kernel-packages team mailing list archive

[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

Would it be possible for you to test the latest upstream kernel? Refer
to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest
v4.3 kernel[0].

If this bug is fixed in the mainline kernel, please add the following
tag 'kernel-fixed-upstream'.

If the mainline kernel does not fix this bug, please add the tag:
'kernel-bug-exists-upstream'.

Once testing of the upstream kernel is complete, please mark this bug as
"Confirmed".


Thanks in advance.

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.3-wily/

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

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

Title:
  Strange kernel or scheduling problem

Status in linux package in Ubuntu:
  Incomplete

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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