[Intel-gfx] [PATCH v5 07/35] drm/i915: Prepare retire_requests to handle out-of-order seqnos

[Jesse Barnes]

On 02/18/2016 06:26 AM, John.C.Harrison at Intel.com wrote:
> From: John Harrison <John.C.Harrison at Intel.com>
> 
> A major point of the GPU scheduler is that it re-orders batch buffers
> after they have been submitted to the driver. This leads to requests
> completing out of order. In turn, this means that the retire
> processing can no longer assume that all completed entries are at the
> front of the list. Rather than attempting to re-order the request list
> on a regular basis, it is better to simply scan the entire list.
> 
> v2: Removed deferred free code as no longer necessary due to request
> handling updates.
> 
> For: VIZ-1587
> Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 31 +++++++++++++------------------
>  1 file changed, 13 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 7d9aa24..0003cfc 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3233,6 +3233,7 @@ void i915_gem_reset(struct drm_device *dev)
>  void
>  i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
>  {
> +	struct drm_i915_gem_object *obj, *obj_next;
>  	struct drm_i915_gem_request *req, *req_next;
>  	LIST_HEAD(list_head);
>  
> @@ -3245,37 +3246,31 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
>  	 */
>  	i915_gem_request_notify(ring, false);
>  
> +	/*
> +	 * Note that request entries might be out of order due to rescheduling
> +	 * and pre-emption. Thus both lists must be processed in their entirety
> +	 * rather than stopping at the first non-complete entry.
> +	 */
> +
>  	/* Retire requests first as we use it above for the early return.
>  	 * If we retire requests last, we may use a later seqno and so clear
>  	 * the requests lists without clearing the active list, leading to
>  	 * confusion.
>  	 */
> -	while (!list_empty(&ring->request_list)) {
> -		struct drm_i915_gem_request *request;
> -
> -		request = list_first_entry(&ring->request_list,
> -					   struct drm_i915_gem_request,
> -					   list);
> -
> -		if (!i915_gem_request_completed(request))
> -			break;
> +	list_for_each_entry_safe(req, req_next, &ring->request_list, list) {
> +		if (!i915_gem_request_completed(req))
> +			continue;
>  
> -		i915_gem_request_retire(request);
> +		i915_gem_request_retire(req);
>  	}
>  
>  	/* Move any buffers on the active list that are no longer referenced
>  	 * by the ringbuffer to the flushing/inactive lists as appropriate,
>  	 * before we free the context associated with the requests.
>  	 */
> -	while (!list_empty(&ring->active_list)) {
> -		struct drm_i915_gem_object *obj;
> -
> -		obj = list_first_entry(&ring->active_list,
> -				      struct drm_i915_gem_object,
> -				      ring_list[ring->id]);
> -
> +	list_for_each_entry_safe(obj, obj_next, &ring->active_list, ring_list[ring->id]) {
>  		if (!list_empty(&obj->last_read_req[ring->id]->list))
> -			break;
> +			continue;
>  
>  		i915_gem_object_retire__read(obj, ring->id);
>  	}
> 

Reviewed-by: Jesse Barnes <jbarnes at virtuousgeek.org>