[PATCH v4 RESEND 0/4] cpusets,isolcpus: exclude isolcpus from load balancing in cpusets

[riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org]

Ensure that cpus specified with the isolcpus= boot commandline
option stay outside of the load balancing in the kernel scheduler.

Operations like load balancing can introduce unwanted latencies,
which is exactly what the isolcpus= commandline is there to prevent.

Previously, simply creating a new cpuset, without even touching the
cpuset.cpus field inside the new cpuset, would undo the effects of
isolcpus=, by creating a scheduler domain spanning the whole system,
and setting up load balancing inside that domain. The cpuset root
cpuset.cpus file is read-only, so there was not even a way to undo
that effect.

This does not impact the majority of cpusets users, since isolcpus=
is a fairly specialized feature used for realtime purposes.

This version fixes the UP compilation issue, in the same way done
for the other cpumasks.