Re: [PATCH v11 5/5] drm/amdgpu: add drm buddy support to amdgpu

[Arunpravin <arunpravin.paneerselvam@amd.com>]

On 04/02/22 6:53 pm, Christian König wrote:
> Am 04.02.22 um 12:22 schrieb Arunpravin:
>> On 28/01/22 7:48 pm, Matthew Auld wrote:
>>> On Thu, 27 Jan 2022 at 14:11, Arunpravin
>>> <Arunpravin.PaneerSelvam@amd.com> wrote:
>>>> - Remove drm_mm references and replace with drm buddy functionalities
>>>> - Add res cursor support for drm buddy
>>>>
>>>> v2(Matthew Auld):
>>>>    - replace spinlock with mutex as we call kmem_cache_zalloc
>>>>      (..., GFP_KERNEL) in drm_buddy_alloc() function
>>>>
>>>>    - lock drm_buddy_block_trim() function as it calls
>>>>      mark_free/mark_split are all globally visible
>>>>
>>>> v3(Matthew Auld):
>>>>    - remove trim method error handling as we address the failure case
>>>>      at drm_buddy_block_trim() function
>>>>
>>>> v4:
>>>>    - fix warnings reported by kernel test robot <lkp@intel.com>
>>>>
>>>> v5:
>>>>    - fix merge conflict issue
>>>>
>>>> v6:
>>>>    - fix warnings reported by kernel test robot <lkp@intel.com>
>>>>
>>>> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
>>>> ---
>>>>   drivers/gpu/drm/Kconfig                       |   1 +
>>>>   .../gpu/drm/amd/amdgpu/amdgpu_res_cursor.h    |  97 +++++--
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h       |   7 +-
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c  | 259 ++++++++++--------
>>>>   4 files changed, 231 insertions(+), 133 deletions(-)
>>> <snip>
>>>
>>>> -/**
>>>> - * amdgpu_vram_mgr_virt_start - update virtual start address
>>>> - *
>>>> - * @mem: ttm_resource to update
>>>> - * @node: just allocated node
>>>> - *
>>>> - * Calculate a virtual BO start address to easily check if everything is CPU
>>>> - * accessible.
>>>> - */
>>>> -static void amdgpu_vram_mgr_virt_start(struct ttm_resource *mem,
>>>> -                                      struct drm_mm_node *node)
>>>> -{
>>>> -       unsigned long start;
>>>> -
>>>> -       start = node->start + node->size;
>>>> -       if (start > mem->num_pages)
>>>> -               start -= mem->num_pages;
>>>> -       else
>>>> -               start = 0;
>>>> -       mem->start = max(mem->start, start);
>>>> -}
>>>> -
>>>>   /**
>>>>    * amdgpu_vram_mgr_new - allocate new ranges
>>>>    *
>>>> @@ -366,13 +357,13 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>                                 const struct ttm_place *place,
>>>>                                 struct ttm_resource **res)
>>>>   {
>>>> -       unsigned long lpfn, num_nodes, pages_per_node, pages_left, pages;
>>>> +       unsigned long lpfn, pages_per_node, pages_left, pages, n_pages;
>>>> +       u64 vis_usage = 0, mem_bytes, max_bytes, min_page_size;
>>>>          struct amdgpu_vram_mgr *mgr = to_vram_mgr(man);
>>>>          struct amdgpu_device *adev = to_amdgpu_device(mgr);
>>>> -       uint64_t vis_usage = 0, mem_bytes, max_bytes;
>>>> -       struct ttm_range_mgr_node *node;
>>>> -       struct drm_mm *mm = &mgr->mm;
>>>> -       enum drm_mm_insert_mode mode;
>>>> +       struct amdgpu_vram_mgr_node *node;
>>>> +       struct drm_buddy *mm = &mgr->mm;
>>>> +       struct drm_buddy_block *block;
>>>>          unsigned i;
>>>>          int r;
>>>>
>>>> @@ -391,10 +382,9 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>                  goto error_sub;
>>>>          }
>>>>
>>>> -       if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
>>>> +       if (place->flags & TTM_PL_FLAG_CONTIGUOUS)
>>>>                  pages_per_node = ~0ul;
>>>> -               num_nodes = 1;
>>>> -       } else {
>>>> +       else {
>>>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>>                  pages_per_node = HPAGE_PMD_NR;
>>>>   #else
>>>> @@ -403,11 +393,9 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>   #endif
>>>>                  pages_per_node = max_t(uint32_t, pages_per_node,
>>>>                                         tbo->page_alignment);
>>>> -               num_nodes = DIV_ROUND_UP_ULL(PFN_UP(mem_bytes), pages_per_node);
>>>>          }
>>>>
>>>> -       node = kvmalloc(struct_size(node, mm_nodes, num_nodes),
>>>> -                       GFP_KERNEL | __GFP_ZERO);
>>>> +       node = kzalloc(sizeof(*node), GFP_KERNEL);
>>>>          if (!node) {
>>>>                  r = -ENOMEM;
>>>>                  goto error_sub;
>>>> @@ -415,9 +403,17 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>
>>>>          ttm_resource_init(tbo, place, &node->base);
>>>>
>>>> -       mode = DRM_MM_INSERT_BEST;
>>>> +       INIT_LIST_HEAD(&node->blocks);
>>>> +
>>>>          if (place->flags & TTM_PL_FLAG_TOPDOWN)
>>>> -               mode = DRM_MM_INSERT_HIGH;
>>>> +               node->flags |= DRM_BUDDY_TOPDOWN_ALLOCATION;
>>>> +
>>>> +       if (place->fpfn || lpfn != man->size)
>>>> +               /* Allocate blocks in desired range */
>>>> +               node->flags |= DRM_BUDDY_RANGE_ALLOCATION;
>>>> +
>>>> +       min_page_size = mgr->default_page_size;
>>>> +       BUG_ON(min_page_size < mm->chunk_size);
>>>>
>>>>          pages_left = node->base.num_pages;
>>>>
>>>> @@ -425,36 +421,61 @@ static int amdgpu_vram_mgr_new(struct ttm_resource_manager *man,
>>>>          pages = min(pages_left, 2UL << (30 - PAGE_SHIFT));
>>>>
>>>>          i = 0;
>>>> -       spin_lock(&mgr->lock);
>>>>          while (pages_left) {
>>>> -               uint32_t alignment = tbo->page_alignment;
>>>> -
>>>>                  if (pages >= pages_per_node)
>>>> -                       alignment = pages_per_node;
>>>> -
>>>> -               r = drm_mm_insert_node_in_range(mm, &node->mm_nodes[i], pages,
>>>> -                                               alignment, 0, place->fpfn,
>>>> -                                               lpfn, mode);
>>>> -               if (unlikely(r)) {
>>>> -                       if (pages > pages_per_node) {
>>>> -                               if (is_power_of_2(pages))
>>>> -                                       pages = pages / 2;
>>>> -                               else
>>>> -                                       pages = rounddown_pow_of_two(pages);
>>>> -                               continue;
>>>> -                       }
>>>> -                       goto error_free;
>>>> +                       pages = pages_per_node;
>>>> +
>>>> +               n_pages = pages;
>>>> +
>>>> +               if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
>>>> +                       n_pages = roundup_pow_of_two(n_pages);
>>>> +                       min_page_size = (u64)n_pages << PAGE_SHIFT;
>>>> +
>>>> +                       if (n_pages > lpfn)
>>>> +                               lpfn = n_pages;
>>>>                  }
>>>>
>>>> -               vis_usage += amdgpu_vram_mgr_vis_size(adev, &node->mm_nodes[i]);
>>>> -               amdgpu_vram_mgr_virt_start(&node->base, &node->mm_nodes[i]);
>>>> +               mutex_lock(&mgr->lock);
>>>> +               r = drm_buddy_alloc_blocks(mm, (u64)place->fpfn << PAGE_SHIFT,
>>>> +                                          (u64)lpfn << PAGE_SHIFT,
>>>> +                                          (u64)n_pages << PAGE_SHIFT,
>>>> +                                          min_page_size,
>>>> +                                          &node->blocks,
>>>> +                                          node->flags);
>>>> +               mutex_unlock(&mgr->lock);
>>>> +               if (unlikely(r))
>>>> +                       goto error_free_blocks;
>>>> +
>>>>                  pages_left -= pages;
>>>>                  ++i;
>>>>
>>>>                  if (pages > pages_left)
>>>>                          pages = pages_left;
>>>>          }
>>>> -       spin_unlock(&mgr->lock);
>>>> +
>>>> +       /* Free unused pages for contiguous allocation */
>>>> +       if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
>>>> +               u64 actual_size = (u64)node->base.num_pages << PAGE_SHIFT;
>>>> +
>>>> +               mutex_lock(&mgr->lock);
>>>> +               drm_buddy_block_trim(mm,
>>>> +                                    actual_size,
>>>> +                                    &node->blocks);
>>>> +               mutex_unlock(&mgr->lock);
>>>> +       }
>>>> +
>>>> +       list_for_each_entry(block, &node->blocks, link)
>>>> +               vis_usage += amdgpu_vram_mgr_vis_size(adev, block);
>>>> +
>>>> +       block = list_first_entry_or_null(&node->blocks,
>>>> +                                        struct drm_buddy_block,
>>>> +                                        link);
>>>> +       if (!block) {
>>>> +               r = -ENOENT;
>>>> +               goto error_free_res;
>>>> +       }
>>>> +
>>>> +       node->base.start = amdgpu_node_start(block) >> PAGE_SHIFT;
>>> Hmm, does this work? It looks like there are various places checking
>>> that res->start + res->num_pages <= visible_size, which IIUC should
>>> only return true when the entire object is placed in the mappable
>>> portion. i915 is doing something similar. Also it looks like
>>> ttm_resource_compat() is potentially relying on this, like when moving
>>> something from non-mappable -> mappable in
>>> amdgpu_bo_fault_reserve_notify()?
>>>
>>> Perhaps something like:
>>>
>>> if (vis_usage == num_pages)
>>>      base.start = 0;
>>> else
>>>      base.start = visible_size;
>>>
>>> Otherwise I guess just keep amdgpu_vram_mgr_virt_start()?
>>>
>> hmm, I wonder how it works, may be we didn't go through the corner case
>> where res->start + res->num_pages > visible_size
>>
>> in amdgpu if AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED flag is enabled, we
>> set the ttm_place.lpfn = visible_pfn at
>> amdgpu_bo_placement_from_domain(). Hence, in amdgpu_vram_mgr_new()
>> function DRM_BUDDY_RANGE_ALLOCATION flag is enabled, which calls the
>> alloc_range_bias() in drm_buddy.c.
>>
>> Here we get blocks chained together in random order complying
>> visible_pfn range. say for instance num_pages = 13
>> we may get,
>> Block 1 addr - 500 (order-3)
>> Block 2 addr - 400 (order-2)
>> Block 3 addr - 600 (order-0)
>>
>> I think currently base.start = Block 1 start address fetched from the
>> list and the address 500 assigned to it, which is good for the resource
>> access since we access the blocks using the list link
>>
>> But for the check res->start + res->num_pages <= visible_size in few
>> places, this doesn't work. AFAIK, keeping amdgpu_vram_mgr_virt_start()
>> doesn't work since the function looks for nodes in continuous address to
>> calculate the start address. AFAIK, assigning the start address (400 +
>> num_pages <= visible_size) mislead in our case since we use linked list
>>
>> how about replacing the check with a bool type return function which
>> checks the each block start address + block size <= visible_size?
> 
> Yeah, we already have that in the TTM code. It's just not used 
> everywhere IIRC.

Hi Christian,
here we have a problem, many places in ttm and amdgpu, we are using the
tbo->resource->start + bo->resource->num_pages operation, this doesn't
work in case of drm buddy since it allocates blocks in different
locations which are chained together using linked list.
> 
> The node->start can just be set to the invalid offset for now and should 
> be removed as soon as we don't need it any more.
Assigning the start block offset to resource->start doesn't work,
If we set node->start to invalid offset, we get an incorrect value?
> 
> Regards,
> Christian.