[Intel-gfx] [PATCH 2/2] drm/i915: Use remap_pfn_range() to prefault all PTE in a single pass

[Volkin, Bradley D]

On Tue, Jun 10, 2014 at 04:14:41AM -0700, Chris Wilson wrote:
> On an Ivybridge i7-3720qm with 1600MHz DDR3, with 32 fences,
> Upload rate for 2 linear surfaces:  8134MiB/s -> 8154MiB/s
> Upload rate for 2 tiled surfaces:   8625MiB/s -> 8632MiB/s
> Upload rate for 4 linear surfaces:  8127MiB/s -> 8134MiB/s
> Upload rate for 4 tiled surfaces:   8602MiB/s -> 8629MiB/s
> Upload rate for 8 linear surfaces:  8124MiB/s -> 8137MiB/s
> Upload rate for 8 tiled surfaces:   8603MiB/s -> 8624MiB/s
> Upload rate for 16 linear surfaces: 8123MiB/s -> 8128MiB/s
> Upload rate for 16 tiled surfaces:  8606MiB/s -> 8618MiB/s
> Upload rate for 32 linear surfaces: 8121MiB/s -> 8128MiB/s
> Upload rate for 32 tiled surfaces:  8605MiB/s -> 8614MiB/s
> Upload rate for 64 linear surfaces: 8121MiB/s -> 8127MiB/s
> Upload rate for 64 tiled surfaces:  3017MiB/s -> 5127MiB/s
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

The translation from vm_insert_pfn to remap_pfn_range looks correct. I don't know
these APIs particularly well though. I wonder if there's any reason it would be
unsafe to call remap_pfn_range from .fault() since it seems to only be used in
.mmap() handlers in other places. Reading their implementations, nothing jumped
out, so I'll say

Reviewed-by: Brad Volkin <bradley.d.volkin at intel.com>

with the note that you may want to take a look just in case.

> ---
>  drivers/gpu/drm/i915/i915_gem.c | 28 +++++++++++++---------------
>  1 file changed, 13 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index e1f68f06c2ef..7128d389a6ff 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1709,21 +1709,19 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  	pfn >>= PAGE_SHIFT;
>  
>  	if (!obj->fault_mappable) {
> -		int i;
> -
> -		for (i = 0; i < obj->base.size >> PAGE_SHIFT; i++) {
> -			ret = vm_insert_pfn(vma,
> -					    (unsigned long)vma->vm_start + i * PAGE_SIZE,
> -					    pfn + i);
> -			if (ret)
> -				break;
> -		}
> -
> -		obj->fault_mappable = true;
> -	} else
> -		ret = vm_insert_pfn(vma,
> -				    (unsigned long)vmf->virtual_address,
> -				    pfn + page_offset);
> +		ret = remap_pfn_range(vma,
> +				      vma->vm_start,
> +				      pfn,
> +				      obj->base.size,
> +				      vma->vm_page_prot);
> +		obj->fault_mappable = ret == 0;
> +	} else {
> +		ret = remap_pfn_range(vma,
> +				      (unsigned long)vmf->virtual_address,
> +				      pfn + page_offset,
> +				      PAGE_SIZE,
> +				      vma->vm_page_prot);
> +	}
>  unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  unlock:
> -- 
> 2.0.0
> 
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