[Bug 67970] Kernel bugs related to the powersaving features of mobility radeon x1400

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=67970

--- Comment #1 from Boris Gjenero <boris.gjenero at gmail.com> ---
I've seen the same things on my Inspiron 6400 with Radeon X1400 graphics,
running 64-bit Ubuntu 16.10 with kernel 4.8.0-26-generic. Though while playing
with it I saw some variations in behaviour. Sometimes in dynpm, reported
frequencies were from the last profile that was used. Sometimes, changing a
profile had no effect. Using vblank_mode=0 glxgears, Chrome and Firefox I am
unable to see a performance difference between low and mid. There is a very
definite difference between those and high profile. Performance of dynpm and
high profile is identical or very close.

Playing with these settings can introduce instability. After switching among
profiles, going back to dynpm usually causes brief bright flashes of the
screen. Those flashes never happen after setting dynpm in /etc/rc.local. Also,
changing to high profile caused a total hang once, where even Magic SysRq
didn't help. Yes, I also see NMIs switching to low, but those seem to have no
ill effect.

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