Solved Intel i5 (sandy bridge) Flickering Display

Just recently upgraded all packages. Its really only been about 6 weeks since last full userland build. My userland after reboot was a flickering/flashing mess complete with video remnants/artifacts. It was TOTALLY "BORKED"! Code below outlines present state of system from KDE's point of view. To keep composting working using KDE5 has been painfull and time consuming involving other tweaks but this recent failure looked like it may involve a complete redo. Point of code post is to display present KDE5 version which is KWin version: 5.12.7. To restore rendering go to System Setting>Hardware>Display&Monitor>Compositor>Tearing Prevention>"and change to {Never}" from whatever you are presently using. Log out and back in. It worked like a charm for me. Posted here because it seems that Sandy Bridge is highly susceptible to this phenom, but may possibly exist in other hardware.

Code:
$ qdbus org.kde.KWin /KWin supportInformation
KWin Support Information:
The following information should be used when requesting support on e.g. http://forum.kde.org.
It provides information about the currently running instance, which options are used,
what OpenGL driver and which effects are running.
Please post the information provided underneath this introductory text to a paste bin service
like http://paste.kde.org instead of pasting into support threads.

==========================

Version
=======
KWin version: 5.12.7
Qt Version: 5.12.0
Qt compile version: 5.12.0
XCB compile version: 1.13.1

Operation Mode: X11 only

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: yes
HAVE_INPUT: yes
HAVE_DRM: yes
HAVE_GBM: yes
HAVE_X11_XCB: yes
HAVE_EPOXY_GLX: yes
HAVE_WAYLAND_EGL: yes

X11
===
Vendor: The X.Org Foundation
Vendor Release: 11804000
Protocol Version/Revision: 11/0
SHAPE: yes; Version: 0x11
RANDR: yes; Version: 0x14
DAMAGE: yes; Version: 0x11
Composite: yes; Version: 0x4
RENDER: yes; Version: 0xb
XFIXES: yes; Version: 0x50
SYNC: yes; Version: 0x31
GLX: yes; Version: 0x0

Decoration
==========
Plugin: org.kde.breeze
Theme:
Blur: 0
onAllDesktopsAvailable: true
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 2
decorationButtonsRight: 6, 3, 4, 5
borderSize: 3
gridUnit: 10
font: Noto Sans,10,-1,0,50,0,0,0,0,0,Regular
smallSpacing: 2
largeSpacing: 10

Platform
==========
Name: KWin::X11StandalonePlatform

Options
=======
focusPolicy: 0
nextFocusPrefersMouse: false
clickRaise: true
autoRaise: false
autoRaiseInterval: 0
delayFocusInterval: 0
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 4
focusPolicyIsReasonable: true
borderSnapZone: 10
windowSnapZone: 10
centerSnapZone: 0
snapOnlyWhenOverlapping: false
rollOverDesktops: true
focusStealingPreventionLevel: 0
legacyFullscreenSupport: false
operationTitlebarDblClick: 5000
operationMaxButtonLeftClick: 5000
operationMaxButtonMiddleClick: 5015
operationMaxButtonRightClick: 5014
commandActiveTitlebar1: 0
commandActiveTitlebar2: 30
commandActiveTitlebar3: 2
commandInactiveTitlebar1: 4
commandInactiveTitlebar2: 30
commandInactiveTitlebar3: 2
commandWindow1: 7
commandWindow2: 8
commandWindow3: 8
commandWindowWheel: 31
commandAll1: 10
commandAll2: 3
commandAll3: 14
keyCmdAllModKey: 16777251
showGeometryTip: false
condensedTitle: false
electricBorderMaximize: true
electricBorderTiling: true
electricBorderCornerRatio: 0.25
borderlessMaximizedWindows: false
killPingTimeout: 5000
hideUtilityWindowsForInactive: false
inactiveTabsSkipTaskbar: false
autogroupSimilarWindows: false
autogroupInForeground: true
compositingMode: 1
useCompositing: true
compositingInitialized: true
hiddenPreviews: 1
glSmoothScale: 1
xrenderSmoothScale: false
maxFpsInterval: 16666666
refreshRate: 0
vBlankTime: 6000000
glStrictBinding: true
glStrictBindingFollowsDriver: true
glCoreProfile: true
glPreferBufferSwap: 0
glPlatformInterface: 1
windowsBlockCompositing: false

Screen Edges
============
desktopSwitching: false
desktopSwitchingMovingClients: false
cursorPushBackDistance: 1x1
timeThreshold: 150
reActivateThreshold: 350
actionTopLeft: 0
actionTop: 0
actionTopRight: 3
actionRight: 0
actionBottomRight: 4
actionBottom: 0
actionBottomLeft: 0
actionLeft: 0

Screens
=======
Multi-Head: no
Active screen follows mouse:  no
Number of Screens: 1

Screen 0:
---------
Name: LVDS1
Geometry: 0,0,1366x768
Scale: 1
Refresh Rate: 60.0022


Compositing
===========
Compositing is active
Compositing Type: OpenGL
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Mobile
OpenGL version string: 3.3 (Core Profile) Mesa 18.1.9
OpenGL platform interface: GLX
OpenGL shading language version string: 3.30
Driver: Intel
GPU class: SandyBridge
OpenGL version: 3.3
GLSL version: 3.30
Mesa version: 18.1.9
X server version: 1.18.4
Direct rendering: Requires strict binding: yes
GLSL shaders:  yes
Texture NPOT support:  yes
Virtual Machine:  no
OpenGL 2 Shaders are used
Painting blocks for vertical retrace:  no

Loaded Effects:
---------------
kwin4_effect_windowaperture
kwin4_effect_translucency
kwin4_effect_scalein
kwin4_effect_maximize
kwin4_effect_logout
kwin4_effect_fade
kwin4_effect_dialogparent
slidingpopups
wobblywindows
slideback
screenshot
minimizeanimation
glide
desktopgrid
cubeslide
cube
colorpicker
sheet
presentwindows
highlightwindow
fallapart
contrast
startupfeedback
screenedge
kscreen

Currently Active Effects:
-------------------------
contrast

Effect Settings:
----------------
kwin4_effect_windowaperture:

kwin4_effect_translucency:

kwin4_effect_scalein:

kwin4_effect_maximize:

kwin4_effect_logout:

kwin4_effect_fade:

kwin4_effect_dialogparent:

slidingpopups:
fadeInTime: 150
fadeOutTime: 250

wobblywindows:
stiffness: 0.15
drag: 0.8
moveFactor: 0.1
xTesselation: 20
yTesselation: 20
minVelocity: 0
maxVelocity: 1000
stopVelocity: 0.5
minAcceleration: 0
maxAcceleration: 1000
stopAcceleration: 0.5
moveEffectEnabled: true
openEffectEnabled: false
closeEffectEnabled: false
moveWobble: true
resizeWobble: true

slideback:

screenshot:

minimizeanimation:

glide:
duration: 350
effect: 1
angle: -90

desktopgrid:
zoomDuration: 300
border: 10
desktopNameAlignment: 0
layoutMode: 0
customLayoutRows: 2
usePresentWindows: true

cubeslide:
rotationDuration: 300
dontSlidePanels: true
dontSlideStickyWindows: false
usePagerLayout: true
useWindowMoving: false

cube:
cubeOpacity: 0.800000011920929
opacityDesktopOnly: false
displayDesktopName: true
reflection: true
rotationDuration: 500
backgroundColor: #000000
capColor: #31363b
paintCaps: true
closeOnMouseRelease: false
zPosition: 100
useForTabBox: false
invertKeys: false
invertMouse: false
capDeformationFactor: 0
useZOrdering: false
texturedCaps: true

colorpicker:

sheet:
duration: 500

presentwindows:
layoutMode: 0
showCaptions: true
showIcons: true
doNotCloseWindows: false
ignoreMinimized: false
accuracy: 20
fillGaps: true
fadeDuration: 150
showPanel: false
leftButtonWindow: 1
rightButtonWindow: 2
middleButtonWindow: 0
leftButtonDesktop: 2
middleButtonDesktop: 0
rightButtonDesktop: 0

highlightwindow:

fallapart:
blockSize: 40

contrast:

startupfeedback:
type: 1

screenedge:

kscreen:
 
Just recently upgraded all packages. Its really only been about 6 weeks since last full userland build. My userland after reboot was a flickering/flashing mess complete with video remnants/artifacts. It was TOTALLY "BORKED"! Code below outlines present state of system from KDE's point of view. To keep composting working using KDE5 has been painfull and time consuming involving other tweaks but this recent failure looked like it may involve a complete redo. Point of code post is to display present KDE5 version which is KWin version: 5.12.7. To restore rendering go to System Setting>Hardware>Display&Monitor>Compositor>Tearing Prevention>"and change to {Never}" from whatever you are presently using. Log out and back in. It worked like a charm for me. Posted here because it seems that Sandy Bridge is highly susceptible to this phenom, but may possibly exist in other hardware

Thanks for this info, I can confirm that it's also relevant for Haswell.

I'm running KDE on an 11.2 system with an I5-4460. After a recent package upgrade it became totally unusable, after logging in from sddm the screen flickered and wouldn't respond to mouse clicks because it displayed part of the sddm login display in place of the required window content. The situation was so bad that I wasn't even able to run System Settings. Fortunately I was able to roll back to an earlier ZFS boot environment where I could run System Setting and set Tearing Prevention to 'never'. This completely cured the problem when I rebooted back into the newer boot environment.

For the benefit of anyone unable to rollback to an earlier working version you can fix this from a terminal console by editing ~/.config/kwinrc and changing the value of GLPreferBufferSwap in the compositing] section to n
 
I have the same issue. Looks like driver problem though. Today I upgraded rather old (probably october) port tree, so I have both DRM and KDE changes. Switching off VSync worked for me too. Hello, tearing :(
I'd remove Solved icon, this is a regression.

Code:
drm-fbsd12.0-kmod-4.16.g20181215
drm-kmod-g20181126

FreeBSD 12.0-RELEASE
CPU: Intel(R) Core(TM) i7-6560U CPU @ 2.20GHz (2208.09-MHz K8-class CPU)

Xorg version X.Org X Server 1.19.6 (from 196678), modesetting with default options
 
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