Re: kernel unable to use more than 2 of 16 CPUs on IntelE5540 (i7)

From: Kurt Newman
Date: Fri Jun 25 2010 - 17:49:14 EST

Roland Dreier wrote:
> Your config seems to have CONFIG_PM and therefore CONFIG_ACPI disabled.
> So the kernel is relying on mptable information. Unsurprisingly on a
> modern system, that info is probably broken -- since everything would
> have been tested with ACPI.
> Try turning on CONFIG_ACPI and see if that helps at all.

Turning on ACPI solved the problem. I don't understand why ACPI needs
to be turned on, but after reading the power management ldp it confirms
what you said. I just didn't think that this would have mattered.

Thanks for the help,

For anyone else with this problem, here's something to read:

Some SMP system manufacturers may have omitted the pre-ACPI tables used
for SMP configurations. In this case, ACPI is required.

If you have a newer system that supports Hyper-Threading, you will need
to enable ACPI (and, of course, SMP). Without it, your Linux system may
be unable to discover and initialize all of the virtual processors.

IA64 machines require ACPI as well. Additionally, NUMA servers are
starting to require it for proper initialization.

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