Experimental Physics and
Industrial Control System

Gerrit Kühn via Tech-talk <[email protected]> · Thu, 2 May 2019 15:25:20 +0200

Dear all,

On a rather recent Linux installation I saw the strange issue that some of
our medm screens had channels that did not update properly. Most of the
affected displays used rectangles, often several of them stacked. When
opening the screen, many of these stayed white. Proper operation could be
triggered by forcing redraw of the screen by switching forth and back from
a different virtual desktop, but the rectabgles became white again when
changing the size of the window. Also, in some windows the wrong rectangle
(from multiple stacked ones) was displayed.

After trying a lot of things (comparing with other machines' displays,
using different window managers etc.), it turned out that the issue was
tied to the local display. Running medm over an ssh tunnel, just
displaying on a different machine, worked just fine.
In the end I could completely work around the issue by changing the
acceleration method for our Intel-Kabylake-driven monitors from the
default SNA to UXA by adding
Option      "AccelMethod" "uxa"
to the Xorg configuration. With that, everything appears to be back to
normal.

Admittedly, we don't use the latest medm version here (ours is 3.1.9), but
I briefly looked into the repository and saw no changes that seemed
releated to an issue like this. Did anybody already see something like
this before? In any case, this is for the record, if anybody else might
stumble upon this.

cu
  Gerrit

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System