I've been dealing with issues with my Windows 11 VM forever and I can't seem to figure out what the issue is. It gets very sluggish, jittery and choppy. It acts as if it just doesn't have enough resources but it does. It's not all the time either. It really only happens when it needs more resources, like I open a program. But it has plenty of resources and I've check the RAM and CPU usage and it looks normal. What I mean by that is it has nominal spikes for the RAM and CPU, as you would expect when opening a new program, yet it behaves as if the CPU and/or RAM is maxed out. After a bit, it smooths out and is fine.

I recently found a possible clue when playing Fortnite. It is virtually unplayable normally, but it's ok if I enable the "Performance mode" in Fortnite. It will be a bit sluggish at first but if I wait for a bit, it starts working fine. Sometimes it takes minutes. Sometimes it will start to slow down in the middle of a game, but after a while, it will start to work. It's like night and day, because it will be a few frames a second, choppy video and audio, and then it seems like it "catches up" and it's instantly super smooth. It may be unrelated, but when I check the performance metrics in the Windows task manager it only seems to happen when the SSD drive utilization is over 7%.

Here are my specs:

VM:
24 cores, 32GB RAM (also tried a VM with 8 cores and 8GB RAM)

CPU pinning, huge pages enabled (sysconfig: append transparent_hugepage=never default_hugepagesz=1G hugepagesz=1G hugepages=64 isolcpus=12-31,44-63)

Hardware:

Motherboard:	Gigabyte Technology Co., Ltd. TRX40 DESIGNARE
BIOS:	American Megatrends International, LLC. Version F7f Dated 09/24/2025
CPU:	AMD Ryzen Threadripper 3970X 32-Core @ 3700 MHz
HVM:	Enabled
IOMMU:	Enabled
Cache:	L1 - Cache: 2 MiB, L2 - Cache: 16 MiB, L3 - Cache: 128 MiB
SSD	Rocket 2TB (two slightly different models)
GPU	Nvidia RTX 4070 (passed through, latest driver)
Memory:	128 GiB DDR4 Multi-bit ECC (4x 32GB Kingstom 9965745-020.A00G)

I've tried everything I can think of:

• CPUs pinned (in pairs)

• Enabled hugepages

• Only one numa node

• Reinstalled windows on different VM

• GPU passthrough

• SSD controller passthrough

• Updated UEFI

• Disabled virtual memory/page file in Windows

• memtest86+

• Windows Power Plan: High Performance.

• Core Isolation / Memory Integrity: OFF.

• BitLocker: OFF / Fully Decrypted.

• Write Caching: Enabled in Device Manager

• Global C-States: Disabled

• IOMMU / SVM: Enabled

I'm sure there are other things I have tried that I am forgetting and I will try to keep the list updated. I've seriously been trying to figure this out for at least a year. I'm pretty sure I've updated my GPU firmware but I might check that again. I'm wondering if it might be because my RAM is meant for servers and not gaming. But that seems a little far fetched. I might try disabling ECC, but it's hard to find a good time to reboot the server and test that. Short of wasting a bunch of time researching and disabling or enabled UEFI settings, I'm pretty much out of ideas.

Edited November 26, 2025Nov 26 by bobbintb

Just for anyone else that might be having a similar issue, I am fairly certain I found the cause. I have a riser cable for my GPU and I believe that is the culprit. I found that out by running this command:
lspci -vv -s 21:00 | grep -E "LnkCap|LnkSta"

The 21:00 part is the bus address of my GPU, which can be found under Tools>System Devices in the Unraid UI. This is the output I got:

                LnkCap: Port #0, Speed 16GT/s, Width x16, ASPM L1, Exit Latency L1 <4us
                LnkSta: Speed 2.5GT/s (downgraded), Width x16
                LnkCap2: Supported Link Speeds: 2.5-16GT/s, Crosslink- Retimer+ 2Retimers+ DRS-
                LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete+ EqualizationPhase1+
                LnkCap: Port #0, Speed 16GT/s, Width x16, ASPM L1, Exit Latency L1 <4us
                LnkSta: Speed 2.5GT/s (downgraded), Width x16
                LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete- EqualizationPhase1-

You can see the speed has been downgraded to 2.5GT/s, which is PCIe 1.0 speed, not PCIe 4.0. I haven't yet taken the time to install my GPU directly into the slot because I have to do a lot of reconfiguring, but I am fairly certain that is evidence enough that that is the issue.