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[Bug 1260112] Re: CPU stuck on minimum frequency after resume from suspend and unplugged


OK, so for a more scientific test. I used sysbench to test CPU
performance. I tested with the stock 3.11.0-15-generic kernel and the
test 3.13.0-031300rc3-generic kernel, both before and resume a
suspend/resume cycle.

The command i used to perform the tests: 
sysbench --num-threads=8 --test=cpu --cpu-max-prime=50000 run

The results:

3.11.0-15-generic: 12.4127s
3.11.0-15-generic (after suspend): 78.8023s

3.13.0-031300rc3-generic: 12.2202s
3.13.0-031300rc3-generic (after suspend): 35.0208s

We can very similar performance before suspend and degradation after
resume. A huge degradation with 3.11 (about 6.5x slower) and a smaller
one (about 3x slower) with 3.13.

Hope these help.

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  CPU stuck on minimum frequency after resume from suspend and unplugged

Status in “linux” package in Ubuntu:

Bug description:
  This happens on a Dell Latitude E6540 (4th gen core i7 CPU).

  Steps to reproduce:

  1) normally boot the computer and make sure  everything works as expected (i use the ondemand governor)
  2) suspend
  3) make the computer is unplugged and resume

  Expected behavior: cpu should work normally
  Actual behavior: cpu always stays at minimum frequency (in my case 800 MHz)

  If i resume from suspend while plugged to the AC charger, everything works as expected.
  ApportVersion: 2.12.5-0ubuntu2.2
  Architecture: amd64
   /dev/snd/controlC1:  gjm        2337 F.... pulseaudio
   /dev/snd/controlC0:  gjm        2337 F.... pulseaudio
  DistroRelease: Ubuntu 13.10
  HibernationDevice: RESUME=UUID=98df70b7-f534-4ef6-8647-8e98200ccd64
  InstallationDate: Installed on 2013-12-06 (4 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
  MachineType: Dell Inc. Latitude E6540
  MarkForUpload: True
  Package: linux (not installed)
   0 inteldrmfb
   1 radeondrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.11.0-15-generic.efi.signed root=UUID=22510d0e-a296-4b0f-a97a-27cb89a65419 ro quiet splash vt.handoff=7
  ProcVersionSignature: Ubuntu 3.11.0-15.23-generic 3.11.10
   linux-restricted-modules-3.11.0-15-generic N/A
   linux-backports-modules-3.11.0-15-generic  N/A
   linux-firmware                             1.116
   0: phy0: Wireless LAN
   	Soft blocked: no
   	Hard blocked: no
  Tags:  saucy
  Uname: Linux 3.11.0-15-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  dmi.bios.date: 09/03/2013
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: A05
  dmi.board.name: 0725FP
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 9
  dmi.chassis.vendor: Dell Inc.
  dmi.modalias: dmi:bvnDellInc.:bvrA05:bd09/03/2013:svnDellInc.:pnLatitudeE6540:pvr01:rvnDellInc.:rn0725FP:rvrA00:cvnDellInc.:ct9:cvr:
  dmi.product.name: Latitude E6540
  dmi.product.version: 01
  dmi.sys.vendor: Dell Inc.

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