On Sun, 2004-10-10 at 22:57, Bryan J. Smith wrote:
> On Sun, 2004-10-10 at 20:50, Robert Snyder wrote:
> > Slack is fast and nimble. But noticed with some applications the
> > extra optimaztion that are targeted for my Pentium 4 processor Seem
> > to make a difference. With near identical setups between gentoo and
> > slackware I noticing better Frames per sec in games. Large emulation
> > products such as Basilisk II , SheepShaver and PearPC are snappier in
> > there functions. All I was saying that thing felt snappier, saying
> > something felt is far for sciencific benchmarks
>
> Ah, yes, the gcc -O3 option must be used then.
> That will liberally use SSE instead of the FPU.
>
> I'd take a look at the "accuracy" of those optimizations.
> Because the P3/P4 have dedicated SSE pipes.
> Those pipes do not offer the accuracy and precision of the FPU.
>
> In a nutshell, they weren't designed with accuracy or precision in mind,
> but performance.
> That means they were purposely engineered with "lossy math."
>
> Tom's hardware guide was the first one to discover this years ago.
> Comparing SSE to FPU MPEG-4 image quality, it was signficiant.
>
> _All_ floating point math in a CPU is error-prone.
> But the difference between x87 FPU and P3+ SSE are radically different.
> The former, we're talking 16+ digits down.
> With the latter, we could be talking very significant errors.
>
> All done on _purpose_.
>
> -- Bryan
>
> P.S. Athlons/Opterons use their used FPU pipes for SSE operations --
> i.e., no loss of accuracy or precision.
I dont see it passing any -O3 commands to the compilier. As I watch it
go passing by.
The defualt cflags for Portage when compiling are "-O2 -march=pentium4
-fomit-frame-pointer" Now I have noticed when using a gui front end like
porthole that at the bottom they do list additional flags that the
piticular ports mantainer decided to use extra usually you see thing
like mmx and sse flags but never seen the -O3
Last time i had use an -O3 flag it was after i tricked ICC 7 to install
on slackware and got it setup and use ICC 7 with the -O3 -march=pentium4
to get some usualable speed out of sheepshaver when it first came out
with it retrofitted powerpc emulation engine. As some would forget that
Sheepshaver started out as a ppc virtual machine for Be Boxes and PPC
macs running BeOS and then a ported to ppc linux then after couple of
years just stitting there in a lonely cvs a ppc emulation core was
straped to it and some code changes made and then it became the first
PPC emulation on X86 platform.
But things are stable and "FEEL" slightly faster. I will emphansize
"FEEL" because I have no hard proof that it is faster.
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