[PATCH 6/6] drm/amdgpu: use more than 64KB fragment size if possible

[Jay Cornwall]

On 2016-08-09 07:52, Christian König wrote:
> From: Christian König <christian.koenig at amd.com>
> 
> We align to 64KB, but when userspace aligns even more we can easily use 
> more.
> 
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index e6c030b..88f4109 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -817,13 +817,13 @@ static void amdgpu_vm_frag_ptes(struct
> amdgpu_pte_update_params	*params,
>  	 * allocation size to the fragment size.
>  	 */
> 
> -	/* SI and newer are optimized for 64KB */
> -	uint64_t frag_flags = AMDGPU_PTE_FRAG(AMDGPU_LOG2_PAGES_PER_FRAG);
> -	uint64_t frag_align = 1 << AMDGPU_LOG2_PAGES_PER_FRAG;
> +	const uint64_t frag_align = 1 << AMDGPU_LOG2_PAGES_PER_FRAG;
> 
>  	uint64_t frag_start = ALIGN(start, frag_align);
>  	uint64_t frag_end = end & ~(frag_align - 1);
> 
> +	uint32_t frag;
> +
>  	/* system pages are non continuously */
>  	if (params->src || params->pages_addr || !(flags & AMDGPU_PTE_VALID) 
> ||
>  	    (frag_start >= frag_end)) {
> @@ -832,6 +832,10 @@ static void amdgpu_vm_frag_ptes(struct
> amdgpu_pte_update_params	*params,
>  		return;
>  	}
> 
> +	/* use more than 64KB fragment size if possible */
> +	frag = lower_32_bits(frag_start | frag_end);
> +	frag = likely(frag) ? __ffs(frag) : 31;
> +
>  	/* handle the 4K area at the beginning */
>  	if (start != frag_start) {
>  		amdgpu_vm_update_ptes(params, vm, start, frag_start,
> @@ -841,7 +845,7 @@ static void amdgpu_vm_frag_ptes(struct
> amdgpu_pte_update_params	*params,
> 
>  	/* handle the area in the middle */
>  	amdgpu_vm_update_ptes(params, vm, frag_start, frag_end, dst,
> -			      flags | frag_flags);
> +			      flags | AMDGPU_PTE_FRAG(frag));
> 
>  	/* handle the 4K area at the end */
>  	if (frag_end != end) {

Would this change not direct larger fragments away from the BigK TLB 
partition?

My understanding was VM_L2_CNTL3.L2_CACHE_BIGK_FRAGMENT_SIZE is an exact 
match and not a minimum size. I can't find any immediate documentation 
on that topic to confirm.

-- 
Jay Cornwall