Public bug reported: After setting up a fresh VM on a Hyper-V host with the official amd64 Xubuntu Minimal 26.04 iso, I noticed unexpectedly choppy graphical performance when connecting to the guest console through VMConnect (Basic session). When dragging a window around the desktop, there was easily hundreds of milliseconds of delay or more between moving the mouse and the window actually moving.
I used xev to confirm this was a problem with the display and not the input (input events came in at a smooth rate). I investigated various Xfce and Xorg settings to no avail, then tried temporarily replacing Xfce with openbox, which exhibited the same choppiness. At this point, I went looking for differences with another NixOS VM on the same host which did not exhibit the problem and the only significant difference appeared to be that it was running a 6.18 kernel instead of 7.0.0-30-generic like Xubuntu. I installed a 6.18.43 kernel on Xubuntu and the problem disappeared, obtaining performance comparable to the NixOS VM. I had ChatGPT 5.6 do some research and it suggested the problem might be the following commit: 52e6b19 drm/hypervdrm: Use vblank timer It noted that this commit was reverted by Red Hat in one of their kernel branches in June 2026 according to the changelog at rpmfind.net/linux/RPM/centos-stream/9/baseos/x86_64/kernel- tools-5.14.0-719.el9.x86_64.html. To test this hypothesis, I cloned the kernel sources from https://git.launchpad.net/~ubuntu- kernel/ubuntu/+source/linux/+git/resolute, switched to tag Ubuntu-7.0.0-30.30 (d974a40), and reverted commit 52e6b19. I then built the .deb packages for this modified kernel, installed them on my VM, and booted into the modified kernel. The problem vanished, with graphical performance again matching the 6.18 NixOS VM. No other changes were made to the kernel, so it seems that 52e6b19 is indeed the commit that introduced the regression compared to 6.18. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: xorg 1:7.7+26ubuntu1 ProcVersionSignature: Ubuntu 7.0.0-30.30-generic 7.0.12 Uname: Linux 7.0.0-30-generic x86_64 ApportVersion: 2.34.0-0ubuntu2 Architecture: amd64 BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log' CasperMD5CheckResult: pass CompositorRunning: None CurrentDesktop: XFCE Date: Thu Aug 20 17:57:32 2026 DistUpgraded: Fresh install DistroCodename: resolute DistroVariant: ubuntu GraphicsCard: InstallationDate: Installed on 2026-08-20 (1 days ago) InstallationMedia: Xubuntu Minimal 26.04 "Resolute Raccoon" - Release amd64 (20260423.1) Lspci: Lspci-vt: Lsusb: Error: command ['lsusb'] failed with exit code 1: Lsusb-t: Lsusb-v: Error: command ['lsusb', '-v'] failed with exit code 1: MachineType: Microsoft Corporation Virtual Machine ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no username) SHELL=/bin/bash TERM=xterm-256color XDG_RUNTIME_DIR=<set> ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-30-generic root=UUID=7ca2a92c-536c-4cd1-b534-487b767b4a3f ro quiet splash SourcePackage: xorg Symptom: display UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 10/23/2025 dmi.bios.release: 4.1 dmi.bios.vendor: Microsoft Corporation dmi.bios.version: Hyper-V UEFI Release v4.1 dmi.board.asset.tag: None dmi.board.name: Virtual Machine dmi.board.vendor: Microsoft Corporation dmi.board.version: Hyper-V UEFI Release v4.1 dmi.chassis.asset.tag: 6415-2400-6832-7400-3077-0046-58 dmi.chassis.type: 3 dmi.chassis.vendor: Microsoft Corporation dmi.chassis.version: Hyper-V UEFI Release v4.1 dmi.modalias: dmi:bvnMicrosoftCorporation:bvrHyper-VUEFIReleasev4.1:bd10/23/2025:br4.1:svnMicrosoftCorporation:pnVirtualMachine:pvrHyper-VUEFIReleasev4.1:rvnMicrosoftCorporation:rnVirtualMachine:rvrHyper-VUEFIReleasev4.1:cvnMicrosoftCorporation:ct3:cvrHyper-VUEFIReleasev4.1:skuNone:pfaVirtualMachine: dmi.product.family: Virtual Machine dmi.product.name: Virtual Machine dmi.product.sku: None dmi.product.version: Hyper-V UEFI Release v4.1 dmi.sys.vendor: Microsoft Corporation version.compiz: compiz N/A version.libdrm2: libdrm2 2.4.131-1 version.libgl1-mesa-dri: libgl1-mesa-dri 26.0.3-1ubuntu1 version.libgl1-mesa-glx: libgl1-mesa-glx N/A version.xserver-xorg-core: xserver-xorg-core 2:21.1.22-1ubuntu1 version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:22.0.0-1build2 version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20210115-1build2 version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.18-1build1 ** Affects: ubuntu Importance: Undecided Status: New ** Tags: amd64 apport-bug performance resolute ubuntu -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2164701 Title: Poor frame pacing under Hyper-V (blame kernel commit 52e6b19) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+bug/2164701/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
