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This change has been made by an automated script, maintained by the
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** Changed in: linux (Ubuntu)
Status: New => Incomplete
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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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