Performance penalty of CPU limited algorithms in a VM

[WaitingForNehalem]

I am a graduate student in Computer Science and use Linux for development. Some of the algorithms I write take a long time to complete, especially if they aren't vectorized. Using x86 virtualization extensions, I read that the performance penalty of running in the guest vs the host is nearly gone since it essentially time slices the CPU. However, I've heard of problems where number crunching or compiling in a VM is really slow. Also I'm not using a bare metal type 1 hypervisor, just VMWare Player running on Windows 10. Does anyone have any experience with CPU intensive work running in a VM?

 

[ninaholic37]

This function took like 100x longer in VMWare than natively last time I tried it

https://github.com/Fleex255/TED5/blob/master/JHUFF.C#L948

 

[Hajime]

If you are using a type 2 hypervisor like VMWare Player, it is going to be incredibly slow in the circumstances you describe under certain conditions no question.

A type 1 hypervisor with modern hardware can see a peformance penalty in the single digits, but a type 2 can wreck havoc with performance (Based on testing at work, double digit penalties or more) under the same operations.

However, you are using Windows 10. The client Hyper-V in Windows 10 is type 1, and Windows 10 does have a full version of it. Why are you using VMWare Player over Hyper-V?

 

[WaitingForNehalem]

I actually didn't know it was type 1. I've tried using Hyper-V but graphics support is quite poor. Modern distros need some type of 3D acceleration for the UI. CentOS 7 for example runs terribly in it and while I do mostly use the terminal, I still need a GUI for looking at image outputs. I guess Ubuntu MATE or a GNOME 2 distro would do better. So it looks like using a type 2 is out of the question.

 

[zir_blazer]

"VM" and "3D acceleration" in the same Thread? This is for you.

The three big points:
CPU performance wasn't heavily penalyzed, it should be around 10% overhead or so.
GPU is non-existent unless you do VGA Passthrough, otherwise you have either a very basic emulated VGA, or one that does API forwaring for mediocre DX9/OpenGL support but lacks performance.
I/O sucks if you're using file backed storage for VMs. Its performance is decent if you're dealing with big files, but goes to the toilet if you're working with tons of small files. You may want to use a logical volume solution like LVM, but you VMM needs to support doing so, and you need to partition the HD accordingly before using.

 

[Fox5]

Virtual machines have poor i/o performance (especially for graphics), and high memory overhead.
User mode cpu performance is nearly untouched though.

 

[WaitingForNehalem]

Well I decided to just dual boot. Not sure I even need the Windows partition honestly.