Ubuntu: CPU is maxing one core and not using others (John The Ripper)


I just built a new computer last week and have been running Ubuntu 14.04. I've noticed it only ever runs one core hard and the others will be below 5%. I was running John The Ripper just now and it would only max one CPU. I tried changing the affinity...

andrew@andrew-MS-7817:~$ taskset -p 0xFFFFFFFF 14219  pid 14219's current affinity mask: 3  pid 14219's new affinity mask: f  

Nothing changed on the system monitor though... 3 of the CPU's were still under 5%. I also did a lscpu and this was the output...

andrew@andrew-MS-7817:~$ lscpu  Architecture:          x86_64  CPU op-mode(s):        32-bit, 64-bit  Byte Order:            Little Endian  CPU(s):                4  On-line CPU(s) list:   0-3  Thread(s) per core:    1  Core(s) per socket:    4  Socket(s):             1  NUMA node(s):          1  Vendor ID:             GenuineIntel  CPU family:            6  Model:                 60  Stepping:              3  CPU MHz:               3614.402  BogoMIPS:              6599.82  Virtualization:        VT-x  L1d cache:             32K  L1i cache:             32K  L2 cache:              256K  L3 cache:              6144K  NUMA node0 CPU(s):     0-3  

I've never noticed the CPU go above 30% usage... Any ideas?


This is because the application that is using the CPU (john in your case, but mysqld does the same when running a single query) is monothread, so it can use only one core at a time. An application that support multithreading will be able to use more than one core at the same time.

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