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View Full Version : [ubuntu] 12.04 suddenly lost 3 cores



potatochip
July 16th, 2012, 03:12 PM
I have a 12.04 system with a quad core CPU.
I noticed today though only one CPU is now being used.
Nothing has changed on the box except an apt-get upgrade and it has been happily running it's 4 cores for 4 or 5 years.
I'm out of the country so I haven't been fiddling with the BIOS and unfortunately can't check any of the BIOS settings either.

Has anyone else had this happen?

Here's the output of cat /proc/cpuinfo showing just the one entry rather than the usual four. htop and top also show just the single core.

processor : 0
vendor_id : AuthenticAMD
cpu family : 16
model : 5
model name : AMD Athlon(tm) II X4 620 Processor
stepping : 2
microcode : 0x1000086
cpu MHz : 800.000
cache size : 512 KB
physical id : 0
siblings : 1
core id : 0
cpu cores : 1
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 5
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt npt lbrv svm_lock nrip_save
bogomips : 5224.07
TLB size : 1024 4K pages
clflush size : 64
cache_alignment : 64
address sizes : 48 bits physical, 48 bits virtual
power management: ts ttp tm stc 100mhzsteps hwpstate


Here's my uname -a
Linux twistie 3.2.0-25-generic #40-Ubuntu SMP Wed May 23 20:30:51 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

in case it's useful.

sanderj
July 16th, 2012, 04:43 PM
You could use these commands:


$ grep -i cpu /var/log/syslog | grep -i "is up"

Jul 16 11:34:43 R540 kernel: [59481.560009] CPU1 is up
Jul 16 11:34:43 R540 kernel: [59481.591844] CPU2 is up
Jul 16 11:34:43 R540 kernel: [59481.623894] CPU3 is up

(which is the output for my 2-core 2-thread-per-core CPU)


And:


$ grep -i cpu /var/log/syslog


And have you tried a reboot?

potatochip
July 16th, 2012, 07:01 PM
That would just show what I already know; that the cores are not up.
I've tried a reboot too. I also commented out the latest kernel lines from menu.lst so I was using an old kernel that I knew saw all four cores but this didn't work either.
My best guess is my bios has somehow reset itself with acpi disabled.

sanderj
July 16th, 2012, 07:13 PM
That would just show what I already know; that the cores are not up.
I've tried a reboot too. I also commented out the latest kernel lines from menu.lst so I was using an old kernel that I knew saw all four cores but this didn't work either.


Aha. So you had already had done the things I adviced, but you didn't tell that in your first post?

potatochip
July 16th, 2012, 07:57 PM
My bad. I'd assume rebooting is the first thing most people try when something that should work doesn't.
Is it even possible for a bios to reset options with no manual l intervention? Or is it possible that an upset has caused this?
Without physical access to the box I can't check the bios but looking at the grub files it seems nothing has changed with how it boots for a while.
Does anyone have any idea what I should be looking at to debug this?

sanderj
July 16th, 2012, 08:11 PM
Dmidecode to check what BIOS says?

EDIT:

This is my output:


$ sudo dmidecode | grep -i core
Family: Core i7
Core Count: 2
Core Enabled: 2
$

Or


sander@R540:~$ sudo dmidecode -t processor | tail -10
L3 Cache Handle: 0x0007
Serial Number: Not Specified
Asset Tag: Not Specified
Part Number: Not Specified
Core Count: 2
Core Enabled: 2
Thread Count: 4
Characteristics:
64-bit capable

sander@R540:~$

potatochip
July 18th, 2012, 08:08 PM
Bizarre. I've finally got back to my machine so I could take a look around the BIOS. There were no APIC options which a few other posts had pointed me in the direction of so I exited without saving.
Now I can see all four cores again.

I'm confused as to what's been going on but at least everything is back as it should be. Has anyone seen anything like this before?

JackRabid
July 18th, 2012, 08:47 PM
A similar problem is why I'm here- I have an older IBM server with 2 dual-core Xeons and the system suddenly starts showing 2 cores when it used to say 4. Difference is that I'm still running 10.04.

Initially I thought it was heat related and had powered the machine down. I guess I need to head over to it's physical location so I can get it booted and poke at the BIOS.

I love linux and what I'm learning with it, but issues like this can make it very difficult to have faith in a one's abilities when considering greater and more challenging endeavors.

:edit: Got a chance to sit down at the console and poke at the BIOS a bit. Noticed that HyperThreading was disabled so I enabled it 'save and edit'ed, rebooted and checked top. Still showing 2 'processors'. Did some googling. Had dinner. Drove back. After 20 minutes of looking at random bios categories multiple times I noticed that HyperThreading was again showing as disabled. So I again Enabled. Then I saved. Then I again 'save and exit'ed. This time when I checked top it was finally showing me 4 'processors' again.

I wonder how HyperThreading got disabled to start with. Curious that I had to enable HyperThreading twice... ...any how, it works. I'll take it. :/edit: