I have just got an Intel's DP55WB motherboard with i5 750 processor, SATA hard drive configured as IDE and 4 GB DDR3 RAM.

I have not been able to load either Ubuntu's 9.10 32-bit or 64-bit OS with the BIOS setting as "Active Processor Cores - ALL". I have to change it to "Active Processor Cores - 1".

With just one processor active, the installation is successful and I am able to use the system, however, all the other cores are not active. If I change the BIOS setting to Active Processor Cores - ALL, then it won't boot at all, just a cursor displayed after grub selection screen.

My kernel seems to support SMP and here is the output of
$ uname -a
Linux ubuntu 2.6.31-14-generic #48-Ubuntu SMP Fri Oct 16 14:05:01 UTC 2009

I could load Windows 7 RC without any problem and it runs with all the cores active. It also detected automatically when the BIOS setting changed to Active Processor Cores - ALL, as a kind of new devices detected (3 more CPUs detected) and after a restart, it is fine.

So how do I get SMP support and harness all the 4 cores of i5-750?
Is there better and easier support in Fedora? I have recently switched over from Fedora to Ubuntu. Thanks in advance.

Seems like it should work - see this phoronix review. Following pages show the cpuinfo output.

Thanks, it is reassuring to know that it should work. Here is the output of the
$ cat /proc/cpuinfo

processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 30
model name : Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz
stepping : 5
cpu MHz : 1197.000
cache size : 8192 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 1
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc up arch_perfmon pebs bts rep_good xtopology tsc_reliable nonstop_tsc pni dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt lahf_lm ida tpr_shadow vnmi flexpriority ept vpid
bogomips : 5333.54
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

Noticeable differences are
cpu MHz : 1197.000
cpu cores : 1

If enable all or 2 cores, then the machine just reboots, goes back to initial BIOS screen and stops. cpu MHz was initially high as soon as Ubuntu loaded, but later dropped to 1197.000.

Does it give any clue?
Should maxcpus be specified in the grub file, in grub2 menu.lst is not there and don't know how to do it.

cpu MHz problem is resolved by disabling dynamic processor voltage and clock changes in the BIOS. It is a nice feature actually and not a problem.

However, the problem of not being able to use more than one core still remains. I have even tried Fedora 11 x86_64 as well with a Live CD and the behaviour is exactly the same, it doesn't boot with more than one core enabled.

Posted about the problem in the Phoronix forum as well and hope to get some solution soon.

It was suggested to upgrade the BIOS and I have upgraded to the latest one. Still the same problem persists.

This problem is solved. I found the problem was caused by my old USB mouse. Replacing it with another new one solved this, strange it may sound. Now Ubuntu or Fedora (install DVD) boot with all the cores enabled.

I could also use all the cores with legacy USB support disabled in the BIOS, with the old mouse. However, this disables my keyboard till the OS is loaded i.e. can't choose grub menu options with this.

So the solution seems to be lying in having appropriate USB mouse.

Just wanted to drop in my 2 cents on this topic. I recently went through my bios on an ASUS M4A77D and mistakingly turned off ACPI support. The outcome of that caused the kernel to not see all of the cores my CPU offered. The fix of course involved just re-enabling ACPI support. I wanted to post this in case anyone else was stumped by having their multi-core CPU mysteriously turn into a single CPU. As always it was operator error..lol! I was trying to get my new motherboards onboard HD audio working on Ubuntu 9.10 x86-64 when all this happened. As it turns out you need to enable "Karmic-backports" in "Software Sources" and install 'linux-backports-modules-alsa-karmic-generic' to support the newer VIA ID 440 chip that my motherboard has. Hope this helps anyone solve that problem quicker than it took me.

Cheers!

I had to disabled apic in the grub menu otherwise only one core was activated 99% of the time.
Not always operator error some times it's OS error.