Re: [Intel-gfx] [PATCH 06/20] drm/i915: add I915_BO_ALLOC_TOPDOWN

Thomas Hellström
2022-01-31T15:28:27Z

On 1/26/22 16:21, Matthew Auld wrote:
> If the user doesn't require CPU access for the buffer, then
> ALLOC_TOPDOWN should be used, in order to prioritise allocating in the
> non-mappable portion of LMEM.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>

I was wondering how this would work best with user-space not supplying
any hints. Thinking that mappable LMEM buffers would be a minority,
wouldn't it be better to have TOPDOWN behaviour set by default. It would
then be migrated to mappable only if needed. And if the first usage is a
cpu-map it would either be mapped in system or immediately migrated from
pageless to mappable LMEM?

> ---
> drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 15 +++++++++++----
> drivers/gpu/drm/i915/gem/i915_gem_pages.c | 3 +++
> drivers/gpu/drm/i915/gem/i915_gem_region.c | 5 +++++
> drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 13 ++++++++++---
> drivers/gpu/drm/i915/gt/intel_gt.c | 4 +++-
> drivers/gpu/drm/i915/i915_vma.c | 3 +++
> drivers/gpu/drm/i915/intel_region_ttm.c | 11 ++++++++---
> drivers/gpu/drm/i915/selftests/mock_region.c | 7 +------
> 8 files changed, 44 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> index 71e778ecaeb8..29285aaf0477 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> @@ -319,15 +319,22 @@ struct drm_i915_gem_object {
> #define I915_BO_ALLOC_PM_VOLATILE BIT(4)
> /* Object needs to be restored early using memcpy during resume */
> #define I915_BO_ALLOC_PM_EARLY BIT(5)
> +/*
> + * Object is likely never accessed by the CPU. This will prioritise the BO to be
> + * allocated in the non-mappable portion of lmem. This is merely a hint, and if
> + * dealing with userspace objects the CPU fault handler is free to ignore this.
> + */
> +#define I915_BO_ALLOC_TOPDOWN BIT(6)
> #define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
> I915_BO_ALLOC_VOLATILE | \
> I915_BO_ALLOC_CPU_CLEAR | \
> I915_BO_ALLOC_USER | \
> I915_BO_ALLOC_PM_VOLATILE | \
> - I915_BO_ALLOC_PM_EARLY)
> -#define I915_BO_READONLY BIT(6)
> -#define I915_TILING_QUIRK_BIT 7 /* unknown swizzling; do not release! */
> -#define I915_BO_PROTECTED BIT(8)
> + I915_BO_ALLOC_PM_EARLY | \
> + I915_BO_ALLOC_TOPDOWN)
> +#define I915_BO_READONLY BIT(7)
> +#define I915_TILING_QUIRK_BIT 8 /* unknown swizzling; do not release! */
> +#define I915_BO_PROTECTED BIT(9)
> /**
> * @mem_flags - Mutable placement-related flags
> *
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index 7d2211fbe548..a95b4d72619f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -346,6 +346,9 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
> !i915_gem_object_has_iomem(obj))
> return ERR_PTR(-ENXIO);
>
> + if (WARN_ON_ONCE(obj->flags & I915_BO_ALLOC_TOPDOWN))
> + return ERR_PTR(-EINVAL);
> +
> assert_object_held(obj);
>
> pinned = !(type & I915_MAP_OVERRIDE);
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_region.c b/drivers/gpu/drm/i915/gem/i915_gem_region.c
> index a4350227e9ae..f91e5a9c759d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_region.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_region.c
> @@ -45,6 +45,11 @@ i915_gem_object_create_region(struct intel_memory_region *mem,
>
> GEM_BUG_ON(flags & ~I915_BO_ALLOC_FLAGS);
>
> + if (WARN_ON_ONCE(flags & I915_BO_ALLOC_TOPDOWN &&
> + (flags & I915_BO_ALLOC_CPU_CLEAR ||
> + flags & I915_BO_ALLOC_PM_EARLY)))
> + return ERR_PTR(-EINVAL);
> +
> if (!mem)
> return ERR_PTR(-ENODEV);
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index d9a04c7d41b1..e60b677ecd54 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -127,10 +127,14 @@ i915_ttm_place_from_region(const struct intel_memory_region *mr,
> place->mem_type = intel_region_to_ttm_type(mr);
>
> if (flags & I915_BO_ALLOC_CONTIGUOUS)
> - place->flags = TTM_PL_FLAG_CONTIGUOUS;
> + place->flags |= TTM_PL_FLAG_CONTIGUOUS;
> if (mr->io_size && mr->io_size < mr->total) {
> - place->fpfn = 0;
> - place->lpfn = mr->io_size >> PAGE_SHIFT;
> + if (flags & I915_BO_ALLOC_TOPDOWN) {
> + place->flags |= TTM_PL_FLAG_TOPDOWN;
> + } else {
> + place->fpfn = 0;
> + place->lpfn = mr->io_size >> PAGE_SHIFT;
> + }
> }
> }
>
> @@ -890,6 +894,9 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
> if (!obj)
> return VM_FAULT_SIGBUS;
>
> + if (obj->flags & I915_BO_ALLOC_TOPDOWN)
> + return -EINVAL;
> +
> /* Sanity check that we allow writing into this object */
> if (unlikely(i915_gem_object_is_readonly(obj) &&
> area->vm_flags & VM_WRITE))
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
> index 622cdfed8a8b..8b83a771a2f7 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
> @@ -454,7 +454,9 @@ static int intel_gt_init_scratch(struct intel_gt *gt, unsigned int size)
> struct i915_vma *vma;
> int ret;
>
> - obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE);
> + obj = i915_gem_object_create_lmem(i915, size,
> + I915_BO_ALLOC_VOLATILE |
> + I915_BO_ALLOC_TOPDOWN);
> if (IS_ERR(obj))
> obj = i915_gem_object_create_stolen(i915, size);
> if (IS_ERR(obj))
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index b1816a835abf..b2fdaa74e4b6 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -528,6 +528,9 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
> void __iomem *ptr;
> int err;
>
> + if (WARN_ON_ONCE(vma->obj->flags & I915_BO_ALLOC_TOPDOWN))
> + return IO_ERR_PTR(-EINVAL);
> +
> if (!i915_gem_object_is_lmem(vma->obj)) {
> if (GEM_WARN_ON(!i915_vma_is_map_and_fenceable(vma))) {
> err = -ENODEV;
> diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
> index 4689192d5e8d..282802aed174 100644
> --- a/drivers/gpu/drm/i915/intel_region_ttm.c
> +++ b/drivers/gpu/drm/i915/intel_region_ttm.c
> @@ -199,13 +199,18 @@ intel_region_ttm_resource_alloc(struct intel_memory_region *mem,
> struct ttm_resource *res;
> int ret;
>
> + if (flags & I915_BO_ALLOC_CONTIGUOUS)
> + place.flags |= TTM_PL_FLAG_CONTIGUOUS;
> if (mem->io_size && mem->io_size < mem->total) {
> - place.fpfn = 0;
> - place.lpfn = mem->io_size >> PAGE_SHIFT;
> + if (flags & I915_BO_ALLOC_TOPDOWN) {
> + place.flags |= TTM_PL_FLAG_TOPDOWN;
> + } else {
> + place.fpfn = 0;
> + place.lpfn = mem->io_size >> PAGE_SHIFT;
> + }
> }
>
> mock_bo.base.size = size;
> - place.flags = flags;
>
> ret = man->func->alloc(man, &mock_bo, &place, &res);
> if (ret == -ENOSPC)
> diff --git a/drivers/gpu/drm/i915/selftests/mock_region.c b/drivers/gpu/drm/i915/selftests/mock_region.c
> index 467eeae6d5f0..f64325491f35 100644
> --- a/drivers/gpu/drm/i915/selftests/mock_region.c
> +++ b/drivers/gpu/drm/i915/selftests/mock_region.c
> @@ -22,17 +22,12 @@ static void mock_region_put_pages(struct drm_i915_gem_object *obj,
>
> static int mock_region_get_pages(struct drm_i915_gem_object *obj)
> {
> - unsigned int flags;
> struct sg_table *pages;
> int err;
>
> - flags = 0;
> - if (obj->flags & I915_BO_ALLOC_CONTIGUOUS)
> - flags |= TTM_PL_FLAG_CONTIGUOUS;
> -
> obj->mm.res = intel_region_ttm_resource_alloc(obj->mm.region,
> obj->base.size,
> - flags);
> + obj->flags);
> if (IS_ERR(obj->mm.res))
> return PTR_ERR(obj->mm.res);
>