Public bug reported:
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.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "version_signature"
https://bugs.launchpad.net/bugs/1516565/+attachment/4520050/+files/version.log
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https://bugs.launchpad.net/bugs/1516565
Title:
Strange kernel or scheduling problem
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