Re: [PATCH 09/12] HACK drm/i915/scheduler: emulate a scheduler for guc

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

On 02/11/2016 17:50, Chris Wilson wrote:
> This emulates execlists on top of the GuC in order to defer submission of
> requests to the hardware. This deferral allows time for high priority
> requests to gazump their way to the head of the queue, however it nerfs
> the GuC by converting it back into a simple execlist (where the CPU has
> to wake up after every request to feed new commands into the GuC).

How big is the performance hit? :)

Regards,

Tvrtko

> ---
>  drivers/gpu/drm/i915/i915_guc_submission.c | 83 ++++++++++++++++++++++++++----
>  drivers/gpu/drm/i915/i915_irq.c            |  4 +-
>  drivers/gpu/drm/i915/intel_lrc.c           |  3 --
>  3 files changed, 75 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index bab0c2fc3bce..601b8777d3fd 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -469,7 +469,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
>  	u32 freespace;
>  	int ret;
>
> -	spin_lock(&gc->wq_lock);
> +	spin_lock_irq(&gc->wq_lock);
>  	freespace = CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size);
>  	freespace -= gc->wq_rsvd;
>  	if (likely(freespace >= wqi_size)) {
> @@ -479,7 +479,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
>  		gc->no_wq_space++;
>  		ret = -EAGAIN;
>  	}
> -	spin_unlock(&gc->wq_lock);
> +	spin_unlock_irq(&gc->wq_lock);
>
>  	return ret;
>  }
> @@ -491,9 +491,9 @@ void i915_guc_wq_unreserve(struct drm_i915_gem_request *request)
>
>  	GEM_BUG_ON(READ_ONCE(gc->wq_rsvd) < wqi_size);
>
> -	spin_lock(&gc->wq_lock);
> +	spin_lock_irq(&gc->wq_lock);
>  	gc->wq_rsvd -= wqi_size;
> -	spin_unlock(&gc->wq_lock);
> +	spin_unlock_irq(&gc->wq_lock);
>  }
>
>  /* Construct a Work Item and append it to the GuC's Work Queue */
> @@ -658,6 +658,70 @@ static void i915_guc_submit(struct drm_i915_gem_request *rq)
>  	spin_unlock(&client->wq_lock);
>  }
>
> +static bool i915_guc_dequeue(struct intel_engine_cs *engine)
> +{
> +	struct execlist_port *port = engine->execlist_port;
> +	struct drm_i915_gem_request *last = port[0].request;
> +	unsigned long flags;
> +	struct rb_node *rb;
> +	bool submit = false;
> +
> +	spin_lock_irqsave(&engine->timeline->lock, flags);
> +	rb = engine->execlist_first;
> +	while (rb) {
> +		struct drm_i915_gem_request *cursor =
> +			rb_entry(rb, typeof(*cursor), priotree.node);
> +
> +		if (last && cursor->ctx != last->ctx) {
> +			if (port != engine->execlist_port)
> +				break;
> +
> +			i915_gem_request_assign(&port->request, last);
> +			dma_fence_enable_sw_signaling(&last->fence);
> +			port++;
> +		}
> +
> +		rb = rb_next(rb);
> +		rb_erase(&cursor->priotree.node, &engine->execlist_queue);
> +		RB_CLEAR_NODE(&cursor->priotree.node);
> +		cursor->priotree.priority = INT_MAX;
> +
> +		i915_guc_submit(cursor);
> +		last = cursor;
> +		submit = true;
> +	}
> +	if (submit) {
> +		i915_gem_request_assign(&port->request, last);
> +		dma_fence_enable_sw_signaling(&last->fence);
> +		engine->execlist_first = rb;
> +	}
> +	spin_unlock_irqrestore(&engine->timeline->lock, flags);
> +
> +	return submit;
> +}
> +
> +static void i915_guc_irq_handler(unsigned long data)
> +{
> +	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
> +	struct execlist_port *port = engine->execlist_port;
> +	struct drm_i915_gem_request *rq;
> +	bool submit;
> +
> +	do {
> +		rq = port[0].request;
> +		while (rq && i915_gem_request_completed(rq)) {
> +			i915_gem_request_put(rq);
> +			rq = port[1].request;
> +			port[0].request = rq;
> +			port[1].request = NULL;
> +		}
> +
> +		submit = false;
> +		if (!port[1].request)
> +			submit = i915_guc_dequeue(engine);
> +	} while (submit);
> +}
> +
>  /*
>   * Everything below here is concerned with setup & teardown, and is
>   * therefore not part of the somewhat time-critical batch-submission
> @@ -1524,16 +1588,13 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
>
>  	/* Take over from manual control of ELSP (execlists) */
>  	for_each_engine(engine, dev_priv, id) {
> -		engine->submit_request = i915_guc_submit;
> -		engine->schedule = NULL;
> +		tasklet_init(&engine->irq_tasklet,
> +			     i915_guc_irq_handler,
> +			     (unsigned long)engine);
>
>  		/* Replay the current set of previously submitted requests */
> -		list_for_each_entry(request,
> -				    &engine->timeline->requests, link) {
> +		list_for_each_entry(request, &engine->timeline->requests, link)
>  			client->wq_rsvd += sizeof(struct guc_wq_item);
> -			if (i915_sw_fence_done(&request->submit))
> -				i915_guc_submit(request);
> -		}
>  	}
>
>  	return 0;
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 6d7505b5c5e7..217f63e17e4e 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1341,8 +1341,10 @@ static void snb_gt_irq_handler(struct drm_i915_private *dev_priv,
>  static __always_inline void
>  gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
>  {
> -	if (iir & (GT_RENDER_USER_INTERRUPT << test_shift))
> +	if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) {
> +		tasklet_schedule(&engine->irq_tasklet);
>  		notify_ring(engine);
> +	}
>  	if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift))
>  		tasklet_schedule(&engine->irq_tasklet);
>  }
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 70ac74c959bd..d17c0fff9642 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1350,9 +1350,6 @@ static void reset_common_ring(struct intel_engine_cs *engine,
>  	request->ring->last_retired_head = -1;
>  	intel_ring_update_space(request->ring);
>
> -	if (i915.enable_guc_submission)
> -		return;
> -
>  	/* Catch up with any missed context-switch interrupts */
>  	I915_WRITE(RING_CONTEXT_STATUS_PTR(engine), _MASKED_FIELD(0xffff, 0));
>  	if (request->ctx != port[0].request->ctx) {
>
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