sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default

The "isolcpus=" boot parameter support was always built-in before we
moved the related code under CONFIG_CPU_ISOLATION. Having it disabled by
default is very confusing for people accustomed to use this parameter.

So enable it by dafault to keep the previous behaviour but keep it
optable for those who want to tinify their kernels.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: kernel test robot <xiaolong.ye@intel.com>
Link: http://lkml.kernel.org/r/1513275507-29200-3-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

init/Kconfig

@@ -461,10 +461,14 @@ endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION
 	bool "CPU isolation"
+	default y
 	help
 	  Make sure that CPUs running critical tasks are not disturbed by
 	  any source of "noise" such as unbound workqueues, timers, kthreads...
-	  Unbound jobs get offloaded to housekeeping CPUs.
+	  Unbound jobs get offloaded to housekeeping CPUs. This is driven by
+	  the "isolcpus=" boot parameter.
+
+	  Say Y if unsure.
 
 source "kernel/rcu/Kconfig"