Re: 2.6.32.1 kernel configuration only seeing 1 core on Intel E5540 CPU

Carsten Aulbert wrote:
> Hi Kurt
> 
> On Thursday 24 June 2010 00:53:46 Kurt Newman wrote:
>> I've loaded this same i7 Nehalem machine with CentOS 5.3
>> (2.6.18-128.el5PAE), Ubuntu 9.04 (2.6.28-11-generic), and a modified
>> distro with a custom kernel (2.6.32.1).
>>
>> The CentOS and Ubuntu kernels find all 4 cores just fine; however, my
>> custom kernel only finds 1.  I've enabled the following:
>>
>>  - SMP
>>  - X86_BIGSMP (systems with more than 8 cpus)
>>  - X86_EXTENDED_PLATFORM (extended x86 platform)
>>  - SCHED_SMT (hyper-threading)
>>  - SCHED_MC (Multi-core scheduler)
>>  - and varied between M686 (Pentium Pro) and MCORE2 (newer Xeon)
> 
> Just guessing, but could the CentOS and Ubuntu Kernel be a 64bit variant, 
> while your custom one is 32bit? (also .1 is heavily outdated .15 is the 
> current which apparently fixes several bugs).
> 
> I've not been using 32bit kernel for a couple of years and never with a multi-
> core system thus just poking into the dark here.


Just to follow up.  The solution was that I needed to enable Power
Management and ACPI.  Apparently newer machines require it (e.g.
hyper-threading or IA64).

Read http://tldp.org/HOWTO/Battery-Powered/powermgm.html#HYPERTHREAD for
more information.