Karim BELABAS on Sun, 21 Sep 2003 13:01:41 +0200 (MEST)

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Re: performance comparison

On Sun, 21 Sep 2003, Igor Schein wrote:
> I ran nfgaloisconj(degree-92 pol) on 3 different platforms:
> Tru64 on 1GHz ev68 compiled with cc		99s
> Linux on 2.4GHz athlon compiled with gcc	220s
> Linux on 3.0GHz P4 compiled with gcc		302s
> I used --with-gmp for compilation of latest CVS sources and the
> initial stack was 256m.
> I can see 2 things here, that P4 does lose in comparison to Athlon,
> and that Alpha is a clear winner.  Am I correct in assuming that this
> is essentially a benchmark of floating point performance, where Alpha
> is way superior, or does Alpha's large cache play the role in the
> equation?   Or maybe gcc-vs-cc proposition is the factor here?
> In fact, I suspect that Pari's benches are dominated by integer
> arithmetic, making P4 the fastest platform, while most number field
> operations are floating point internsive.  Since number fields are
> bread-and-butter of Pari...

There's almost no (hardware) floating point arithmetic in PARI. Everything is
integer arithmetic.

What is true is that Pari's benches are dominated by _single precision_
integer arithmetic. With intensive multiprecision like the above, it makes
sense that the 64 bit machine outperforms the others. I would also assume
that cache size plays some (less important) role since most of the data is
connected with sequential access.

How does the above translate
1) without gmp ? [ my guess: alpha timings will be bad... ]
2) for smaller nfgaloisconj (possibly in a loop to get useful timings) ?
3) for a basic operation like

   p = 50000; default(realprecision, p);
   a = round(log(2)*10^p);
   b = a + 1;
   gettime(); for(i=1,100,a * b); gettime()

[ you'll be mostly profiling GMP here ! ]

3) Anything weird when profiling the above run ?


Karim Belabas                     Tel: (+33) (0)1 69 15 57 48
Dép. de Mathématiques, Bât. 425   Fax: (+33) (0)1 69 15 60 19
Université Paris-Sud              http://www.math.u-psud.fr/~belabas/
F-91405 Orsay (France)            http://www.parigp-home.de/  [PARI/GP]