Re: [PATCH 1/4] drm/ttm: add multihop infrastrucutre (v2)

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On Mon, Nov 09, 2020 at 10:54:29AM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied@xxxxxxxxxx>
> 
> Currently drivers get called to move a buffer, but if they have to
> move it temporarily through another space (SYSTEM->VRAM via TT)
> then they can end up with a lot of ttm->driver->ttm call stacks,
> if the temprorary space moves requires eviction.
> 
> Instead of letting the driver do all the placement/space for the
> temporary, allow it to report back (-EMULTIHOP) and a placement (hop)
> to the move code, which will then do the temporary move, and the
> correct placement move afterwards.
> 
> This removes a lot of code from drivers, at the expense of
> adding some midlayering. I've some further ideas on how to turn
> it inside out, but I think this is a good solution to the call
> stack problems.
> 
> v2: separate out the driver patches, add WARN for getting
> MULTHOP in paths we shouldn't (Daniel)
> 
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    |  3 +-
>  drivers/gpu/drm/drm_gem_vram_helper.c      |  3 +-
>  drivers/gpu/drm/nouveau/nouveau_bo.c       |  3 +-
>  drivers/gpu/drm/qxl/qxl_ttm.c              |  3 +-
>  drivers/gpu/drm/radeon/radeon_ttm.c        |  3 +-
>  drivers/gpu/drm/ttm/ttm_bo.c               | 68 +++++++++++++++++++---
>  drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c |  3 +-
>  include/drm/ttm/ttm_bo_driver.h            |  7 ++-
>  8 files changed, 77 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index c01c060e4ac5..ce0d82802333 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -656,7 +656,8 @@ static bool amdgpu_mem_visible(struct amdgpu_device *adev,
>   */
>  static int amdgpu_bo_move(struct ttm_buffer_object *bo, bool evict,
>  			  struct ttm_operation_ctx *ctx,
> -			  struct ttm_resource *new_mem)
> +			  struct ttm_resource *new_mem,
> +			  struct ttm_place *hop)
>  {
>  	struct amdgpu_device *adev;
>  	struct amdgpu_bo *abo;
> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> index 16d68c04ea5d..2cec7b1482b8 100644
> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> @@ -964,7 +964,8 @@ static void bo_driver_delete_mem_notify(struct ttm_buffer_object *bo)
>  static int bo_driver_move(struct ttm_buffer_object *bo,
>  			  bool evict,
>  			  struct ttm_operation_ctx *ctx,
> -			  struct ttm_resource *new_mem)
> +			  struct ttm_resource *new_mem,
> +			  struct ttm_place *hop)
>  {
>  	struct drm_gem_vram_object *gbo;
>  
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 8133377d865d..fee07b9d19ed 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -1023,7 +1023,8 @@ nouveau_bo_vm_cleanup(struct ttm_buffer_object *bo,
>  static int
>  nouveau_bo_move(struct ttm_buffer_object *bo, bool evict,
>  		struct ttm_operation_ctx *ctx,
> -		struct ttm_resource *new_reg)
> +		struct ttm_resource *new_reg,
> +		struct ttm_place *hop)
>  {
>  	struct nouveau_drm *drm = nouveau_bdev(bo->bdev);
>  	struct nouveau_bo *nvbo = nouveau_bo(bo);
> diff --git a/drivers/gpu/drm/qxl/qxl_ttm.c b/drivers/gpu/drm/qxl/qxl_ttm.c
> index a80d59634143..128c38c8a837 100644
> --- a/drivers/gpu/drm/qxl/qxl_ttm.c
> +++ b/drivers/gpu/drm/qxl/qxl_ttm.c
> @@ -140,7 +140,8 @@ static void qxl_bo_move_notify(struct ttm_buffer_object *bo,
>  
>  static int qxl_bo_move(struct ttm_buffer_object *bo, bool evict,
>  		       struct ttm_operation_ctx *ctx,
> -		       struct ttm_resource *new_mem)
> +		       struct ttm_resource *new_mem,
> +		       struct ttm_place *hop)
>  {
>  	struct ttm_resource *old_mem = &bo->mem;
>  	int ret;
> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index 95038ac3382e..29062dbea299 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -303,7 +303,8 @@ static int radeon_move_ram_vram(struct ttm_buffer_object *bo,
>  
>  static int radeon_bo_move(struct ttm_buffer_object *bo, bool evict,
>  			  struct ttm_operation_ctx *ctx,
> -			  struct ttm_resource *new_mem)
> +			  struct ttm_resource *new_mem,
> +			  struct ttm_place *hop)
>  {
>  	struct radeon_device *rdev;
>  	struct radeon_bo *rbo;
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index e2a124b3affb..9f840f2a7836 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -231,7 +231,8 @@ EXPORT_SYMBOL(ttm_bo_bulk_move_lru_tail);
>  
>  static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>  				  struct ttm_resource *mem, bool evict,
> -				  struct ttm_operation_ctx *ctx)
> +				  struct ttm_operation_ctx *ctx,
> +				  struct ttm_place *hop)
>  {
>  	struct ttm_bo_device *bdev = bo->bdev;
>  	struct ttm_resource_manager *old_man = ttm_manager_type(bdev, bo->mem.mem_type);
> @@ -259,9 +260,12 @@ static int ttm_bo_handle_move_mem(struct ttm_buffer_object *bo,
>  		}
>  	}
>  
> -	ret = bdev->driver->move(bo, evict, ctx, mem);
> -	if (ret)
> +	ret = bdev->driver->move(bo, evict, ctx, mem, hop);
> +	if (ret) {
> +		if (ret == -EMULTIHOP)
> +			return ret;
>  		goto out_err;
> +	}
>  
>  	ctx->bytes_moved += bo->num_pages << PAGE_SHIFT;
>  	return 0;
> @@ -566,6 +570,7 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
>  	struct ttm_bo_device *bdev = bo->bdev;
>  	struct ttm_resource evict_mem;
>  	struct ttm_placement placement;
> +	struct ttm_place hop = {};
>  	int ret = 0;
>  
>  	dma_resv_assert_held(bo->base.resv);
> @@ -596,8 +601,9 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
>  		goto out;
>  	}
>  
> -	ret = ttm_bo_handle_move_mem(bo, &evict_mem, true, ctx);
> +	ret = ttm_bo_handle_move_mem(bo, &evict_mem, true, ctx, &hop);
>  	if (unlikely(ret)) {
> +		WARN(ret == -EMULTIHOP, "Unexpected multihop in eviction - likely driver bug\n");
>  		if (ret != -ERESTARTSYS)
>  			pr_err("Buffer eviction failed\n");
>  		ttm_resource_free(bo, &evict_mem);
> @@ -936,11 +942,39 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
>  }
>  EXPORT_SYMBOL(ttm_bo_mem_space);
>  
> +static int ttm_bo_bounce_temp_buffer(struct ttm_buffer_object *bo,
> +				     struct ttm_resource *mem,
> +				     struct ttm_operation_ctx *ctx,
> +				     struct ttm_place *hop)
> +{
> +	struct ttm_placement hop_placement;
> +	int ret;
> +	struct ttm_resource hop_mem = *mem;
> +
> +	hop_mem.mm_node = NULL;
> +	hop_mem.mem_type = TTM_PL_SYSTEM;
> +	hop_mem.placement = 0;
> +
> +	hop_placement.num_placement = hop_placement.num_busy_placement = 1;
> +	hop_placement.placement = hop_placement.busy_placement = hop;
> +
> +	/* find space in the bounce domain */
> +	ret = ttm_bo_mem_space(bo, &hop_placement, &hop_mem, ctx);
> +	if (ret)
> +		return ret;
> +	/* move to the bounce domain */
> +	ret = ttm_bo_handle_move_mem(bo, &hop_mem, false, ctx, NULL);
> +	if (ret)
> +		return ret;
> +	return 0;
> +}
> +
>  static int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
>  			      struct ttm_placement *placement,
>  			      struct ttm_operation_ctx *ctx)
>  {
>  	int ret = 0;
> +	struct ttm_place hop = {};
>  	struct ttm_resource mem;
>  
>  	dma_resv_assert_held(bo->base.resv);
> @@ -954,12 +988,25 @@ static int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
>  
>  	/*
>  	 * Determine where to move the buffer.
> +	 *
> +	 * If driver determines move is going to need
> +	 * an extra step then it will return -EMULTIHOP
> +	 * and the buffer will be moved to the temporary
> +	 * stop and the driver will be called to make
> +	 * the second hop.
>  	 */
> +bounce:
>  	ret = ttm_bo_mem_space(bo, placement, &mem, ctx);
>  	if (ret)
> -		goto out_unlock;
> -	ret = ttm_bo_handle_move_mem(bo, &mem, false, ctx);
> -out_unlock:
> +		return ret;
> +	ret = ttm_bo_handle_move_mem(bo, &mem, false, ctx, &hop);
> +	if (ret == -EMULTIHOP) {
> +		ret = ttm_bo_bounce_temp_buffer(bo, &mem, ctx, &hop);
> +		if (ret)
> +			return ret;
> +		/* try and move to final place now. */
> +		goto bounce;
> +	}
>  	if (ret)
>  		ttm_resource_free(bo, &mem);
>  	return ret;
> @@ -1432,15 +1479,18 @@ int ttm_bo_swapout(struct ttm_operation_ctx *ctx)
>  	if (bo->mem.mem_type != TTM_PL_SYSTEM) {
>  		struct ttm_operation_ctx ctx = { false, false };
>  		struct ttm_resource evict_mem;
> +		struct ttm_place hop = {};
>  
>  		evict_mem = bo->mem;
>  		evict_mem.mm_node = NULL;
>  		evict_mem.placement = 0;
>  		evict_mem.mem_type = TTM_PL_SYSTEM;
>  
> -		ret = ttm_bo_handle_move_mem(bo, &evict_mem, true, &ctx);
> -		if (unlikely(ret != 0))
> +		ret = ttm_bo_handle_move_mem(bo, &evict_mem, true, &ctx, &hop);
> +		if (unlikely(ret != 0)) {
> +			WARN(ret == -EMULTIHOP, "Unexpected multihop in swaput - likely driver bug.\n");
>  			goto out;
> +		}
>  	}
>  
>  	/**
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
> index 51f70bea41cc..6a04261ce760 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c
> @@ -695,7 +695,8 @@ static void vmw_swap_notify(struct ttm_buffer_object *bo)
>  static int vmw_move(struct ttm_buffer_object *bo,
>  		    bool evict,
>  		    struct ttm_operation_ctx *ctx,
> -		    struct ttm_resource *new_mem)
> +		    struct ttm_resource *new_mem,
> +		    struct ttm_place *hop)
>  {
>  	struct ttm_resource_manager *old_man = ttm_manager_type(bo->bdev, bo->mem.mem_type);
>  	struct ttm_resource_manager *new_man = ttm_manager_type(bo->bdev, new_mem->mem_type);
> diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
> index da8208f43378..f02f7cf9ae90 100644
> --- a/include/drm/ttm/ttm_bo_driver.h
> +++ b/include/drm/ttm/ttm_bo_driver.h
> @@ -121,6 +121,8 @@ struct ttm_bo_driver {
>  	 * Return the bo flags for a buffer which is not mapped to the hardware.
>  	 * These will be placed in proposed_flags so that when the move is
>  	 * finished, they'll end up in bo->mem.flags
> +	 * This should not cause multihop evictions, and the core will warn
> +	 * if one is proposed.
>  	 */
>  
>  	void (*evict_flags)(struct ttm_buffer_object *bo,
> @@ -134,12 +136,15 @@ struct ttm_bo_driver {
>  	 * the graphics address space
>  	 * @ctx: context for this move with parameters
>  	 * @new_mem: the new memory region receiving the buffer
> +	 @ @hop: placement for driver directed intermediate hop
>  	 *
>  	 * Move a buffer between two memory regions.
> +	 * Returns errno -EMULTIHOP if driver requests a hop
>  	 */
>  	int (*move)(struct ttm_buffer_object *bo, bool evict,
>  		    struct ttm_operation_ctx *ctx,
> -		    struct ttm_resource *new_mem);
> +		    struct ttm_resource *new_mem,
> +		    struct ttm_place *hop);

I think the warnings look all good, and everything else too.

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

On the = {} bikeshed I frankly don't care, since for anything where this
matters vs memset you really should have a pad-less structure (by padding
the structure properly). So imo = {} is perfectly fine.
-Daniel

>  
>  	/**
>  	 * struct ttm_bo_driver_member verify_access
> -- 
> 2.27.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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