Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: How Well Is AMD CnQ Working For You On Linux?

Hybrid View

  1. #1
    Join Date
    Jan 2007
    Posts
    14,651

    Default How Well Is AMD CnQ Working For You On Linux?

    Phoronix: How Well Is AMD CnQ Working For You On Linux?

    One of the latest possible Linux power-related regressions I've heard about is that AMD Cool 'n' Quiet may no longer be functioning too well on Linux-based systems...

    http://www.phoronix.com/vr.php?view=MTIxNjE

  2. #2
    Join Date
    Sep 2008
    Location
    Vilnius, Lithuania
    Posts
    2,541

    Default

    The only device with an AMD processor that I have right now is a Brazos-based netbook, and it doesn't seem to have any power management issues. If anything, it exceeds the specifications. I didn't check the power management when CnQ was disabled, though.

    That said, isn't CnQ/EIST losing is relevance lately, in light of ACPI processor (C) states? If nothing is using resources, it just goes to complete sleep by itself. No need to change the frequency, so there is no performance loss.

  3. #3
    Join Date
    Sep 2012
    Posts
    5

    Default asus f1a75-M pro

    I have a f1a75-M pro in combination with AMD's A8-3870K and after enabling the powernow or any other power saving function in bios the system will locks up. No idea if this is due to the hardware or linux.
    Mard0

  4. #4
    Join Date
    Jan 2010
    Posts
    364

    Default

    Quote Originally Posted by mard0 View Post
    I have a f1a75-M pro in combination with AMD's A8-3870K and after enabling the powernow or any other power saving function in bios the system will locks up. No idea if this is due to the hardware or linux.
    Mard0
    If PowerNow leads to lockups, this is almost certainly a hardware or BIOS issue. On K10 and later CPU generations, p-state transitioning is done in hardware, so there's little chance for any driver to screw up.

    PowerNow really did suck on K8 generation CPUs, but it's great on later CPUs.

  5. #5
    Join Date
    Dec 2010
    Location
    MA, USA
    Posts
    1,273

    Default

    I got the impression C'n'Q is and always has been a BIOS related thing, not OS, so i don't see why linux wouldn't use it. I guess depending on how you load the CPU, other OSes compared to windows might not use it as effectively but in the end, its how much power your system draws when idle that matters most.

  6. #6
    Join Date
    Jun 2012
    Posts
    320

    Default For me it's perfect.

    Quote Originally Posted by schmidtbag View Post
    I got the impression C'n'Q is and always has been a BIOS related thing, not OS, so i don't see why linux wouldn't use it. I guess depending on how you load the CPU, other OSes compared to windows might not use it as effectively but in the end, its how much power your system draws when idle that matters most.
    For me C'n'Q works perfectly. It keeps my FX8120 CPU at almost room themperature most of time even at low cooler speed. Really remarkable efficiency I admit. Yet that CPU is able to offer quite impressive performance when it's actually needed. The only thing I wish: AMD GPUs should work the very same ways with Linux opensource drivers. Unfortunately it's not a case so far

  7. #7
    Join Date
    Jun 2009
    Posts
    2,927

    Default

    Quote Originally Posted by 0xBADCODE View Post
    For me C'n'Q works perfectly. It keeps my FX8120 CPU at almost room themperature most of time even at low cooler speed. Really remarkable efficiency I admit. Yet that CPU is able to offer quite impressive performance when it's actually needed. The only thing I wish: AMD GPUs should work the very same ways with Linux opensource drivers. Unfortunately it's not a case so far
    I really do suspect that AMD will find a way to get proper powersaving out for their GPUs. Now that they are putting them onto the same die with the CPU, having them run on full blast all the time (and thus negating nearly all powersaving done by the CPU) is a big problem.

    Since these APUs were one of the driving forces behind releasing documentation and OSS drivers (the way I undestand it, at least), having them not work properly is not a good way to proceed. So I'm guessing that proper powersaving (already written) will be released once the technical review is done.

  8. #8
    Join Date
    Jan 2010
    Posts
    364

    Default

    Quote Originally Posted by schmidtbag View Post
    I got the impression C'n'Q is and always has been a BIOS related thing, not OS, so i don't see why linux wouldn't use it.
    It's really not, at least not entirely. What the BIOS needs to do for PowerNow/CnQ to work is fill the p-state table in the CPU's model-specific registers, and that's it. This table contain values for operating frequency, voltage, etc. for all states. The OS requires a driver that reads the table and instructs the CPU to switch to a certain state, depending on load, according to some governor. (BTW, if the BIOS fails to set up the p-state table correctly, you can do that from userspace before loading PowerNow drivers.) The transition between states is handled by the CPU itself, so the driver is quite simple.

    Earlier on K8, the driver also needed to accurately do and time all the nitty-gritty low-level details of transitioning between states, and this was quite error-prone, depending on hardware.
    Last edited by brent; 10-28-2012 at 11:15 AM.

  9. #9
    Join Date
    Mar 2011
    Posts
    377

    Default

    I just upgraded my kernel from 3.6 to 3.7-rc3 and wondered why CnQ stopped working at all, so I looked into the boot messages and found:
    powernow-k8: this CPU is not supported anymore, using acpi-cpufreq instead.
    As I didn't had acpi-cpufreq compiled into the kernel the issue was found.

    Not sure if I would call that a bad thing through. CPU is:
    model name : AMD Athlon(tm) II X3 455 Processor

  10. #10
    Join Date
    Aug 2013
    Location
    Germany
    Posts
    1

    Default

    Quote Originally Posted by brent View Post
    It's really not, at least not entirely. What the BIOS needs to do for PowerNow/CnQ to work is fill the p-state table in the CPU's model-specific registers, and that's it. This table contain values for operating frequency, voltage, etc. for all states. The OS requires a driver that reads the table and instructs the CPU to switch to a certain state, depending on load, according to some governor. (BTW, if the BIOS fails to set up the p-state table correctly, you can do that from userspace before loading PowerNow drivers.) The transition between states is handled by the CPU itself, so the driver is quite simple.

    Earlier on K8, the driver also needed to accurately do and time all the nitty-gritty low-level details of transitioning between states, and this was quite error-prone, depending on hardware.
    Hi brent I stumbled upon your post while searching the web for a way to fix a problem with my Laptop. I've got a MEDION E1312 with an AMD Sempron 210U and I'm using PeppermintOS 4 based on Ubuntu Kernel 3.8.0.29-generic.
    There are no BIOS Updates availlable from OEM and with my computer your mentioned situation fits my Problem: "BIOS fails to set up the p-state table correctly".
    So how do I setup p-states via userspace? Thanx in advance.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •