUC_STATUS);
> -}
> +	if (!enabled) {
> +		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT_MODE_SET;
> +		action[len++] = ce->guc_id;
> +		action[len++] = GUC_CONTEXT_ENABLE;
> +	} else {
> +		action[len++] = INTEL_GUC_ACTION_SCHED_CONTEXT;
> +		action[len++] = ce->guc_id;
> +	}
>   
> -static void guc_submit(struct intel_engine_cs *engine,
> -		       struct i915_request **out,
> -		       struct i915_request **end)
> -{
> -	struct intel_guc *guc = &engine->gt->uc.guc;
> +	err = intel_guc_send_nb(guc, action, len);
>   
> -	do {
> -		struct i915_request *rq = *out++;
> +	if (!enabled && !err)
> +		set_context_enabled(ce);
>   
> -		flush_ggtt_writes(rq->ring->vma);
> -		guc_add_request(guc, rq);
> -	} while (out != end);
> +	return err;
>   }
>   
>   static inline int rq_prio(const struct i915_request *rq)
> @@ -160,125 +176,88 @@ static inline int rq_prio(const struct i915_request *rq)
>   	return rq->sched.attr.priority;
>   }
>   
> -static struct i915_request *schedule_in(struct i915_request *rq, int idx)
> -{
> -	trace_i915_request_in(rq, idx);
> -
> -	/*
> -	 * Currently we are not tracking the rq->context being inflight
> -	 * (ce->inflight = rq->engine). It is only used by the execlists
> -	 * backend at the moment, a similar counting strategy would be
> -	 * required if we generalise the inflight tracking.
> -	 */
> -
> -	__intel_gt_pm_get(rq->engine->gt);
> -	return i915_request_get(rq);
> -}
> -
> -static void schedule_out(struct i915_request *rq)
> -{
> -	trace_i915_request_out(rq);
> -
> -	intel_gt_pm_put_async(rq->engine->gt);
> -	i915_request_put(rq);
> -}
> -
> -static void __guc_dequeue(struct intel_engine_cs *engine)
> +static int guc_dequeue_one_context(struct intel_guc *guc)
>   {
> -	struct i915_sched_engine * const sched_engine = engine->sched_engine;
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
> -	struct i915_request **first = execlists->inflight;
> -	struct i915_request ** const last_port = first + execlists->port_mask;
> -	struct i915_request *last = first[0];
> -	struct i915_request **port;
> +	struct i915_sched_engine * const sched_engine = guc->sched_engine;
> +	struct i915_request *last = NULL;
>   	bool submit = false;
>   	struct rb_node *rb;
> +	int ret;
>   
> -	lockdep_assert_held(&engine->sched_engine->lock);
> -
> -	if (last) {
> -		if (*++first)
> -			return;
> +	lockdep_assert_held(&sched_engine->lock);
>   
> -		last = NULL;
> +	if (guc->stalled_request) {
> +		submit = true;
> +		last = guc->stalled_request;
> +		goto resubmit;
>   	}
>   
> -	/*
> -	 * We write directly into the execlists->inflight queue and don't use
> -	 * the execlists->pending queue, as we don't have a distinct switch
> -	 * event.
> -	 */
> -	port = first;
>   	while ((rb = rb_first_cached(&sched_engine->queue))) {
>   		struct i915_priolist *p = to_priolist(rb);
>   		struct i915_request *rq, *rn;
>   
>   		priolist_for_each_request_consume(rq, rn, p) {
> -			if (last && rq->context != last->context) {
> -				if (port == last_port)
> -					goto done;
> -
> -				*port = schedule_in(last,
> -						    port - execlists->inflight);
> -				port++;
> -			}
> +			if (last && rq->context != last->context)
> +				goto done;
>   
>   			list_del_init(&rq->sched.link);
> +
>   			__i915_request_submit(rq);
> -			submit = true;
> +
> +			trace_i915_request_in(rq, 0);
>   			last = rq;
> +			submit = true;
>   		}
>   
>   		rb_erase_cached(&p->node, &sched_engine->queue);
>   		i915_priolist_free(p);
>   	}
>   done:
> -	sched_engine->queue_priority_hint =
> -		rb ? to_priolist(rb)->priority : INT_MIN;
>   	if (submit) {
> -		*port = schedule_in(last, port - execlists->inflight);
> -		*++port = NULL;
> -		guc_submit(engine, first, port);
> +		last->context->lrc_reg_state[CTX_RING_TAIL] =
> +			intel_ring_set_tail(last->ring, last->tail);
> +resubmit:
> +		/*
> +		 * We only check for -EBUSY here even though it is possible for
> +		 * -EDEADLK to be returned. If -EDEADLK is returned, the GuC has
> +		 * died and a full GPU needs to be done. The hangcheck will
> +		 * eventually detect that the GuC has died and trigger this
> +		 * reset so no need to handle -EDEADLK here.
> +		 */
> +		ret = guc_add_request(guc, last);
> +		if (ret == -EBUSY) {
> +			i915_sched_engine_kick(sched_engine);
> +			guc->stalled_request = last;
> +			return false;
> +		}
>   	}
> -	execlists->active = execlists->inflight;
> +
> +	guc->stalled_request = NULL;
> +	return submit;
>   }
>   
>   static void guc_submission_tasklet(struct tasklet_struct *t)
>   {
>   	struct i915_sched_engine *sched_engine =
>   		from_tasklet(sched_engine, t, tasklet);
> -	struct intel_engine_cs * const engine = sched_engine->engine;
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
> -	struct i915_request **port, *rq;
>   	unsigned long flags;
> +	bool loop;
>   
> -	spin_lock_irqsave(&engine->sched_engine->lock, flags);
> -
> -	for (port = execlists->inflight; (rq = *port); port++) {
> -		if (!i915_request_completed(rq))
> -			break;
> +	spin_lock_irqsave(&sched_engine->lock, flags);
>   
> -		schedule_out(rq);
> -	}
> -	if (port != execlists->inflight) {
> -		int idx = port - execlists->inflight;
> -		int rem = ARRAY_SIZE(execlists->inflight) - idx;
> -		memmove(execlists->inflight, port, rem * sizeof(*port));
> -	}
> -
> -	__guc_dequeue(engine);
> +	do {
> +		loop = guc_dequeue_one_context(&sched_engine->engine->gt->uc.guc);
> +	} while (loop);
>   
> -	i915_sched_engine_reset_on_empty(engine->sched_engine);
> +	i915_sched_engine_reset_on_empty(sched_engine);
>   
> -	spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
> +	spin_unlock_irqrestore(&sched_engine->lock, flags);
>   }
>   
>   static void cs_irq_handler(struct intel_engine_cs *engine, u16 iir)
>   {
> -	if (iir & GT_RENDER_USER_INTERRUPT) {
> +	if (iir & GT_RENDER_USER_INTERRUPT)
>   		intel_engine_signal_breadcrumbs(engine);
> -		i915_sched_engine_hi_kick(engine->sched_engine);
> -	}
>   }
>   
>   static void guc_reset_prepare(struct intel_engine_cs *engine)
> @@ -351,6 +330,10 @@ static void guc_reset_cancel(struct intel_engine_cs *engine)
>   	struct rb_node *rb;
>   	unsigned long flags;
>   
> +	/* Can be called during boot if GuC fails to load */
> +	if (!engine->gt)
> +		return;
> +
>   	ENGINE_TRACE(engine, "\n");
>   
>   	/*
> @@ -437,8 +420,11 @@ int intel_guc_submission_init(struct intel_guc *guc)
>   
>   void intel_guc_submission_fini(struct intel_guc *guc)
>   {
> -	if (guc->lrc_desc_pool)
> -		guc_lrc_desc_pool_destroy(guc);
> +	if (!guc->lrc_desc_pool)
> +		return;
> +
> +	guc_lrc_desc_pool_destroy(guc);
> +	i915_sched_engine_put(guc->sched_engine);
>   }
>   
>   static int guc_context_alloc(struct intel_context *ce)
> @@ -503,32 +489,32 @@ static int guc_request_alloc(struct i915_request *request)
>   	return 0;
>   }
>   
> -static inline void queue_request(struct intel_engine_cs *engine,
> +static inline void queue_request(struct i915_sched_engine *sched_engine,
>   				 struct i915_request *rq,
>   				 int prio)
>   {
>   	GEM_BUG_ON(!list_empty(&rq->sched.link));
>   	list_add_tail(&rq->sched.link,
> -		      i915_sched_lookup_priolist(engine->sched_engine, prio));
> +		      i915_sched_lookup_priolist(sched_engine, prio));
>   	set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
>   }
>   
>   static void guc_submit_request(struct i915_request *rq)
>   {
> -	struct intel_engine_cs *engine = rq->engine;
> +	struct i915_sched_engine *sched_engine = rq->engine->sched_engine;
>   	unsigned long flags;
>   
>   	/* Will be called from irq-context when using foreign fences. */
> -	spin_lock_irqsave(&engine->sched_engine->lock, flags);
> +	spin_lock_irqsave(&sched_engine->lock, flags);
>   
> -	queue_request(engine, rq, rq_prio(rq));
> +	queue_request(sched_engine, rq, rq_prio(rq));
>   
> -	GEM_BUG_ON(i915_sched_engine_is_empty(engine->sched_engine));
> +	GEM_BUG_ON(i915_sched_engine_is_empty(sched_engine));
>   	GEM_BUG_ON(list_empty(&rq->sched.link));
>   
> -	i915_sched_engine_hi_kick(engine->sched_engine);
> +	i915_sched_engine_hi_kick(sched_engine);
>   
> -	spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
> +	spin_unlock_irqrestore(&sched_engine->lock, flags);
>   }
>   
>   static void sanitize_hwsp(struct intel_engine_cs *engine)
> @@ -606,8 +592,6 @@ static void guc_release(struct intel_engine_cs *engine)
>   {
>   	engine->sanitize = NULL; /* no longer in control, nothing to sanitize */
>   
> -	tasklet_kill(&engine->sched_engine->tasklet);
> -
>   	intel_engine_cleanup_common(engine);
>   	lrc_fini_wa_ctx(engine);
>   }
> @@ -678,6 +662,7 @@ static inline void guc_default_irqs(struct intel_engine_cs *engine)
>   int intel_guc_submission_setup(struct intel_engine_cs *engine)
>   {
>   	struct drm_i915_private *i915 = engine->i915;
> +	struct intel_guc *guc = &engine->gt->uc.guc;
>   
>   	/*
>   	 * The setup relies on several assumptions (e.g. irqs always enabled)
> @@ -685,8 +670,18 @@ int intel_guc_submission_setup(struct intel_engine_cs *engine)
>   	 */
>   	GEM_BUG_ON(INTEL_GEN(i915) < 11);
>   
> -	tasklet_setup(&engine->sched_engine->tasklet, guc_submission_tasklet);
> -	engine->sched_engine->schedule = i915_schedule;
> +	if (!guc->sched_engine) {
> +		guc->sched_engine = i915_sched_engine_create(ENGINE_VIRTUAL);
> +		if (!guc->sched_engine)
> +			return -ENOMEM;
> +
> +		guc->sched_engine->schedule = i915_schedule;
> +		guc->sched_engine->engine = engine;
> +		tasklet_setup(&guc->sched_engine->tasklet,
> +			      guc_submission_tasklet);
> +	}
> +	i915_sched_engine_put(engine->sched_engine);
> +	engine->sched_engine = i915_sched_engine_get(guc->sched_engine);
>   
>   	guc_default_vfuncs(engine);
>   	guc_default_irqs(engine);
>