Re: [PATCH 09/21] drm/i915: align 64K objects to 2M

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Fri, 2017-09-29 at 17:10 +0100, Matthew Auld wrote:
> We can't mix 64K and 4K pte's in the same page-table, so for now we
> align 64K objects to 2M to avoid any potential mixing. This is
> potentially wasteful but in reality shouldn't be too bad since this only
> applies to the virtual address space of a 48b PPGTT.
> 
> v2: don't separate logically connected ops
> 
> Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

<SNIP>

> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -501,9 +501,18 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
>  		if (upper_32_bits(end) &&
>  		    vma->page_sizes.sg > I915_GTT_PAGE_SIZE) {

Here. See below.

>  			u64 page_alignment =
> -				rounddown_pow_of_two(vma->page_sizes.sg);
> +				rounddown_pow_of_two(vma->page_sizes.sg |
> +						     I915_GTT_PAGE_SIZE_2M);
>  
>  			alignment = max(alignment, page_alignment);
> +
> +			/*
> +			 * We can't mix 64K and 4K PTEs in the same page-table (2M
> +			 * block), and so to avoid the ugliness and complexity of
> +			 * coloring we opt for just aligning 64K objects to 2M.
> +			 */

This is about size, the alignment is happening above, I'd lift the
comment there.

> +			if (vma->page_sizes.sg & I915_GTT_PAGE_SIZE_64K)
> +				size = round_up(size, I915_GTT_PAGE_SIZE_2M);
>  		}

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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