[Bug 516325] Re: ACPI: enable C2 and Turbo-mode on Nehalem notebooks on A/C

[Stefan Bader]

** Changed in: linux (Ubuntu Karmic)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu Karmic)
       Status: New => Fix Committed

** Changed in: linux (Ubuntu Karmic)
     Assignee: (unassigned) => Stefan Bader (stefan-bader-canonical)

** Changed in: linux (Ubuntu)
       Status: Triaged => Fix Committed

** Changed in: linux (Ubuntu)
     Assignee: (unassigned) => Andy Whitcroft (apw)

** Description changed:

+ SRU Justification:
+ 
+ Impact: Not entering deeper C-states causes more heat and can cause
+ systems to throttle or even to shut down.
+ 
+ Fix: This has been backported from upstream and made it into 2.6.32.7
+ for Lucid. It looks simple enough to not cause regressions.
+ 
+ ---
+ 
  Please backport the following patch into Karmic:
  
  http://lkml.org/lkml/2010/1/26/368
  
  From: Len Brown <len.brown at intel.com>
  
  upstream in 2.6.33-rc:  5d76b6f6c17572e662f5c99c2023adae92100855
  
  Refreshed here for 2.6.32.y, applies w/ offset back to 2.6.29.y.
  
  Linux has always ignored ACPI BIOS C2 with exit latency > 100 usec,
  and the ACPI spec is clear that is correct FADT-supplied C2.
  However, the ACPI spec explicitly states that _CST-supplied C-states
  have no latency limits.
  
  So move the 100usec C2 test out of the code shared
  by FADT and _CST code-paths, and into the FADT-specific path.
  
  This bug has not been visible until Nehalem, which advertises
  a CPU-C2 worst case exit latency on servers of 205usec.
  That (incorrect) figure is being used by BIOS writers
  on mobile Nehalem systems for the AC configuration.
  Thus, Linux ignores C2 leaving just C1, which is
  saves less power, and also impacts performance
  by preventing the use of turbo mode.
  
  http://bugzilla.kernel.org/show_bug.cgi?id=15064

-- 
ACPI: enable C2 and Turbo-mode on Nehalem notebooks on A/C
https://bugs.launchpad.net/bugs/516325
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