[webkit-dev] Transformations precision: double -> float

[Benjamin Poulain]

On Mon, Oct 15, 2012 at 9:35 AM, Gabor Rapcsanyi <rgabor at inf.u-szeged.hu>wrote:

>  On 10/12/2012 11:23 AM, Tom Hudson wrote:
>
> Do you have particular bottleneck functions that you have reason to
> believe would benefit from ARM SIMD optimizations? Under what
> workloads, and how much benefit?
>
> We've see a few ridiculously expensive transform functions in WebKit
> that my colleagues in Chapel Hill might be able to recall, but usually
> it's the rendering engines that are hot, not WebKit itself.
>
>  Yes, you're right that the rendering engine is usually the basic
> bottleneck,
> but why shouldn't we optimize WebKit where it is possible.
> For example the function what you asking is
> TransformationMatrix::multiply().
> I made a test which could be speed up with optimizing this matrix
> multiplication.
> I uploaded here: https://bugs.webkit.org/show_bug.cgi?id=98913
>

You are suggesting a massive change to WebKit based on an hypothetical
universe in which a certain function is important.
The problem is the same claim can be done for about any function of WebKit.
You can handcraft a microbenchmark exercising a slow function and redesign
everything to make that particular function fast. Does this add a lot of
value to the project? No so much.

As much as I am in favor of increasing the use of SIMD, especially on ARM,
I am really not a fan of the idea of switching to float on such weak
premises.

Benjamin
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