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Re: Perfomance regression
On Tuesday 05 April 2005 09:13, Jerry DeLisle wrote:
> Steve Kargl wrote:
> >>Does anybody have ideas what can affect performance of attached test in
> >>these conditions?
> >
> > Disable hyperthreading. It's a piece of crap, but probably
> > isn't important here.
> >
> > Is this code integer or floating point intensive?
> >
> >>From what I know about xeon cpu's, you should have bought opteron.
I agree with you of course, opteron rules ;-) But I don't think
hyperthreading is to blame here.
(Did you know, btw, that the intel compilers can use hyperthreading
for dynamic prefetching? It can be used for interesting things like
that...)
> Need to instrument the sample.f program and see if the computed results
> are the same for g77 and gfortran. The sample program has some long
> complicated expressions with many continuation lines. Might be hitting
> a limit on string length of the expressions, or the optimizers are just
> not handling it.
It could very well be a register presure issue or something like
that, if you have really large expressions. We have this problem
in SPECfp mgrid as well. In a very large expression, we move a
lot of loop invariant code out of inner loops in the tree passes,
only to find out that your whopping 6 registers on x86 are simply
not enough.
It would be great if you can find out which subprogram is slowed
down the most, and can create a test case from it...
Gr.
Steven