https://bugs.freedesktop.org/show_bug.cgi?id=99195
--- Comment #10 from Damian Nowak nowaker@geozone.pl --- Hey @Michel, I'll chime in. I've had Radeon HD 7870 for several years now. "ring 0/3 stalled for more than 10000+msecs" was my worst nightmare for quite some time (see https://bugs.freedesktop.org/show_bug.cgi?id=65963).
Some Mesa versions were totally broken because of this happening way too often (as in #65963). Most Mesa versions were good, as in: it doesn't happen *that* often but still happens (e.g. every month or so). Such a low occurrence rate of the error makes debugging or bisecting not possible, thus it's not even worth reporting it here and taking Michel's or Alex's time. But yet - yes, it does happen every once in a while.
Over the years, here's what I found to be a factor in ring 0/3 stalling, and by a "factor", I mean something that makes this problem happen a little more often than normally but still beyond reproducibility.
1. radeon.dpm=1 2. switching screens (CTRL+ALT+F1..F7)
Hope this helps, somehow.