[PATCH v3 5/5] drm: Add TODO item for optimizing format helpers

[Sam Ravnborg]

On Wed, Feb 23, 2022 at 08:38:04PM +0100, Thomas Zimmermann wrote:
> Add a TODO item for optimizing blitting and format-conversion helpers
> in DRM and fbdev. There's always demand for faster graphics output.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  Documentation/gpu/todo.rst | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> index 7bf7f2111696..7f113c6a02dd 100644
> --- a/Documentation/gpu/todo.rst
> +++ b/Documentation/gpu/todo.rst
> @@ -241,6 +241,28 @@ Contact: Thomas Zimmermann <tzimmermann at suse.de>, Daniel Vetter
>  
>  Level: Advanced
>  
> +Benchmark and optimize blitting and format-conversion function
> +--------------------------------------------------------------
> +
> +Drawing to dispay memory quickly is crucial for many applications'
              display
> +performance.
> +
> +On at least x86-64, sys_imageblit() is significantly slower than
   On, at least x86-64, ...
   To me the extra comma makes sense, but grammar is not my strong side.
 
> +cfb_imageblit(), even though both use the same blitting algorithm and
> +the latter is written for I/O memory. It turns out that cfb_imageblit()
> +uses movl instructions, while sys_imageblit apparently does not. This
> +seems to be a problem with gcc's optimizer. DRM's format-conversion
> +heleprs might be subject to similar issues.
   helpers
> +
> +Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion
> +helpers. In cases that can be further optimized, maybe implement a different
> +algorithm, For micro-optimizations, use movl/movq instructions explicitly.
   algorithm. (period, not comma)
> +That might possibly require architecture specific helpers (e.g., storel()
> +storeq()).
> +
> +Contact: Thomas Zimmermann <tzimmermann at suse.de>
> +
> +Level: Intermediate

With the small fixes above:
Acked-by: Sam Ravnborg <sam at ravnborg.org>

Another option would be to re-implement imageblit() to be drm specific.
Maybe we can then throw out some legacy code and optimize only for the drm
use. And then maybe only a small part of the code would differ if this
is I/O memory or direct accessible memory.

	Sam