High system cpu load (%sys), system locks

Posted by Mark on Server Fault See other posts from Server Fault or by Mark
Published on 2011-11-03T16:38:26Z Indexed on 2012/11/30 23:07 UTC
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linux

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cpu

For the last two weeks we are having intermittent severe spikes in system cpu usage (shown as %sys), which last for maybe half a minute, locking most processes, including ssh.

I've been trying to figure this out, but atop doesn't show anything relevant (system usage for processes it shows is insignificant), spikes are intermittent and I could not reproduce the spike using any workload for the web application this webserver hosts.

If you have any ideas on how to debug high %sys and (sometimes) %si CPU usage, please share them.

System specs (don't know if any of this is relevant): Dedicated server, CentOS 6, core i7 950, consistent 4 to 8 GB RAM free at any time, hard drives are in RAID-1.

Additional info:

dmesg output doesn't change between spikes
/var/log/messages doesn't change between spikes
Here is cat /proc/vmstat
Here is output of mpstat 1 during a typical spike

Add 07.11.11: looks like simple reboot restored system state, and we might never know what caused the disturbance in first place.

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