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

Daniel Vetter
2019-10-08T09:25:58Z

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