Re: [PATCH 2/4] drm/ttm: use the parent resv for ghost objects v2

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 29, 2019 at 04:29:15PM +0200, Christian König wrote:
> This way we can even pipeline imported BO evictions.
> 
> v2: Limit this to only cases when the parent object uses a separate
>     reservation object as well. This fixes another OOM problem.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

Since I read quite a bit of ttm I figured I'll review this too, but I'm
totally lost. And git blame gives me at best commits with one-liner commit
messages, and the docs aren't explaining much at all either (and generally
they didn't get updated at all with all the changes in the past years). 

I have a vague idea of what you're doing here, but not enough to do review
with any confidence. And from other ttm patches from amd it feels a lot
like we have essentially a bus factor of 1 for all things ttm :-/
-Daniel

> ---
>  drivers/gpu/drm/ttm/ttm_bo_util.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index fe81c565e7ef..2ebe9fe7f6c8 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -517,7 +517,9 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>  	kref_init(&fbo->base.kref);
>  	fbo->base.destroy = &ttm_transfered_destroy;
>  	fbo->base.acc_size = 0;
> -	fbo->base.base.resv = &fbo->base.base._resv;
> +	if (bo->base.resv == &bo->base._resv)
> +		fbo->base.base.resv = &fbo->base.base._resv;
> +
>  	dma_resv_init(fbo->base.base.resv);
>  	ret = dma_resv_trylock(fbo->base.base.resv);
>  	WARN_ON(!ret);
> @@ -716,7 +718,7 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
>  		if (ret)
>  			return ret;
>  
> -		dma_resv_add_excl_fence(ghost_obj->base.resv, fence);
> +		dma_resv_add_excl_fence(&ghost_obj->base._resv, fence);
>  
>  		/**
>  		 * If we're not moving to fixed memory, the TTM object
> @@ -729,7 +731,7 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
>  		else
>  			bo->ttm = NULL;
>  
> -		ttm_bo_unreserve(ghost_obj);
> +		dma_resv_unlock(&ghost_obj->base._resv);
>  		ttm_bo_put(ghost_obj);
>  	}
>  
> @@ -772,7 +774,7 @@ int ttm_bo_pipeline_move(struct ttm_buffer_object *bo,
>  		if (ret)
>  			return ret;
>  
> -		dma_resv_add_excl_fence(ghost_obj->base.resv, fence);
> +		dma_resv_add_excl_fence(&ghost_obj->base._resv, fence);
>  
>  		/**
>  		 * If we're not moving to fixed memory, the TTM object
> @@ -785,7 +787,7 @@ int ttm_bo_pipeline_move(struct ttm_buffer_object *bo,
>  		else
>  			bo->ttm = NULL;
>  
> -		ttm_bo_unreserve(ghost_obj);
> +		dma_resv_unlock(&ghost_obj->base._resv);
>  		ttm_bo_put(ghost_obj);
>  
>  	} else if (from->flags & TTM_MEMTYPE_FLAG_FIXED) {
> @@ -841,7 +843,7 @@ int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
>  	if (ret)
>  		return ret;
>  
> -	ret = dma_resv_copy_fences(ghost->base.resv, bo->base.resv);
> +	ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
>  	/* Last resort, wait for the BO to be idle when we are OOM */
>  	if (ret)
>  		ttm_bo_wait(bo, false, false);
> @@ -850,7 +852,7 @@ int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
>  	bo->mem.mem_type = TTM_PL_SYSTEM;
>  	bo->ttm = NULL;
>  
> -	ttm_bo_unreserve(ghost);
> +	dma_resv_unlock(&ghost->base._resv);
>  	ttm_bo_put(ghost);
>  
>  	return 0;
> -- 
> 2.17.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch