Adding more than 2 cores (and the HT pairs) to my Windows 10 VM causes major stuttering.


nlash

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Using a Ryzen 2700x.

 

I've tried various groupings of cores (always along with the grouped HT pair) and anything over two cores causes the entire vm (mouse included) to massively stutter every couple of seconds.

 

I've tried everything under the sun and this is the only way I can get a stutter-free Windows 10 VM.

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I saw something like this today.  I tried it many times with little tweaks to the configs because I didn't believe what I was seeing, but you are right this is a thing!

 

I have a Ryzen 7 3800X on a ASUS ROG Strix x570-E board with bios 1405 AGESA 1.0.0.4 Patch B, and I saw significant input lag/stutter (i.e. mouse cursor skipping) when isolating CPUs from different CCXs.  I didn't even have to use them in the VM ... just isolating CPU cores in Unraid from different CCXs and starting the VM using cores for 1 CCX (or both) was enough to cause the lag.

 

Here is my CPU architecture which is similar to yours.  I passed the 2nd CCX (cores 4-7 & 12-15) and a HT core from the 1st CCX (cores 3 & 11) leaving the rest of the 1st CCX for Unraid during my testing.

 

topo_cogsworth_v3.thumb.png.7268d4e89a44487331364ee77b626432.png

 

This may be more complicated of an issue for me as I am having other VM stuttering issues which I posted about here. 


But I wanted to validate your finding!  You're not crazy!  

 

-JesterEE

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It's good to know I'm not crazy. 

 

Just to add another data point...I currently have cores 3, 5, and 7 isolated for my Windows VM. If I'm reading my architecture correctly, that's across two CCXs.

 

It runs perfect.

 

If I add another core—any core—guaranteed stuttering. My emulator is on core 0.

 

Luckily this is only a gaming VM, so three cores is enough, but I've never been able to solve it.

 

My MacOS VM that uses those cores plus core 1 runs like butter.

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  • 1 year later...

Very interesting!

I have exactly the same problem.

I could not add more than 2 cores before the stuttering began in Windows, but I did not test the 3,5,7 combo, which actually works, so now I have 3 working cores, so thank you for that.

Also, MacOS runs as butter with more cores for me as well.

Any new findings in this matter, as the last post is over a year old?

Edited by joggs
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On 1/8/2021 at 10:50 AM, joggs said:

Very interesting!

I have exactly the same problem.

I could not add more than 2 cores before the stuttering began in Windows, but I did not test the 3,5,7 combo, which actually works, so now I have 3 working cores, so thank you for that.

Also, MacOS runs as butter with more cores for me as well.

Any new findings in this matter, as the last post is over a year old?

 

 

I've actually since upgraded to a 3900x. 

 

But, before the upgrade the problem went away and I was able to add 4 cores. I don't know what updated or what changed, but something fixed it. 

 

I currently have 8 cores passed to both VMs (not simultaneously) and everything runs fine. 

 

No clue what changed. 

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