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[Launchpad Bug Tracker <1516565@xxxxxxxxxxxxxxxxxx>]

[Expired for linux (Ubuntu) because there has been no activity for 60
days.]

** Changed in: linux (Ubuntu)
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1516565

Title:
  Strange kernel or scheduling problem

Status in linux package in Ubuntu:
  Expired

Bug description:
  I see a strange kernel or scheduler problem with Kubuntu 15.04 and
  15.10.  I have Intel 3960X cpu with 6 cores (Hyperthreading is
  disabled). The problem is that when I run many CPU intensive
  applications (using full CPU), I cannot fully use all the cores of
  CPU. I tried a very simple app, which only multiplies some integers
  infinitly to emulate only high cpu usage with out any disk bottleneck.
  when I run multiple copies of the app, sometimes the scheduler assign
  all of them to a single core! Sometimes "top" shows that all CPU
  intensive apps are using only 0% CPU even though one of the cores is
  100% utilized and the apps are definitely working. Sometimes the apps
  cannot use the full CPU and the CPU usage of a single app oscillates
  between 0% to 100%. The problem becomes visible when there are 4 or
  more CPU intensive apps. When there are 6 apps, the mouse movement
  becomes sluggish and the system becomes very unresponsive even though
  the "top" shows that the CPUs are not fully used. I tried adding
  intel_pstate=disable in GRUB and setting scheduler to SCHED_ISO, but
  no effect.

  I tried different kernel versions previously installed. The current
  kernel 4.2.0 and the previous kernel 3.19.0 have this problem. Kernel
  version 3.11.0-19 worked without any problems.

  When I change a device driver( like the NVIDIA binary driver version),
  the problem is fixed until the next reboot. Probably changing a device
  driver is resetting the kernel and temporally fixing the problem.

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