@redakula said in CPU C-states:

@FrankAtHome
I looked in to this as well a while back and the conclusion i came to, is that the newer AMD power management functions are not supported properly in the old kernel used by XCP-NG (And maybe xen?).
A lot of work seems to have been done in the 6.x kernel series on this.

I get the same on my 7900 - only C0 and C1
I tried booting it on a Ubuntu 24.04 live cd and power consumption was easily 15% lower at idle.

that sounds plausible as explanation.

I guess I will have to patiently await XCP-ng 6 branch and any improvements this may bring on AMD systems.

@Andrew

ok that's interesting.

Which CPU is this on? AMD ? Intel ?
Did you specify any boot parameters in grub to unlock these C-States ?

Hello,

One of the homelab platforms I'm running XCP-ng on, is a AMD 7950X.
I recently noticed, that in Ubuntu Linux 24.04, PowerTop reports C-states C1-C3 (see screenshot).

However, in XCP-ng 8.3, the command « xenpm get-cpuidle-states » only reports C0 and C1.

I've tried adding « cpuidle » to the Xen image boot parameters in Grub-efi.cfg which doesn't seem to make any difference to the output of the get-cpuidle-states command. Looking at the output of « xe host-dmesg » I am not sure what to look for; the lines referenced in an Xen documentation page do not seem to be present in the output on XCP-ng.

As this is a homelab project, I wish to reduce power consumption as much as is technically feasible and leverage the supported C-states (unless latency from switching to/out of C3 would be killing performance).

@633kD4d
Same issue here trying to pass through a UPS usb device to a Linux guest.

VM won't start with VUSB active and the same error about fail to reset.