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Vdisk Activity Spikes CPU Usage

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Hello,

 

I've been working on optimizing my unraid server as I am now using a VM inside of it as my primary machine.  I've observed some behavior while testing and setting up that confuses me.  I've run VMs on here previously and gamed on them but more as a hobby rather than as my daily driver. 

 

If I set the emulatorpin to cores 1,13 (12 core xeon, so this is the 2nd core) and simulate a load (the one that causes problems reliably is the 2nd test on crystaldiskmark (the 8QD 8T test) and the emulator pin core maxes out to 100% and the VM stutters heavily.  Mouse movement is interrupted, videos stop, audio stutters.  Removing the emulatorpin setting and running nothing on the rest of the server shows unraid using 2-4 threads on unassigned cores near 100% utilization to provide the disk access to the VM which is running on isolated cores.  The VM cores also nearly max out during this time.  During this time the VM still has audio clipping issues but it is noticeably less of an issue.  With the q35 machine only 1 core maxed out on the VM, but multiple unassigned cores were still heavily used and the stuttering audio and mouse were still observed.

 

Is there a cpu cost to running vdisks/emulated block devices that I'm unaware of?  I've tried this with the disks set to virtio and sata, machine types set to 440 and q35, and with caching on, off, and set to directsync.  It didn't matter if the vdisk was hosted on my cache disk (960 evo pool) or a direct pass of the 860 evo ssd that I bought to try and alleviate this issue.  The only thing that resolved the machine response issues  was passing the nvme OS disk through to the vm directly and using it but that isn't ideal at this point in time.

 

If this is expected behavior that's fine.  Its just that I've seen people suggest the emulatorpin settings and I've seen them reply that it helped or did not help, but I have not seen anyone report that setting the emulator pin was so actively detrimental to the performance of their VM.  With the emulatorpin set to 1 or 2 threads even something like loading a game spikes the emulatorpin and the VM lags heavily.  I've experienced this trying to remove the occasional audio stutter in discord from my system.  

 

I'd appreciate any suggestions or ideas.  Thanks.

 

Edited by Iciclebar

Need Diagnostics file...

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