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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. Cc: Peter Zijlstra <peterz@infradead.org> Cc: Clark Williams <williams@redhat.com> Cc: Li Zefan <lizefan@huawei.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: cgroups@vger.kernel.org Signed-off-by: Rik van Riel <riel@redhat.com> Tested-by: David Rientjes <rientjes@google.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Zefan Li <lizefan@huawei.com> Signed-off-by: Tejun Heo <tj@kernel.org>