dual opteron only one cpu in top & gnome-system-monitor?

[Ralf Sigmund]

installing fedora rawhide x86_64 on a 2 cpu opteron system there is only 
one cpu listed in top:

> top - 11:17:35 up 23:14,  3 users,  load average: 0.00, 0.02, 0.03
> Tasks:  62 total,   1 running,  61 sleeping,   0 stopped,   0 zombie
> Cpu(s):  0.0% us,  0.2% sy,  0.0% ni, 99.8% id,  0.0% wa,  0.0% hi,  
> 0.0% si
> Mem:   6031516k total,  5280512k used,   751004k free,   137000k buffers
> Swap:  2040244k total,        0k used,  2040244k free,  4688688k cached

cpuinfo shows both cpus:

[sigmund at pdw-74 /tmp]$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 5
model name      : AMD Opteron(tm) Processor 246
stepping        : 8
cpu MHz         : 1994.059
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext lm 3dnowext 3dnow
bogomips        : 3940.35
TLB size        : 1088 4K pages
clflush size    : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts ttp
 
processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 5
model name      : AMD Opteron(tm) Processor 246
stepping        : 8
cpu MHz         : 1994.059
cache size      : 1024 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext lm 3dnowext 3dnow
bogomips        : 3981.31
TLB size        : 1088 4K pages
clflush size    : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts ttp