Re: [PATCH v2 4/7] drm/i915/gtt/dgfx: place the PD in LMEM

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 27/04/2021 09:54, Matthew Auld wrote:
> It's a requirement that for dgfx we place all the paging structures in
> device local-memory.
>
> v2: use i915_coherent_map_type()
> v3: improve the shared dma-resv object comment
>
> Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/gen8_ppgtt.c |  5 ++++-
>   drivers/gpu/drm/i915/gt/intel_gtt.c  | 30 +++++++++++++++++++++++++---
>   drivers/gpu/drm/i915/gt/intel_gtt.h  |  1 +
>   3 files changed, 32 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> index f83496836f0f..11fb5df45a0f 100644
> --- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c
> @@ -712,7 +712,10 @@ struct i915_ppgtt *gen8_ppgtt_create(struct intel_gt *gt)
>   	 */
>   	ppgtt->vm.has_read_only = !IS_GEN_RANGE(gt->i915, 11, 12);
>   
> -	ppgtt->vm.alloc_pt_dma = alloc_pt_dma;
> +	if (HAS_LMEM(gt->i915))
> +		ppgtt->vm.alloc_pt_dma = alloc_pt_lmem;
> +	else
> +		ppgtt->vm.alloc_pt_dma = alloc_pt_dma;
>   
>   	err = gen8_init_scratch(&ppgtt->vm);
>   	if (err)
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
> index d386b89e2758..061c39d2ad51 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
> @@ -7,10 +7,26 @@
>   
>   #include <linux/fault-inject.h>
>   
> +#include "gem/i915_gem_lmem.h"
>   #include "i915_trace.h"
>   #include "intel_gt.h"
>   #include "intel_gtt.h"
>   
> +struct drm_i915_gem_object *alloc_pt_lmem(struct i915_address_space *vm, int sz)
> +{
> +	struct drm_i915_gem_object *obj;
> +
> +	obj = i915_gem_object_create_lmem(vm->i915, sz, 0);
> +	/*
> +	 * Ensure all paging structures for this vm share the same dma-resv
> +	 * object underneath, with the idea that one object_lock() will lock
> +	 * them all at once.

Okay but I am still missing the part about why is this beneficial and 
not a downside. I suppose it is not a concept added by this patch so not 
fair to ask for explanation here anyway.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko

> +	 */
> +	if (!IS_ERR(obj))
> +		obj->base.resv = &vm->resv;
> +	return obj;
> +}
> +
>   struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz)
>   {
>   	struct drm_i915_gem_object *obj;
> @@ -19,7 +35,11 @@ struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz)
>   		i915_gem_shrink_all(vm->i915);
>   
>   	obj = i915_gem_object_create_internal(vm->i915, sz);
> -	/* ensure all dma objects have the same reservation class */
> +	/*
> +	 * Ensure all paging structures for this vm share the same dma-resv
> +	 * object underneath, with the idea that one object_lock() will lock
> +	 * them all at once.
> +	 */
>   	if (!IS_ERR(obj))
>   		obj->base.resv = &vm->resv;
>   	return obj;
> @@ -27,9 +47,11 @@ struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz)
>   
>   int map_pt_dma(struct i915_address_space *vm, struct drm_i915_gem_object *obj)
>   {
> +	enum i915_map_type type;
>   	void *vaddr;
>   
> -	vaddr = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB);
> +	type = i915_coherent_map_type(vm->i915, obj, true);
> +	vaddr = i915_gem_object_pin_map_unlocked(obj, type);
>   	if (IS_ERR(vaddr))
>   		return PTR_ERR(vaddr);
>   
> @@ -39,9 +61,11 @@ int map_pt_dma(struct i915_address_space *vm, struct drm_i915_gem_object *obj)
>   
>   int map_pt_dma_locked(struct i915_address_space *vm, struct drm_i915_gem_object *obj)
>   {
> +	enum i915_map_type type;
>   	void *vaddr;
>   
> -	vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB);
> +	type = i915_coherent_map_type(vm->i915, obj, true);
> +	vaddr = i915_gem_object_pin_map(obj, type);
>   	if (IS_ERR(vaddr))
>   		return PTR_ERR(vaddr);
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
> index 40e486704558..44ce27c51631 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
> @@ -527,6 +527,7 @@ int setup_scratch_page(struct i915_address_space *vm);
>   void free_scratch(struct i915_address_space *vm);
>   
>   struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz);
> +struct drm_i915_gem_object *alloc_pt_lmem(struct i915_address_space *vm, int sz);
>   struct i915_page_table *alloc_pt(struct i915_address_space *vm);
>   struct i915_page_directory *alloc_pd(struct i915_address_space *vm);
>   struct i915_page_directory *__alloc_pd(int npde);
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