[Intel-gfx] [PATCH 17/28] drm/i915: use the new iterator in i915_gem_busy_ioctl v2

[Tvrtko Ursulin]

On 01/10/2021 11:05, Christian König wrote:
> This makes the function much simpler since the complex
> retry logic is now handled else where.
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Sorry I retract until you add the text about the increased cost of the 
added atomics. I think the point is important to discuss given proposal 
goes from zero atomics to num_fences * 2 (fence get/put unless I am 
mistaken) atomics per busy ioctl. That makes me lean towards just 
leaving this as is since it is not that complex.

Regards,

Tvrtko

> ---
>   drivers/gpu/drm/i915/gem/i915_gem_busy.c | 35 ++++++++++--------------
>   1 file changed, 14 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_busy.c b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> index 6234e17259c1..dc72b36dae54 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
> @@ -82,8 +82,8 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
>   {
>   	struct drm_i915_gem_busy *args = data;
>   	struct drm_i915_gem_object *obj;
> -	struct dma_resv_list *list;
> -	unsigned int seq;
> +	struct dma_resv_iter cursor;
> +	struct dma_fence *fence;
>   	int err;
>   
>   	err = -ENOENT;
> @@ -109,27 +109,20 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
>   	 * to report the overall busyness. This is what the wait-ioctl does.
>   	 *
>   	 */
> -retry:
> -	seq = raw_read_seqcount(&obj->base.resv->seq);
> -
> -	/* Translate the exclusive fence to the READ *and* WRITE engine */
> -	args->busy = busy_check_writer(dma_resv_excl_fence(obj->base.resv));
> -
> -	/* Translate shared fences to READ set of engines */
> -	list = dma_resv_shared_list(obj->base.resv);
> -	if (list) {
> -		unsigned int shared_count = list->shared_count, i;
> -
> -		for (i = 0; i < shared_count; ++i) {
> -			struct dma_fence *fence =
> -				rcu_dereference(list->shared[i]);
> -
> +	args->busy = 0;
> +	dma_resv_iter_begin(&cursor, obj->base.resv, true);
> +	dma_resv_for_each_fence_unlocked(&cursor, fence) {
> +		if (dma_resv_iter_is_restarted(&cursor))
> +			args->busy = 0;
> +
> +		if (dma_resv_iter_is_exclusive(&cursor))
> +			/* Translate the exclusive fence to the READ *and* WRITE engine */
> +			args->busy |= busy_check_writer(fence);
> +		else
> +			/* Translate shared fences to READ set of engines */
>   			args->busy |= busy_check_reader(fence);
> -		}
>   	}
> -
> -	if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
> -		goto retry;
> +	dma_resv_iter_end(&cursor);
>   
>   	err = 0;
>   out:
>