Pg on SMP half-powered

Hello, hackers!

I am running postgresql 7.1 on a SMP Linux box. It runs, but it never pass a 
loadavg of 0.4, no matter how I try to overload the system.
The same configuration, the same executable, the same test on a non-SMP 
machine gives a loadavg of 19.
That means that a Xeon SMP box with 1Gb of RAM goes slowlier than a weak 
CPU, with the same postgres, the same configuration, and the same test.
Anybody knows what is happening? Is there something to do on a SMP machine 
for it to run? I tried with lots of shared memory, and with "commit_delay=0", 
but nothing worked.
Yours: