Wow!

Richard Guenther richard.guenther@gmail.com
Tue Jul 3 18:59:00 GMT 2007


On 7/3/07, Jeffrey Law <law@redhat.com> wrote:
> On Tue, 2007-07-03 at 13:07 +0200, Richard Guenther wrote:
> > On 7/3/07, Daniel Berlin <dberlin@dberlin.org> wrote:
> > > On 7/2/07, Uros Bizjak <ubizjak@gmail.com> wrote:
> > > > Daniel Berlin wrote:
> > > > > I'm curious if it was the pre/fre changes.  can you try -fno-tree-pre
> > > > > and -fno-tree-fre and see if it slows down again?
> > > > Adding -fno-tree-pre slows aermod back to 33.942s. Nice optimization. ;)
> > > Thanks.
> > > (You really should thank richard guenther and steven bosscher, who
> > > continually beat me up till i finished it :P)
> > >
> >
> > Unfortunately, this "improvement" is a miscompare:
> >
> > > Value= 2190.9357900     Target= 2191.1145000     Tolerance=0.10000000000E-02
> > FAIL <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > > Value= 34310.421880     Target= 34310.421880     Tolerance=0.30000000000E-01
> > > Value= 4260.5888700     Target= 4260.9716800     Tolerance=0.50000000000E-01
> > FAIL <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > > Value= 37093.921880     Target= 37094.375000     Tolerance=0.20000000000E-01
> > FAIL <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > > Value= 7924.6811500     Target= 7924.8842800     Tolerance=0.30000000000E-01
> > FAIL <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > > Value= 37093.921880     Target= 37094.375000     Tolerance= 1.0000000000
> >
> > aermod FAILED    4 fails and    2 passes
> Having been down this path so many times -- any time a benchmark shows
> a big improvement, my first reaction is that something has been mis-
> compiled.  If not, then I worry that it's just some ugly secondary
> cache effect from variables moving around on the stack or something
> similar.  Only once I can convince myself that neither of those is the
> case do I get excited about the improvement.
>
> Perhaps I've become somewhat jaded through the years :-)

Of course in this case (the above is with -ffast-math) one could say
I got what I asked for.  Fast but maybe (slightly) inaccurate.  Of course
we miss the tolerances by more than an order of magnitude.

Richard.



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