[realtime app] disable idle load balancing on cpus from nohz_full= cpuset

[Mykyta Iziumtsev]

We're running realtime application on Ubuntu 16.04 with linux-image 4.15 and found that from time to time we get jitter caused by idle load balancing. I'm providing here a patch which solved the issue for us.

The realtime application is bound to isolated CPUs (one thread per CPU, nohz_full= in kernel cmdline, all IRQs moved to housekeeping CPUs), application doesn't use any linux kernel syscalls except in startup phase so we don't expect any interruptions of the application from the kernel or HW.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1831568

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Tim Gardner (timg-tpi)]

This patch appears to alter the default behavior of a stable kernel in that it essentially disables idle load balancing. Is that a fair assessment ?