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Can a Hyper-V VM CPU be optimized

Posted on 2016-09-30
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Last Modified: 2016-10-02
One of our heavy usage VM's at times has the CPU jump to 85 %.   It has 4 Virtual Processors.   Are there any tricks to get better CPU performance?
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Question by:jrsitman
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Expert Comment

by:Jack Rider
ID: 41824364
Why not just increase the number of vCPUs?
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Expert Comment

by:Adam Brown
ID: 41824373
1. Make sure the Host is not configured to use Hyper-threading. Hyper-V's CPU management system requires the use of physical cores to run properly.
2. Make sure the VMs on the host are not configured to utilize more CPUs than are available. CPU double booking on the host can cause random excess utilization. This is part of why you don't want to use hyper-threading, since it can end up with multiple instances of VMs trying to use the same physical CPU.

Aside from those things, you're mostly going to be dealing with the OS on the VM, which would require a good bit more planning and examination to really handle. That said, though, 85% isn't a bad utilization level for short periods. At that level, you're not seeing a CPU bottleneck for performance, so I wouldn't worry *too* much about it. But you'll want to spend some time examining which processes use the most CPU, particularly during CPU spikes. If stuff related to the application the server is running are the only things spiking CPU utilization. Also use process explorer when you do this, since it will give you a better view of memory usage.

In the end, though, tracking down potential performance sinks is a very involved process that can take a long time to be successful at. Unless your hardware is completely pegged for long periods and users are complaining about slowness, you're usually better off letting things go as they are than you are tracking down bottlenecks and re-designing the infrastructure.
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by:jrsitman
ID: 41824376
Thanks.  Do you see anything I need to be concerned about?

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Lee W, MVP earned 500 total points
ID: 41824509
REDUCE the number of CPUs.  Unless you have a LOT of cores, you don't want to assign that many if at all possible.  See http://www.zdnet.com/article/virtual-cpus-the-overprovisioning-penalty-of-vcpu-to-pcpu-ratios/
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by:jrsitman
ID: 41825009
How many should there be?
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Assisted Solution

by:Lee W, MVP
Lee W, MVP earned 500 total points
ID: 41825072
Read the article - I start with 2 so I have one in case a process goes nuts and hogs one.  But if your machine has 4 cores and you assign all 4 to the VM, it's going to have performance issues compared to 2 to the VM.  If you server has 16, then it's probably ok with 4, but EVEN SO, I would START with two and only add as I determined it was needed - and then only one at a time.
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by:jrsitman
ID: 41825429
thanks
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