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Here is an example from my top:

Cpu(s):  6.0%us,  3.0%sy,  0.0%ni, 78.7%id,  0.0%wa,  0.0%hi,  0.3%si, 12.0%st

I am trying to figure out the significance of the %st field. I read that it means steal cpu and it represents time spent by the hypervisor, but I want to know what that actually means to me.

Does it mean I may be on a busy physical server and someone else is using too much CPU on the server and they are taking from my VM?

If I am using EBS could it be related to handling EBS I/O at the hypervisor level?

Is it related to things running on my VM or is it completely unaffected by me?

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3 Answers 3

up vote 9 down vote accepted

The Steal percentage (documented in the mpstat man-page) is indeed the hypervisor telling your VM that it can't have CPU resources the VM would otherwise use. This percentage is regulated in part by Amazon's CPU limiting, and VM load on that specific host. I/O load is monitored through the %io stat.

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ahh ... I was looking in the top man-page. So it could indeed be because I am on a machine that is getting used heavily by another user. On one of my EC2 instances I have seen it get as high as 65% –  Ben Feb 3 '11 at 16:59
    
@Ben Yeah, the fact that the info isn't in the top man page makes this harder than it needs to be. The stuff I've seen online suggests that certain EC2 machine types can peak as high as 70%. –  sysadmin1138 Feb 3 '11 at 17:50

Steal load accounts for time when your VM wanted to run something, but the hypervisor chose to run something else instead.

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man sar's

Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servicing another virtual processor.

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