Re: [PATCH 2/2] drm/i915: Do not force non-caching copies for pwrite along shmem path

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Mar 07, 2014 at 08:30:37AM +0000, Chris Wilson wrote:
> We don't always want to write into main memory with pwrite. The shmem
> fast path in particular is used for memory that is cacheable - under
> such circumstances forcing the cache eviction is undesirable. As we will
> always flush the cache when targeting incoherent buffers, we can rely on
> that second pass to apply the cache coherency rules and so benefit from
> in-cache copies otherwise.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Do you have some numbers on this? Looks good otherwise.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_gem.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 877afb2c576d..e0ca6d6be2ae 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -810,9 +810,8 @@ shmem_pwrite_fast(struct page *page, int shmem_page_offset, int page_length,
>  	if (needs_clflush_before)
>  		drm_clflush_virt_range(vaddr + shmem_page_offset,
>  				       page_length);
> -	ret = __copy_from_user_inatomic_nocache(vaddr + shmem_page_offset,
> -						user_data,
> -						page_length);
> +	ret = __copy_from_user_inatomic(vaddr + shmem_page_offset,
> +					user_data, page_length);
>  	if (needs_clflush_after)
>  		drm_clflush_virt_range(vaddr + shmem_page_offset,
>  				       page_length);
> -- 
> 1.9.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch