Let's use gcc-4.2, not 4.1 -- OpenMP
Stefan Ehmann
shoesoft at gmx.net
Sun Dec 17 08:11:05 PST 2006
On Sunday 17 December 2006 15:44, Ulrich Spoerlein wrote:
> David O'Brien wrote:
> > On Fri, Dec 15, 2006 at 07:14:53PM +0100, Stefan Ehmann wrote:
> > > > CPU: AMD Athlon(TM) XP 2700+ (2166.44-MHz 686-class CPU)
> >
> > ..
> >
> > > Settings/Compiler | gcc-3.4 | gcc-4.1 | gcc-4.2
> > > ----------------------------+---------+---------+---------
> > > -O2 | 6.46s | 6.67s | 6.38s
> > > -O2 -funroll-loops | 4.44s | 4.16s | 4.02s
> > > -O2 -march=athlon-xp -fun.. | 4.39s | 4.38s | 4.26s
> > > -O3 | 6.14s | 5.23s | 5.16s
> > > -O3 -funroll-loops | 4.24s | 4.87s | 4.95s
> > > -O3 -march=athlon-xp -fun.. | 4.19s | 4.90s | 5.07s
> >
> > A fine example that -O3 isn't always better than -O2.
> > I wonder if you're blowing the L2 cache. IIRC, all Athlon XP 2700+
> > are the Thoughbread core, which has only 256KB L2.
>
> I'd be very much interested in -Os numbers. It should help with the
> cache ...
While -Os -funroll-loops seems a weird combination:
Settings/Compiler | gcc-3.4 | gcc-4.1 | gcc-4.2
----------------------------+---------+---------+---------
-Os | 6.96s | 6.48s | 6.69s
-Os -funroll-loops | 5.01s | 4.63s | 4.58s
-Os -march=athlon-xp -fun | 4.93s | 4.69s | 4.64s
We probably should stop exploiting my simple test or perform it properly if
there's really any interest (e.g. larger number of programs, different CPUs,
something better than time(1); also my computer was up to 0.05s slower than
on Friday :-))
Also, for most "normal" programs, there won't be that much difference between
compilers and/or settings.
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