smp, idle: Allocate idle thread for each possible cpu during boot

percpu areas are already allocated during boot for each possible cpu.
percpu idle threads can be considered as an extension of the percpu areas,
and allocate them for each possible cpu during boot.

This will eliminate the need for workqueue based idle thread allocation.
In future we can move the idle thread area into the percpu area too.

[ tglx: Moved the loop into smpboot.c and added an error check when
  the init code failed to allocate an idle thread for a cpu which
  should be onlined ]

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: venki@google.com
Link: http://lkml.kernel.org/r/1334966930.28674.245.camel@sbsiddha-desk.sc.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
smpboot, idle: Optimize calls to smp_processor_id() in idle_threads_init()

While trying to initialize idle threads for all cpus, idle_threads_init()
calls smp_processor_id() in a loop, which is unnecessary. The intent
is to initialize idle threads for all non-boot cpus. So just use a variable
to note the boot cpu and use it in the loop.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: suresh.b.siddha@intel.com
Cc: venki@google.com
Cc: nikunj@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20120524151055.2549.64309.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
smpboot, idle: Fix comment mismatch over idle_threads_init()

The comment over idle_threads_init() really talks about the functionality
of idle_init(). Move that comment to idle_init(), and add a suitable
comment over idle_threads_init().

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: suresh.b.siddha@intel.com
Cc: venki@google.com
Cc: nikunj@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20120524151100.2549.66501.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>