CPU being treated as single core since upgrading to Ubuntu 11.10

[jayhat]

I've noticed performance issues since upgrading to 11.10, and out of curious I checked /proc/cpuinfo to find this:


processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 26
model name : Intel(R) Xeon(R) CPU W3520 @ 2.67GHz
stepping : 5
cpu MHz : 2666.352
cache size : 8192 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 1

That CPU is quad-core, but Ubuntu appears to be treating it as single core. It may have always been treated this way, with the performance regression being related to unity, however I doubt this.

Anyone have this same CPU?
Is this a known issue?
If not, anyone have any suggestions on where to start looking?

Thanks


Edit:
It's a stock standard Dell T3500 and I've checked the BIOS settings: 'support multiple cores' is enabled.

[jayhat]

Solved, needed to get grub to force acpi. No idea why this changed recently.