[kwlug-disc] AMD FX-8320 + Turbo mode + CPU frequency scaling

[William Park]

To those struggling with AMD FX cpu and CPU frequency scaling...

Background:

    I waited for Intel X99/LGA2011-E.  Good specs to last you for many
    many years.  The price, however... nut!  So, I upgraded to AMD
    FX-8320 (8-core, 3.5GHz base, 4.0GHz turbo) for $150.

    It would lock up at 3.5GHz, 3.2GHz, and even 2.9GHz.  I just
    couldn't figure it out.  It wasn't heat or memory.  It would be sort
    of stable below 2.9GHz, and more stable with "cpufreq" and "Turbo"
    turned off.  After 1 week of swearing, I found that AMD's Turbo mode
    and kernel's CPU frequency scaling don't like each other.

Solution:

    - Disable kernel CPU frequency scaling (ie. don't load cpufreq_*)
    - Set BIOS to the lowest frequency (800MHz for me)
    - Enable AMD Turbo mode in BIOS, and let it adjust CPU frequency and
      voltage internally.

Conclusion:

    According to /proc/cpuinfo and 'cpufreq-info', my machine is 8-core @
    800MHz.  But, in reality, it would be anywhere between 800MHz and 4GHz.
    It feels like 4GHz for light load, 3GHz for heavy load, and 800MHz for
    idle.
-- 
William