CentOS 6.x High CPU usage in power_saving threads

Posted: 2015-07-29 09:02:08 by Alasdair Keyes

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I was awoken at 3am this morning by a backup server complaining about high CPU... because these things never happen at a nice friendly time like 3pm Monday to Friday.

It looked that the kernel's power saving threads were using a lot of cpu on this CentOS 6.6 box.

# top

top - 08:40:21 up 84 days, 22:46,  1 user,  load average: 7.49, 7.51, 7.60
Tasks: 269 total,  14 running, 255 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us, 72.8%sy,  0.0%ni, 27.2%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  16249656k total,  2427188k used, 13822468k free,   185756k buffers
Swap:  4194300k total,        0k used,  4194300k free,  1523072k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                              
 2089 root      -2   0     0    0    0 R 100.0  0.0 359:08.11 power_saving/4                                                                                                                                      
 2086 root      -2   0     0    0    0 R 97.4  0.0 358:49.54 power_saving/1                                                                                                                                       
 2088 root      -2   0     0    0    0 R 97.4  0.0 358:55.72 power_saving/3                                                                                                                                       
 2085 root      -2   0     0    0    0 R 95.7  0.0 358:42.58 power_saving/0                                                                                                                                       
 2087 root      -2   0     0    0    0 R 95.7  0.0 359:00.27 power_saving/2                                                                                                                                       
 2090 root      -2   0     0    0    0 R 95.7  0.0 359:10.27 power_saving/5          

Stopping the acpid service didn't seem to help and the only thing that resolved the issue was to unload the acpi_pad module from the kernel. At which the power_saving threads were removed and the load dropped again.

# service acpid stop
Stopping acpi daemon:                                      [  OK  ]
# lsmod | grep acpi_pad
acpi_pad               87985  0 
# rmmod acpi_pad
# lsmod | grep acpi_pad
#

There is a Redhat advisory of a similar issue, but this indicates that it's only on CentOS 6.2, but it appears that it has continued into later revisions of the Redhat kernel.

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