Protip: If your Host is PCI-E 2.0 but your Guest is seeing PCI-E 3.0, turn off ASPM

Hardware GPU
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I was wondering why my GTX 1080 was having performance issues in my Kubuntu 18.04 VM with Unigine Superposition, but worked fine with everything else including Unigine Valley… Then it dawned on me… My Host system is PCIE 2.0 and the VM is seeing 3.0… 3.0 introduced ASPM and that could affect how the card reacts if there’s version differences between the host and the VM.

Before the fix, I was only getting 19fps in 1080p Medium Superposition. After the fix, with 3 hyperthreaded cores, 110fps.

The fix? This simple kernel parameter: pcie_aspm=off

At least that’s how to fix it for a Linux guest, but I wonder if there’s a KVM kernel argument to globally apply that for all VMs upon host boot? Windows has no ASPM management,

This should help those on X58 or X79.

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Nice find :+1:

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There was talk of a wiki in anther thread this would def be a candidate entry

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Yes, a global ASPM off switch for all KVM/QEMU VMs as a kernel argument would be very nice for those of us running PCI-E 2.0 host systems.

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