[Intel-gfx] [PATCH v4] drm/i915/guc: Move GuC wq_check_space to alloc_request_extras

[Dave Gordon]

On 16/12/15 19:45, yu.dai at intel.com wrote:
> From: Alex Dai <yu.dai at intel.com>
>
> Split GuC work queue space checking from submission and move it to
> ring_alloc_request_extras. The reason is that failure in later
> i915_add_request() won't be handled. In the case timeout happens,
> driver can return early in order to handle the error.
>
> v1: Move wq_reserve_space to ring_reserve_space
> v2: Move wq_reserve_space to alloc_request_extras (Chris Wilson)
> v3: The work queue head pointer is cached by driver now. So we can
>      quickly return if space is available.
>      s/reserve/check/g (Dave Gordon)
> v4: Update cached wq head after ring doorbell; check wq space before
>      ring doorbell in case unexpected error happens; call wq space
>      check only when GuC submission is enabled. (Dave Gordon)
>
> Signed-off-by: Alex Dai <yu.dai at intel.com>

LGTM.
Reviewed-by: Dave Gordon <david.s.gordon at intel.com>

> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index ef20071..7554d16 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -247,6 +247,9 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
>   			db_exc.cookie = 1;
>   	}
>
> +	/* Finally, update the cached copy of the GuC's WQ head */
> +	gc->wq_head = desc->head;
> +
>   	kunmap_atomic(base);
>   	return ret;
>   }
> @@ -472,28 +475,30 @@ static void guc_fini_ctx_desc(struct intel_guc *guc,
>   			     sizeof(desc) * client->ctx_index);
>   }
>
> -/* Get valid workqueue item and return it back to offset */
> -static int guc_get_workqueue_space(struct i915_guc_client *gc, u32 *offset)
> +int i915_guc_wq_check_space(struct i915_guc_client *gc)
>   {
>   	struct guc_process_desc *desc;
>   	void *base;
>   	u32 size = sizeof(struct guc_wq_item);
>   	int ret = -ETIMEDOUT, timeout_counter = 200;
>
> +	if (!gc)
> +		return 0;
> +
> +	/* Quickly return if wq space is available since last time we cache the
> +	 * head position. */
> +	if (CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size) >= size)
> +		return 0;
> +
>   	base = kmap_atomic(i915_gem_object_get_page(gc->client_obj, 0));
>   	desc = base + gc->proc_desc_offset;
>
>   	while (timeout_counter-- > 0) {
> -		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
> -			*offset = gc->wq_tail;
> +		gc->wq_head = desc->head;
>
> -			/* advance the tail for next workqueue item */
> -			gc->wq_tail += size;
> -			gc->wq_tail &= gc->wq_size - 1;
> -
> -			/* this will break the loop */
> -			timeout_counter = 0;
> +		if (CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size) >= size) {
>   			ret = 0;
> +			break;
>   		}
>
>   		if (timeout_counter)
> @@ -511,12 +516,16 @@ static int guc_add_workqueue_item(struct i915_guc_client *gc,
>   	enum intel_ring_id ring_id = rq->ring->id;
>   	struct guc_wq_item *wqi;
>   	void *base;
> -	u32 tail, wq_len, wq_off = 0;
> -	int ret;
> +	u32 tail, wq_len, wq_off, space;
> +
> +	space = CIRC_SPACE(gc->wq_tail, gc->wq_head, gc->wq_size);
> +	if (WARN_ON(space < sizeof(struct guc_wq_item)))
> +		return -ENOSPC; /* shouldn't happen */
>
> -	ret = guc_get_workqueue_space(gc, &wq_off);
> -	if (ret)
> -		return ret;
> +	/* postincrement WQ tail for next time */
> +	wq_off = gc->wq_tail;
> +	gc->wq_tail += sizeof(struct guc_wq_item);
> +	gc->wq_tail &= gc->wq_size - 1;
>
>   	/* For now workqueue item is 4 DWs; workqueue buffer is 2 pages. So we
>   	 * should not have the case where structure wqi is across page, neither
> diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
> index 0e048bf..5cf555d 100644
> --- a/drivers/gpu/drm/i915/intel_guc.h
> +++ b/drivers/gpu/drm/i915/intel_guc.h
> @@ -43,6 +43,7 @@ struct i915_guc_client {
>   	uint32_t wq_offset;
>   	uint32_t wq_size;
>   	uint32_t wq_tail;
> +	uint32_t wq_head;
>
>   	/* GuC submission statistics & status */
>   	uint64_t submissions[I915_NUM_RINGS];
> @@ -123,5 +124,6 @@ int i915_guc_submit(struct i915_guc_client *client,
>   		    struct drm_i915_gem_request *rq);
>   void i915_guc_submission_disable(struct drm_device *dev);
>   void i915_guc_submission_fini(struct drm_device *dev);
> +int i915_guc_wq_check_space(struct i915_guc_client *client);
>
>   #endif
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 272f36f..cd232d2 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -667,6 +667,19 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
>   			return ret;
>   	}
>
> +	if (i915.enable_guc_submission) {
> +		/*
> +		 * Check that the GuC has space for the request before
> +		 * going any further, as the i915_add_request() call
> +		 * later on mustn't fail ...
> +		 */
> +		struct intel_guc *guc = &request->i915->guc;
> +
> +		ret = i915_guc_wq_check_space(guc->execbuf_client);
> +		if (ret)
> +			return ret;
> +	}
> +
>   	return 0;
>   }
>
>