ubuntu - Second CPU missing of Dual Core

07
2014-07
  • Zardoz

    My Lenovo T61 has a dual core CPU. I just noticed that under Ubuntu 10.10 only one CPU is recognized. I know that once both CPUs worked. Not sure since when the second CPU is missing. Maybe since the last kernel update. Currently I am using linux-image-2.6.35-23-generic (for x86_64).

    What can I do to enable the second CPU again?

    Here the ouput of /proc/cpuinfo

    processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 23
model name : Intel(R) Core(TM)2 Duo CPU T8100 @ 2.10GHz
stepping : 6
cpu MHz : 800.000
cache size : 3072 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 1
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 lahf_lm ida dts tpr_shadow vnmi flexpriority
bogomips : 4189.99
clflush size : 64
cache_alignment : 64
address sizes : 36 bits physical, 48 bits virtual
power management:

    Any help is welcome. I really need that CPU power for my work here.

    • Answers
  • Zardoz

    The current Nvidia driver (the one from Nvidia itself "NVIDIA-Linux-x86_64-260.19.21") leads to those problems. After uninstalling it and installing the one of Ubuntu again the second CPU shows up again. Not sure why that driver has this problem, but I will test things a bit further when I have the time.

  • Malcolm

    I noticed that I had this problem right after I performed

        sudo pm-powersave true

    I inverted it, restarted, and my laptop now recognizes my 2 cpus. (For completeness...)

       sudo pm-powersave false

    I performed this on:

    MacbookPro 5,2

    Ubuntu 12.04 LTS

    Intel Core 2 Duo

  • Paul

    I also experienced the problem of the missing cpu with a Core 2 Duo Asus N90S notebook and Ubuntu 10.10. Also, the system would only boot the LiveCD and finished installation with "nolapic" in the kernel params. Under 9.10 the system behaved normally.

    Under 10.10, removing the NVidia driver did not fix the missing cpu for me and isn't the only problem.

    After reading some other cases of this I had a feeling a kernel compile was in order.

    I grabbed the official ubuntu linux kernel source module and compiled a new kernel, with the correct CPU type selected, Power Management disabled and CPU_HOTPLUG disabled. Installing that kernel brought back the second cpu, and ability to correctly boot up without the special "nolapic" setting.

    I'm posting this in the hopes it will be useful to other people having problems.


    • Related Question

    What do "processor" and "cpu cores" mean in /proc/cpuinfo?
  • why

    Possible Duplicate:
    Difference Between Cores and Processors

    What do "processor" and "cpu cores" mean here?

    cat /proc/cpuinfo 
    processor   : 0
    vendor_id   : GenuineIntel
    cpu family  : 6
    model       : 15
    model name  : Intel(R) Core(TM)2 Duo CPU     T5670  @ 1.80GHz
    stepping    : 13
    cpu MHz     : 1801.000
    cache size  : 2048 KB
    physical id : 0
    siblings    : 2
    core id     : 0
    cpu cores   : 2
    apicid      : 0
    initial apicid  : 0
    fdiv_bug    : no
    hlt_bug     : no
    f00f_bug    : no
    coma_bug    : no
    fpu     : yes
    fpu_exception   : yes
    cpuid level : 10
    wp      : yes
    flags       : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida dts
    bogomips    : 3591.62
    clflush size    : 64
    cache_alignment : 64
    address sizes   : 36 bits physical, 48 bits virtual
    power management:

    processor   : 1
    vendor_id   : GenuineIntel
    cpu family  : 6
    model       : 15
    model name  : Intel(R) Core(TM)2 Duo CPU     T5670  @ 1.80GHz
    stepping    : 13
    cpu MHz     : 800.000
    cache size  : 2048 KB
    physical id : 0
    siblings    : 2
    core id     : 1
    cpu cores   : 2
    apicid      : 1
    initial apicid  : 1
    fdiv_bug    : no
    hlt_bug     : no
    f00f_bug    : no
    coma_bug    : no
    fpu     : yes
    fpu_exception   : yes
    cpuid level : 10
    wp      : yes
    flags       : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida dts
    bogomips    : 3590.97
    clflush size    : 64
    cache_alignment : 64
    address sizes   : 36 bits physical, 48 bits virtual
    power management:

    • Related Answers
  • Pops

    In this case processor is just an identifier (which starts at 0). You have two processors, so they're 0 and 1. CPU cores means the number of cores in each physical processor (two here).

  • Matt

    It is two processor cores on one die essentially like having a dual processor system in one processor.

    The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions.