[Mesa-dev] [PATCH] softpipe: Take all lods into account when texture sampling.

[Roland Scheidegger]

On 06/21/2012 08:30 AM, Olivier Galibert wrote:
> On Wed, Jun 20, 2012 at 01:44:14PM +0100, Roland Scheidegger wrote:
>> A lot of code I just glossed over it, but seems to look ok other than
>> the (performance) implications this might have.
>
> Actually whether there's a performance implication is not obvious.  In
> practice the code just kicks the 4-pixel loop one or two function
> calls higher.  This unshares some tests, some function calls, and the
> mip-size computation shifts.  For normal texturing and on x86 the
> tests are correctly predicted after the first one, and so are the
> function calls, giving all of them a near zero cost.  So I'm not sure
> the costs is that measurable.
Well I'm not sure neither, that's why I'd have liked to see some number, 
even if it's just from multiarb :-) It's not just about prediction 
though, e.g. your indirect address lookups might be simpler when 
unrolled due to using immediates instead of index register etc.
I can live without that number, though...

>
> With the actual vectorization the llvmpipe situation may be different
> (not so sure with the aos texturing though).
Yes the additional lookups for the mip level base addresses are going to 
hurt (slightly), and the min/mag
filter selection is going to be a big mess (both aren't really dependent 
on aos/soa texturing). This is really going to need a different path.

Roland