Rebuilt System on Identical Hardware - Getting VLC Tearing

[Vorlon]

I use a Lenovo ThinkCentre desktop (Intel i5, 8 GBytes RAM) for my video server, playing recorded videos using VLC at 2160p with no trouble. My gentoo installation is about 3 years old, but regularly updated to stable (ACCEPT_KEYWORDS=amd64). The profile is the now-obsolete default "/linux/amd64/17.1/desktop".

I've had trouble updating profiles, so instead of updating it to the new profile, I used a second identical ThinkCentre I had to build a duplicate system. I used the same .config file to build the monolithic kernel, the same make.conf file, and loaded the same programs on both machines.

But now I get very bad tearing of videos when being played by VLC.

Things I've checked:

• Same .config for the monolithic kernel
  
• Same make.conf for portage
  
• I'm using the same i915 kernel module in both
  
• I'm loading the same graphic driver (glamoregl) in X on both machines. (they both also load glx & fb)
  
• Both machines report the same hardware using lspci.
  
• Both use Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controllers
  
• No apparent errors in syslog
  
• No apparent errors in dmesg
  

I've noted these differences between the 2 systems:

• Converted from profile 17.1 to 23.0
  
• The new system boots via UEFI, while the old one booted using the old legacy method.
  
• Pulseaudio is in use on the new system
  
• Good system uses VLC version 3.0.20-r11. The Bad system uses VLC version 3.0.21
  
• VLC USE flags are different (presumably due to the new profile). There are more flags used on the new system. The good system uses "X alsa dbus dvbpsi encode fdk ffmpeg gcrypt gui libsamplerate ncurses run-as-root ssl". The bad system uses "X alsa dbus dvbpsi dvd encode fdk ffmpeg gcrypt gui jpeg libnotify libsamplerate mad ncurses pulseaudio run-as-root ssl truetype udev wayland x264 xml"
  
• Good system used kernel 6.6.47-gentoo. Bad uses 6.6.52-gentoo
  

I would appreciate suggestions of things to check or ways to improve video playback performance.

TIA!
_________________
Casey Bralla
Chief Nerd in Residence
The NerdWorld Organisation