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2918 Views 5 Replies Latest reply: Jun 25, 2012 8:44 AM by thedada RSS
thedada Rank: White Belt
thedada
14 posts since
May 16, 2012
Currently Being Moderated

May 16, 2012 8:16 AM

Weird Results with Virtualized CPU monitoring

Hi there !!

 

I just started with some tests with zenoss.

My VM's test run on KVM Hyperviseur  related to a Cloudstack Server.

 

I settle up a simple snmp monitoring for basics check first .

All was good and the graph looked nice but when I tried stressing the cpu (with a stress --cpu 10 --timout 30 for example) and watching locally my CPU % Use (100% for the stressed time) I can only see some 20-30 % use on the zenoss graphs.

 

I tried stressing more but on the graph, it never reached the 100%.

 

I tried to figoured out how this monitoring works, and it's just some simple snmp trap ( I dident tried with a SSH monitoring yet )

 

Did someone already have the same results ?

 

 

Ty for your time.

 

Cheers.

  • Rank: Green Belt
    Daniel Robbins
    70 posts since
    Jan 24, 2012
    Currently Being Moderated
    1. May 30, 2012 12:47 AM (in response to thedada)
    Re: Weird Results with Virtualized CPU monitoring

    For each measurement, are you measuring within the (K)VM or on the host? Can you post the specific commands you are using to determine CPU usage?


    Thanks

  • thedada Rank: White Belt
    thedada
    14 posts since
    May 16, 2012
    Currently Being Moderated
    2. Jun 4, 2012 4:05 AM (in response to Daniel Robbins)
    Re: Weird Results with Virtualized CPU monitoring

    hi Daniel,

     

    Thank you for your answer.

     

    I'm directly on the host using a simple top command.

    With a physical computer, the graph and the top command results are the same.

     

     

    I'm gonna have a look at the cloudstack plugin to see if I can monitore host trough that and if the results are more accurate.

     

    Cheers

  • Rank: Green Belt
    Daniel Robbins
    70 posts since
    Jan 24, 2012
    Currently Being Moderated
    3. Jun 4, 2012 12:50 PM (in response to thedada)
    Re: Weird Results with Virtualized CPU monitoring

    If you are looking at "top" on the host, then the CPU may in fact be saturated inside the VM. The VM may only have one of your cores and that would explain why it cannot saturate the host's CPU -- it only has "a piece" of it.

     

    Be sure to compare "top" inside the VM and on the host, and also compare "cat /proc/cpuinfo | grep -c ^processor" on the host and inside the VM. This will show you how many cores are inside the VM vs. the host.

     

    The CloudStack ZenPack should make this a bit more clear, I think.

  • thedada Rank: White Belt
    thedada
    14 posts since
    May 16, 2012
    Currently Being Moderated
    4. Jun 19, 2012 5:30 AM (in response to Daniel Robbins)
    Re: Weird Results with Virtualized CPU monitoring

    Hi Again !!!

     

    Well I tried some other things to understand how zenoss really monitor the CPU usage.

    So my host is a 24 core server.

    I took 2 VMs :

     

    One is monitored by snmp.

    Other one is monitored via ssh.

     

    I go on the VM, I stress it such as :

    stress --cpu 30 --timeout 60

     

    and with a top on the VM, I get a 100% CPU usage . When I look at /proc/stat, I only see numbers raising.

    I tried a bash script that use /proc/stat to get the CPU Usage  http://colby.id.au/node/39 and it return 100%.

     

    And when I look on my zenoss Graph CPU Usage, I only get around 20 % In Both cases.

     

    I tried to figered out how zenoss buidl those graphs and get those results but can't find it ...

     

    I also tried libvirt zenpack but impossible to make it works.

  • thedada Rank: White Belt
    thedada
    14 posts since
    May 16, 2012
    Currently Being Moderated
    5. Jun 25, 2012 8:44 AM (in response to thedada)
    Re: Weird Results with Virtualized CPU monitoring

    I keep going further with this.

    At the end, when I try a ssCPUiddle on a server on which I'm stressing the CPU, i get the good result via SNMP .I only have something like 3 sec difference. On the graph , if I stress it for a long time , I get the good result. But if stress only for 60 seconds for example, I won't reach the 100% . So it seems to be the delay  between the incident and the graph's building that was bringing the wrong results for snmp.

     

    For ssh, when i run manually a cat /proc/stat I get some totally different results compare to the /sbin/cat /proc/stat launched via zenoss through ssh on the remote host. Can't understand why so far.

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