[Bug 81021] AMD CPUs w/ Integrated Graphics (APUs) And Turbo Core Only Boost If "fglrx" Module Is Loaded

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Sun Aug 3 10:34:01 PDT 2014


--- Comment #7 from LiNuxXer <andre.d at gmx.net> ---
Hello Alex,

(In reply to Alex Deucher from comment #6)
> Turbo Core (bapm) is controlled by a microcontroller on the APU.  The same
> microcontroller also manages the GPU power management.  On most APU systems,
> turbo core is enabled by default by the sbios, but apparently on your system
> it's not.  Maybe there is a bios option to enable it by default on your
> system.

reconsidering everything you wrote and I thought I found out, I think I'll have
to start from scratch.

Firstly, the BIOS does have Turbo Core and Cool'n'Quiet settings, along with
many others. Also. it's the latest version, and the A10-6700 is not brand new.

Secondly, I noticed that even Ubuntu Server will install the radeon driver
although there is no need to.

Thirdly, I made a quick test with a Gentoo installer (which neither loads the
radeon module nor sets the ondemand governor) and an amperemeter (to be honest:
two amperemeters, because I couldn't believe the results), and this completely
confused me. While the system needs 96 W while in the BIOS, this drops to 56 W
as soon as Linux boots. And I can't get a lower power consumption even if I set
the ondemand governor, with the freq of the four cores shown to drop from 3700
to 1800. Several reviews mention a 35 W system (!) power consumption when the
A10-6700 is idle, but in this setup, the changing frequency does not have the
slightest effect (which it should even have with an average power supply).

I was wondering whether you could shed some additional light on this. How many
settings actually influence this behaviour in total (since the BIOS also has
"Cool'n'Qiet")? Is there any tool to display them? If not, would you help me to
build one? Could we see some incomplete initialisation here? Is there any
documentation on these settings? I'm groping in the dark here with no progress,
and I may even have to exchange the HW if I don't get near the 35 W and have
Turbo Core.

> When the GPU driver loads and sets up the GPU power management, it
> can also enable or disable bapm.  When bapm and GPU power mangement (dynamic
> GPU engine clock and voltage scaling, clock and powergating, etc.) are both
> enabled, some systems have stability problems (sudden reboots, hangs,
> graphical corruption, issues when switching between AC and battery).

I would be happy with some fixed low bandwidth setting for the graphics. Saw
some indivation for 33 MHz during console mode but am not sure I can rely on
this information.

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