Re: [Intel-gfx] [PATCH] drm/i915/ttm: consider all placements for the page alignment

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 6/22/21 2:15 PM, Matthew Auld wrote:
> On Tue, 22 Jun 2021 at 11:11, Thomas Hellström
> <thomas.hellstrom@linux.intel.com> wrote:
>>
>> On 6/22/21 11:58 AM, Matthew Auld wrote:
>>> Just checking the current region is not enough, if we later migrate the
>>> object somewhere else. For example if the placements are {SMEM, LMEM},
>>> then we might get this wrong. Another idea might be to make the
>>> page_alignment part of the ttm_place, instead of the BO.
>>>
>>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
>>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 21 ++++++++++++++++++++-
>>>    1 file changed, 20 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> index c5deb8b7227c..5d894bba6430 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
>>> @@ -753,6 +753,25 @@ void i915_ttm_bo_destroy(struct ttm_buffer_object *bo)
>>>                call_rcu(&obj->rcu, __i915_gem_free_object_rcu);
>>>    }
>>>
>>> +static u64 i915_gem_object_page_size(struct drm_i915_gem_object *obj)
>>> +{
>>> +     u64 page_size;
>>> +     int i;
>>> +
>>> +     if (!obj->mm.n_placements)
>>> +             return obj->mm.region->min_page_size;
>>> +
>>> +     page_size = 0;
>>> +     for (i = 0; i < obj->mm.n_placements; i++) {
>>> +             struct intel_memory_region *mr = obj->mm.placements[i];
>>> +
>>> +             page_size = max_t(u64, mr->min_page_size, page_size);
>>> +     }
>>> +
>>> +     GEM_BUG_ON(!page_size);
>>> +     return page_size;
>>> +}
>>> +
>>>    /**
>>>     * __i915_gem_ttm_object_init - Initialize a ttm-backed i915 gem object
>>>     * @mem: The initial memory region for the object.
>>> @@ -793,7 +812,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
>>>        obj->base.vma_node.driver_private = i915_gem_to_ttm(obj);
>>>        ret = ttm_bo_init(&i915->bdev, i915_gem_to_ttm(obj), size,
>>>                          bo_type, &i915_sys_placement,
>>> -                       mem->min_page_size >> PAGE_SHIFT,
>>> +                       i915_gem_object_page_size(obj) >> PAGE_SHIFT,
>> Hmm, can't we just have the buddy manager silently enforce its
>> min_page_size?
> Maybe, but we need some way of overriding it for all of our page-table
> allocations(and some other stuff also), so being able to control the
> page_alignment at the object level here seems reasonable? Could maybe
> pass it through with create_lmem_with_page_size(..., page_size)? Ok,
> it might be best to first type it and then see how it will all fit
> together.
>
Hmm, OK, I'm not 100% sure what the various requirements are here on the 
object level. But for region requirements, I think we've historically 
enforced that through the manager, taking also the bo->page_alignment 
into account and applying the larger of the two,

There is an example in vmw_thp_insert_aligned().

/Thomas


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