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[Bug 1531951] Re: A severe performance degradation while syncing md raid after the upgrade to 15.10


Pavol Domin, in order to maximize the probability of upstream addressing
this issue as fast as possible, you would want to fully commit bisect
from kernel 3.19 to 4.2 in order to identify the last good kernel
commit, followed immediately by the first bad one. Could you please do
this at your convenience following
https://wiki.ubuntu.com/Kernel/KernelBisection ?

Please note, finding adjacent kernel versions is not fully commit

Thank you for your understanding.

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  A severe performance degradation while syncing md raid after the
  upgrade to 15.10

Status in linux package in Ubuntu:

Bug description:
  I run Ubuntu from the fakerade (imsm) raid5 volume. If the volume is
  syncing, the system response is severely degraded. There is no problem
  if I boot the same system from the previous kernel 3.19.0-32. Some

  [md125_resync] kernel thread CPU consumption: 94 per-mill compared to 10 in 3.19 kernel
  [md125_raid5] kernel thread CPU consumption: 243 per-mill compared to 86 in 3.19 kernel
  1MB direct read from md array: 0.5s compared to 0.01s in 3.19 kernel
  1MB direct read from md raid member: 2.2s compared to 0.02s in 3.19 kernel

  As a result, it's practically impossible to work in 4.2 kernel if md
  raid is syncing (even the boot takes several minutes here), whereas in
  3.19 I don't feel any performance degradation at all, regardless the
  raid volume is syncing or not.

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: linux-image-4.2.0-22-generic 4.2.0-22.27
  ProcVersionSignature: Ubuntu 4.2.0-22.27-generic 4.2.6
  Uname: Linux 4.2.0-22-generic x86_64
  NonfreeKernelModules: nvidia
  ApportVersion: 2.19.1-0ubuntu5
  Architecture: amd64
   /dev/snd/controlC1:  palo       3869 F.... pulseaudio
   /dev/snd/pcmC0D0p:   palo       3869 F...m pulseaudio
   /dev/snd/controlC0:  palo       3869 F.... pulseaudio
  CurrentDesktop: Unity
  Date: Thu Jan  7 18:51:39 2016
  HibernationDevice: RESUME=UUID=f9900a93-c16d-4cae-9098-194fdf3abbfe
  InstallationDate: Installed on 2011-09-16 (1574 days ago)
  InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release amd64 (20110427.1)
  MachineType: System manufacturer System Product Name
  ProcFB: 0 VESA VGA
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.2.0-22-generic root=/dev/mapper/vg00-lv_ubuntu_root ro init=/sbin/upstart
   linux-restricted-modules-4.2.0-22-generic N/A
   linux-backports-modules-4.2.0-22-generic  N/A
   linux-firmware                            1.149.3
  SourcePackage: linux
  UpgradeStatus: Upgraded to wily on 2016-01-02 (4 days ago)
  dmi.bios.date: 02/23/2009
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 2102
  dmi.board.asset.tag: To Be Filled By O.E.M.
  dmi.board.name: P5Q-PRO
  dmi.board.vendor: ASUSTeK Computer INC.
  dmi.board.version: Rev 1.xx
  dmi.chassis.asset.tag: Asset-1234567890
  dmi.chassis.type: 3
  dmi.chassis.vendor: Chassis Manufacture
  dmi.chassis.version: Chassis Version
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2102:bd02/23/2009:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnP5Q-PRO:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
  dmi.product.name: System Product Name
  dmi.product.version: System Version
  dmi.sys.vendor: System manufacturer

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