Emulated CPU Performance

[Marshalleq]

The benefit of now having so many cores available to many of us means that we can dedicate some to a gaming VM.  However, for everything else, one option is to share the cores among the remaining apps.  That's exactly what I'm doing as I don't need 100% performance with super low latency on my other applications.  

 

So, to that end, does anyone know if there are any optimisation tricks for running a Linux VM under an emulated CPU environment?  I'm currently doing an encode this way and I would have expected it to be a bit quicker when I compare it to how it performs native on another machine.  I'm using Q35 3.1 which I'm about to dive into understanding.

 

Yes I appreciate I haven't given all information, that's intentional at this stage.

 

Thanks.

Edited May 26, 2019 by Marshalleq
Gramatical.

[John_M]

You probably need to read up on what features the QEMU emulated processor offers. It will be some subset of your Threadripper's native capabilities so, yes, I wouldn't be surprised to find it less capable at (video) encoding.

[Marshalleq]

Yes exactly, which is why I'm asking for if anyone knows of any optimisations.  I guess it's the downside of Unraid really, others such as Proxmox and so forth are quite optimised for VM's running under shared resources, as you'd expect.  The great thing about Unraid is it can still be done, with a few optimisations.  So, if anyone knows of any for emulated CPU setups, if you could post them here or point me at them (haven't found them myself yet).

 

Thanks.

[John_M]

I just use the real cores now that I have them. I only used the emulated ones when I was using low core count processors and never expected bare metal-like performance. So my "optimisation" was to switch to using real cores. I don't see any downside to doing that - they're still available for other uses when the VM in question isn't running. I'm not sure what you're trying to achieve as you say you've deliberately not told the whole story but you could try comparing the output of cat /proc/cpuinfo for the real and emulated cores to see what's missing from the latter.

 

According to CPU-Z running on a Windows 7 VM my system is emulating an AMD K6 but with 64-bit instructions. As common denominators go that seems fairly low and I don't think there's anything that can be done to optimise for it as the real cores are much more capable: