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Very high CPU on virtual server (VMWare guest) - same application on physical server has no problem

Posted on 2013-05-15
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Last Modified: 2013-07-06
We run a video recording/archiving application called Digital Sentry.  Currently we have several physical Windows 2008 R2 servers each recording video from 30 to 60 cameras.  There is not special hardware installed...data is pulled from cameras over TCP/IP and written to iSCSI volumes.  Each physical server has 4 cores (2 dual-core sockets) and 8GB memory.  CPU usage is usually very low (about 10%) and memory usage is also low.

But when we try running this application on a virtual server (VMWare ESX 5), even a small number of cameras (4) quickly pushes CPU above 50%.  This makes no sense.

Any ideas?
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Question by:Carlo-Giuliani
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by:Nagendra Pratap Singh
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What is the VM version?

Are you using E1000 NICs or VMware paravirtualised ones?

iscsi is used on both physical and virtual servers?

VMware tools are installed?

How many VCPus are you using in the virtual machine?

Is your esx/esxi more powerful than the original server?
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by:piyushranusri
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what graphic memory is configured on physical and Virtual.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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1. Check the VM has no Snapshot.

2. How many vCPUs have you added? More than 2?

3. What is the underlying datastore fabric? RAID 1, 10, 5

4. What are the hosts disks? SATA or SAS

5. How many disks?

6. Speed of disks?
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by:Carlo-Giuliani
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No snapshot, 2 vCPUs, VMFS datastore on NFS volume on NetApp aggregate of 24 SAS (15Krpm) disks.  The VM virtual hardsware version is 8.  The network driver is VMXNET3 and the VM is using the paravirtual SCSI driver (so, of course, VM tools is installed).

We are NOT beginners at VMWare.  We run about 150VMs on the same cluster.  This is the only one that behaves like this.
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by:Andrew Hancock (VMware vExpert / EE MVE)
Andrew Hancock (VMware vExpert / EE MVE) earned 250 total points
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In that case, seen issues like this before with realtime applications, VM under a Hypervisors performs poorly compared to the physical server.

I assume you are using Jumbo Frames for NFS access.
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asavener earned 250 total points
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The CPU % in performance monitor is an unreliable measure on a virtual machine.  The hypervisor only offers CPU if the guest asks for it, which means that CPU % looks high even when the hypervisor still has plenty of capacity.

A better measure is CPU_Ready.  This measures how often the guest is asking for CPU cycles, and the hypervisor is making it wait.

Remember that all vCPUs for a guest have to be scheduled simultaneously, so CPU_Ready is typically higher for guests with multiple vCPUs.

Sometimes you can get better performance by reducing the number of vCPUs (because the performance bottleneck is scheduling, rather than CPU cycles).  Only use the number of vCPUs that you actually need.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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Do you need further help with this question?
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by:Carlo-Giuliani
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I've requested that this question be deleted for the following reason:

None of the responses were helpful.  I was looking for reasons why software running on a VM might use much more CPU than the same software running on physical hardware.  General advice on tuning VMware or vague statements like "hypervisors perform poorly compared to physical" are no help.
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by:Nagendra Pratap Singh
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If you host is not feeling any load then let the VM monitors show any amount of cpu load. Are you getting slow images transfer etc?

If you want exact help then you need to get someone in your office and BTW even beginners run 150 VMs. It is so easy!
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by:asavener
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The CPU % in performance monitor is an unreliable measure on a virtual machine.  The hypervisor only offers CPU if the guest asks for it, which means that CPU % looks high even when the hypervisor still has plenty of capacity.
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by:asavener
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I meant that last post as an objection....

We did answer why CPU usage will appear high in a VM.  You have to go look at other metrics to determine if the CPU usage is actually greater, such as the performance tab for the VM.
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by:Carlo-Giuliani
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I've requested that this question be deleted for the following reason:

Bottom line is I got nothing usefull, so I don't want to award points.  
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by:asavener
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"Nothing useful?"  That seems a little hyperbolic.

Perhaps the answer was not answered to your satisfaction, but we attempted to assist and you provided minimal feedback.
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by:Andrew Hancock (VMware vExpert / EE MVE)
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I asked you a question in http:#a39199703

Do you need further help with this question?

you did not respond, other than to delete the question!
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by:Carlo-Giuliani
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I've requested that this question be deleted for the following reason:

, I've decided this is not a good use of my time  Nobody seems to have any experience of specify application behavior that leads to unreasonably high CPU usage on a virtual machine.
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by:asavener
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Question:  
But when we try running this application on a virtual server (VMWare ESX 5), even a small number of cameras (4) quickly pushes CPU above 50%.  This makes no sense.

Any ideas?

Answer:
The CPU % in performance monitor is an unreliable measure on a virtual machine.  The hypervisor only offers CPU if the guest asks for it, which means that CPU % looks high even when the hypervisor still has plenty of capacity.

Simply changing the text of your delete request does not make the delete request valid.
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by:asavener
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My recommendation is to delete with no refund.

If that is not an option, then I would recommend splitting points among all participating experts.
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