sun x4500 and smp

[rondzierwa at comcast.net]

I am using a sunfire x4500 (thumper) with a pair of dual-core opteron 290 processors, running 10.1-RELEASE to serve up zfs filesystems via nfs and samba. 

The system reboots periodically when under load. I cannot find anything in any of the system logs that would account for why it rebooted, it just goes away for a while and comes back in a few minutes. 

Out of desperation, I tried disabling all but one of the processors. (hint.lapic.x.disabled=1 where x == 1, 2 and 3). Oddly enough the system doesn't reboot anymore. 

Is there any known issues about SMP not working on a sunfire x4500? I have searched the mail archives and haven't found anything useful. 

thanks in advance for any help or suggestions. 
ron.