2.6.27rc1 cannot boot more than 8CPUs

Jeff Chua
2008-08-06T03:15:41Z

I've a Dell R900 with 4 quad-core Xeon processors (total 16CPUs), but
can only managed to boot up with CONFIG_NR_CPUS=8. Setting
CONFIG_NR_CPUS=16 causes the kernel to hang while booting.

Here's the dmesg with CONFIG_NR_CPUS=8 ...

CPU6: Intel(R) Xeon(R) CPU L7345 @ 1.86GHz stepping 0b
checking TSC synchronization [CPU#0 -> CPU#6]: passed.
CPU 7 irqstacks, hard=c0526000 soft=c051e000
Booting processor 7/26 ip 6000
Initializing CPU#7
Calibrating delay using timer specific routine.. 3723.85 BogoMIPS (lpj=7447700)
CPU: L1 I cache: 32K, L1 D cache: 32K
CPU: L2 cache: 4096K
CPU: Physical Processor ID: 6
CPU: Processor Core ID: 2
x86 PAT enabled: cpu 7, old 0x7040600070406, new 0x7010600070106
CPU7: Intel(R) Xeon(R) CPU L7345 @ 1.86GHz stepping 0b
checking TSC synchronization [CPU#0 -> CPU#7]: passed.
Brought up 8 CPUs
Total of 8 processors activated (29790.71 BogoMIPS).
net_namespace: 596 bytes
Booting paravirtualized kernel on bare hardware
NET: Registered protocol family 16

Here's the dmesg with CONFIG_NR_CPUS=16 ...
Booting processor 8/1 ip 6000
Initializing CPU#8
Calibrating delay using timer specific routine.. 3723.85 BogoMIPS (lpj=7447793)
CPU: L1 I cache: 32K, L1 D cache: 32K
CPU: L2 cache: 4096K
CPU: Physical Processor ID: 0
CPU: Processor Core ID: 1
x86 PAT enabled: cpu 7, old 0x7040600070406, new 0x7010600070106
CPU8: Intel(R) Xeon(R) CPU L7345 @ 1.86GHz stepping 0b
checking TSC synchronization [CPU#0 -> CPU#8]: passed.
*** Hangs here ***

How can I debug this further? I'm using the latest linux git pull.

Thanks,
Jeff.