Public bug reported: Not sure if this is an issue with the X server or with the kernel i915 module, so I'm starting with X.
The system is a Thinkpad X1 Carbon, Gen 7. Details on the graphics hardware (from lspci -vv) are below. BIOS is up-to-date as of Nov. 21. The symptom is that X will not redraw screen state for several seconds at a time under certain circumstances. Characters typed into a window, or an application that attempts to redraw regularly, are the easiest demonstration of this. E.g. running 'vmstat 1' in a terminal (which should print one line of text every second), I see no activity for roughly 5 seconds, and then all 5 seconds worth of content are printed. Generating some activity with the mouse/trackpad seems to trigger a refresh before the full time delay expires. This problem does *not* occur in the default Ubuntu GNOME environment. It appears that it only occurs when there are no GL clients running. In a minimal "failsafe" X session, it is reproducible 100% of the time. In a failsafe session with the "glxdemo" program from the "mesa-utils" package installed, the problem does not occur. I suspect that there's enough GL usage in the standard GNOME configuration that this doesn't affect most users, but my default X session doesn't use much GL. 00:02.0 VGA compatible controller: Intel Corporation UHD Graphics 620 (Whiskey Lake) (rev 02) (prog-if 00 [VGA controller]) Subsystem: Lenovo Device 2292 Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+ Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- Latency: 0 Interrupt: pin A routed to IRQ 130 Region 0: Memory at e9000000 (64-bit, non-prefetchable) [size=16M] Region 2: Memory at c0000000 (64-bit, prefetchable) [size=256M] Region 4: I/O ports at 2000 [size=64] [virtual] Expansion ROM at 000c0000 [disabled] [size=128K] Capabilities: [40] Vendor Specific Information: Len=0c <?> Capabilities: [70] Express (v2) Root Complex Integrated Endpoint, MSI 00 DevCap: MaxPayload 128 bytes, PhantFunc 0 ExtTag- RBE+ DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported- RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop- MaxPayload 128 bytes, MaxReadReq 128 bytes DevSta: CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr- TransPend- DevCap2: Completion Timeout: Not Supported, TimeoutDis-, LTR-, OBFF Not Supported DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit- Address: fee00018 Data: 0000 Capabilities: [d0] Power Management version 2 Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-) Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME- Capabilities: [100 v1] Process Address Space ID (PASID) PASIDCap: Exec- Priv-, Max PASID Width: 14 PASIDCtl: Enable- Exec- Priv- Capabilities: [200 v1] Address Translation Service (ATS) ATSCap: Invalidate Queue Depth: 00 ATSCtl: Enable-, Smallest Translation Unit: 00 Capabilities: [300 v1] Page Request Interface (PRI) PRICtl: Enable- Reset- PRISta: RF- UPRGI- Stopped+ Page Request Capacity: 00008000, Page Request Allocation: 00000000 Kernel driver in use: i915 Kernel modules: i915 ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: xserver-xorg-core-hwe-18.04 2:1.20.4-1ubuntu3~18.04.1 ProcVersionSignature: Ubuntu 5.3.0-19.20~18.04.2-generic 5.3.1 Uname: Linux 5.3.0-19-generic x86_64 ApportVersion: 2.20.9-0ubuntu7.9 Architecture: amd64 Date: Thu Nov 21 17:12:15 2019 InstallationDate: Installed on 2019-11-15 (6 days ago) InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805) ProcEnviron: TERM=xterm PATH=(custom, user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/zsh SourcePackage: xorg-server-hwe-18.04 UpgradeStatus: No upgrade log present (probably fresh install) ** Affects: xorg-server-hwe-18.04 (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug bionic -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg-server-hwe-18.04 in Ubuntu. https://bugs.launchpad.net/bugs/1853542 Title: X hangs for several seconds periodically when no GL clients are open To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg-server-hwe-18.04/+bug/1853542/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp