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[Doug Smythies <1233479@xxxxxxxxxxxxxxxxxx>]

All active cores share the same frequency. This is one of the misleading
things about the acpi-cpufreq driver, it tends to show target
frequencies not actual frequencies.

See also the "Intel 2nd gen core desktop vol 1 datasheet" - Chapter 4
Power Management - Section 4.2 Processor Core Power Management - Sub-
section 1 Enhanced Intel SpeedStep Technology - Bullet point 2 - 3rd
sub-list entry (page 46 of the html or pdf):

"All active processor cores share the same frequency and voltage. In a
multicore processor, the highest frequency P-state requested amongst all
active cores is selected. "

ref:  http://www.intel.com/content/www/us/en/processors/core/2nd-gen-
core-desktop-vol-1-datasheet.html

I do not know if anything was patched for Ubuntu's 3.11 kernel. I tested
many, but not all, of the 3.11RC series, both Ubuntu and from
kernel.org, but I was mainly working with the intel_pstate driver, and
only using the acpi-cpufreq driver for comparative tests.

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https://bugs.launchpad.net/bugs/1233479

Title:
  ondemand cpufreq governor does not scale CPU freq on Sandybridge

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  I notice that turbostat shows all cpus stuck at the minimum 800MHz
  (see attached log) on my system, even after rebooting twice. I used
  "stress --cpu 8" to confirm that the frequencies remained at 800MHz
  even under load.

  It looks like the system is using the acpi-cpufreq driver with the
  ondemand governor (has the default been changed so it does not use
  intel p-state, as per
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1188647?).

  
  Edit: See comment #1 below - it looks like I can manually change the cpu freq, but the governor cannot. Also, switching to use intel pstate fixes the problem.

  
  The only unusual thing I had done prior to this was to boot into the weekly build of 3.12-rc3 just prior (this kernel kept the frequencies rather high, typically over 2GHz, ie using a lot more power than usual, so I rebooted back into the standard kernel).

  This is the contents of the files in
  /sys/devices/system/cpu/cpu0/cpufreq/:

  affected_cpus:
  0
  bios_limit:
  2001000
  cpuinfo_cur_freq:
  800000
  cpuinfo_max_freq:
  2001000
  cpuinfo_min_freq:
  800000
  cpuinfo_transition_latency:
  10000
  freqdomain_cpus:
  0 1 2 3 4 5 6 7
  related_cpus:
  0
  scaling_available_frequencies:
  2001000 2000000 1900000 1800000 1700000 1600000 1500000 1400000 1300000 1200000 1100000 1000000 900000 800000
  scaling_available_governors:
  conservative ondemand userspace powersave performance
  scaling_cur_freq:
  800000
  scaling_driver:
  acpi-cpufreq
  scaling_governor:
  ondemand
  scaling_max_freq:
  2001000
  scaling_min_freq:
  800000
  scaling_setspeed:
  <unsupported>
  stats:

  ProblemType: Bug
  DistroRelease: Ubuntu 13.10
  Package: linux-image-3.11.0-9-generic 3.11.0-9.16
  ProcVersionSignature: Ubuntu 3.11.0-9.16-generic 3.11.2
  Uname: Linux 3.11.0-9-generic x86_64
  ApportVersion: 2.12.5-0ubuntu1
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  rocko      2813 F.... pulseaudio
  Date: Tue Oct  1 10:13:24 2013
  InstallationDate: Installed on 2012-08-25 (401 days ago)
  InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120724.2)
  MachineType: Dell Inc. Dell System XPS L502X
  MarkForUpload: True
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.11.0-9-generic root=UUID=67083065-b92e-4596-a218-817c1dfc8ae7 ro crashkernel=384M-2G:64M,2G-:128M quiet splash vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.11.0-9-generic N/A
   linux-backports-modules-3.11.0-9-generic  N/A
   linux-firmware                            1.115
  SourcePackage: linux
  UpgradeStatus: Upgraded to saucy on 2013-09-01 (30 days ago)
  dmi.bios.date: 05/29/2012
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: A11
  dmi.board.name: 0NJT03
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 8
  dmi.chassis.vendor: Dell Inc.
  dmi.chassis.version: 0.1
  dmi.modalias: dmi:bvnDellInc.:bvrA11:bd05/29/2012:svnDellInc.:pnDellSystemXPSL502X:pvr:rvnDellInc.:rn0NJT03:rvrA00:cvnDellInc.:ct8:cvr0.1:
  dmi.product.name: Dell System XPS L502X
  dmi.sys.vendor: Dell Inc.

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