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Re: Haney's real matrix test regression


Hi Peter!

pete@ltoi.iap.physik.tu-darmstadt.de wrote:

> Hello ...
>
> yesterday i was not here in the office / at my E-mail account;
> and i haven't read the gcc-mailing list yet. Thus i currently don't
> know, if this is "urgent" anymore:

Well, in the meanwhile I could establish beyond any reasonable doubt that it is not
"simply" a question of partial register stalls, therefore an AMD test (vs any other
x86 check) is not strictly necessary anymore :-)
Have a look at:

    http://gcc.gnu.org/ml/gcc/2001-10/msg01314.html

It is obvious that the innermost loop, that over i, the most important one, is
*much* smaller and faster for gcc3.0.2 (or 3.1 of just a week ago... :-(

> > My i686 is in fact a PII: perhaps someone may run "Haney Speed" built with
> > today's 3.1 on an AMD core to exclude quickly the possibility of another nasty
> > partial register stall???
>
> Hm, up to my knowledge, the AMD Athlon didn't suffer (at least that much)
> from partial register stalls (??) Athlon suffers from the higher latencies
> of the VIA (or VIA alike AMD) chipsets (Why is VIA-KT266A faster
> than KT266 ?) and his small TLB's.

If you are curious about PRS, I learned all I know about those (prompted by Richard
Henderson) from the docs available from:

    http://www.agner.org/assem/

> Anyway, currently there is no gcc-3.1 installed on my system(s). Any
> suggestions for a recommended version, that builds clean on a i686 (binutils
> 2.9.1.0.xx in /usr/bin/ & 2.11.2 in /usr/local/bin) and a i586-system
> (binutils 2.9.1.0.xx only at the moment)?
>
> Peter Schorsch

Recently, I have started keeping my trees updated using CVS, but I'm seeing that a
snapshot sufficiently recent (which should display clearly the problem) is
available from gcc.gnu.org:

    gcc.gnu.org:/pub/gcc/snapshots/2001-10-23

Thank you very much Peter!
Such sudden performance regression make me crazy!

Cheers,
Paolo.




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