Re: [Mesa3d-dev] dynamic code generation with gcc

[Josh V. <ho...@na...>]

"Stephen J Baker" <sj...@li...> writes:

> If it's for something like varying the Z buffer depth - then a large
> overhead might be acceptable (although I still maintain that creating
> a dependence on a C compiler is a disasterously bad decision).

I just want to make sure there isn't a misunderstanding here - the C
compiler would only be used to compile special case functions.  There
would always be a generic fallback, so Mesa would work (although more
slowly) even without a compiler installed.

> If it's something like catering for a particular combination of (say)
> blend mode, texture type, dither and fogging (the kind of thing that
> the SGI OpenGL-for-Windoze appears to do) - then taking even a couple
> of milliseconds at runtime when you first happen to see a polygon with
> that combination of states would be completely unacceptable - even with
> caching.

If it was just 20 milliseconds or so, I doubt most users would notice.
The problem is, I can easily see the delay being 500 ms for a big
function.

I can think of two workarounds:

1. Make the cache persistent, then the delay would only happen the
   first time you run your application.

2. Run the compiler in the background at low priority (say 10% cpu).
   You would have to make do with the generic fallback until the
   compile completes, but there wouldn't be a 'hitch' when the
   application exposes a different path.

Do you think that would be acceptable?

Josh