[Mesa-dev] Performance glxSwapBuffers 32 bit vs. 64 bit

[Michel Dänzer]

On Fre, 2011-11-11 at 14:15 +0100, Theiss, Ingo wrote: 
> Am Freitag, 11. November 2011 12:09 CET, Michel Dänzer <michel at daenzer.net> schrieb: 
> 
> > So It makes sense to find a glReadPixels in VirtualGL's glxSwapBuffers.
> > 
> > Ah. I thought the time measurements in Ingo's original post were for the
> > Mesa glXSwapBuffers, not the VirtualGL one. If it's the latter, then
> 
> > this makes sense.
> > 
> > Ingo, I noticed that your 64-bit and 32-bit drivers were built from
> > slightly different Git snapshots. Is the problem still the same if you
> > build both from the same, current snapshot?
> > 
> > If yes, have you compared the compiler flags that end up being used in
> > both cases? E.g., in 64-bit mode SSE is always available, so there might
> > be some auto-vectorization going on in that case.
> 
> I´ve rebuild my 64-bit and 32-bit drivers from a fresh Git snapshot
> and turned on all processor optimizations in both builds.
> But nevertheless the readback performance measured inside VirtualGL is
> only half of the 64-bit readback performance and of course the
> rendered window sceene is noticeable slower to :-( 
> 
> Here are the compiler flags used.
> 
> 32-bit:
> 
> CFLAGS: -O2 -Wall -g -m32 -march=amdfam10 -mtune=amdfam10 -fno-omit-frame-pointer -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fno-builtin-memcmp -m32 -O2 -Wall -g -m32 -march=amdfam10 -mtune=amdfam10 -fno-omit -frame-pointer -fPIC -m32

Have you tried adding -mfpmath=sse to the 32-bit CFLAGS? According to my
gcc documentation, that option is enabled by default in 64-bit mode but
disabled in 32-bit mode.

Anyway, I guess there's room for optimization in glReadPixels...


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer