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

[Theiss, Ingo]

Am Freitag, 11. November 2011 14:33 CET, Michel Dänzer <michel at daenzer.net> schrieb: 
 
> 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...

Ok I have added -mfpmath=sse to the 32-bit CFLAGS and the readback performance increased from 30.44 Mpixels/sec to 48.92 Mpixel/sec. We are getting closer to the 64-bit performance.

Next I try to find out what Brian has asked for ... 

Thanks so far!

Regards,

Ingo