Re: CPU Utilization

[Anthony Liguori <aliguori@us.ibm.com>]

top isn't smart enough to realize that for a portion of the running 
time, a domain has been pre-empted out and is not running.

top will then charge whatever was running at pre-emption time for the 
time that other domain running.

Regards,

Anthony Liguori

Dave Thompson (davetho) wrote:

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>>-----Original Message-----
>>From: Rob Gardner [mailto:rob.gardner@hp.com] 
>>Sent: Monday, December 12, 2005 1:23 PM
>>To: Dave Thompson (davetho)
>>Cc: xen-devel@lists.xensource.com
>>Subject: Re: [Xen-devel] CPU Utilization
>>
>>Dave Thompson (davetho) wrote:
>>
>>    
>>
>>>I have a question concerning the CPU utilization number provided by
>>>the 'xm top' command in xen 3.0.  I've noticed that if I run a TCP
>>>performance tool on domain 0 which simply receives and echos back
>>>a TCP stream, the output of 'xm top' during the test does not match
>>>up with the output of 'top' on domain 0 in terms of CPU utilization
>>>(nor with the CPU utilization computed by the test program).
>>>
>>>...
>>>
>>>Any idea why these displays disagree?
>>> 
>>>
>>>      
>>>
>>Top shows cpu usage for user processes in dom0, while xm top 
>>shows cpu usage for the domain, which includes cpu time spent
>>in the dom0 kernel.
>>    
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>Doesn't top's CPU summary line show both?  I thought us=user space,
>sy=system, ni=nice, id=idle, hi=hwintr, si=softintr.  So in my
>example 1% in user space, 7.3% in system level, 3.3% in h/w intr,
>and 15% in soft intr.  Total of 26.6% utilized of which 25.6% is
>in kernel.
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>>Perhaps the thing you're running incurs lots of kernel cpu 
>>time, but not 
>>user time?
>>
>>Rob
>>
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