sched: Remove get_online_cpus() usage

Remove get_online_cpus() usage from the scheduler; there's 4 sites that
use it:

 - sched_init_smp(); where its completely superfluous since we're in
   'early' boot and there simply cannot be any hotplugging.

 - sched_getaffinity(); we already take a raw spinlock to protect the
   task cpus_allowed mask, this disables preemption and therefore
   also stabilizes cpu_online_mask as that's modified using
   stop_machine. However switch to active mask for symmetry with
   sched_setaffinity()/set_cpus_allowed_ptr(). We guarantee active
   mask stability by inserting sync_rcu/sched() into _cpu_down.

 - sched_setaffinity(); we don't appear to need get_online_cpus()
   either, there's two sites where hotplug appears relevant:
    * cpuset_cpus_allowed(); for the !cpuset case we use possible_mask,
      for the cpuset case we hold task_lock, which is a spinlock and
      thus for mainline disables preemption (might cause pain on RT).
    * set_cpus_allowed_ptr(); Holds all scheduler locks and thus has
      preemption properly disabled; also it already deals with hotplug
      races explicitly where it releases them.

 - migrate_swap(); we can make stop_two_cpus() do the heavy lifting for
   us with a little trickery. By adding a sync_sched/rcu() after the
   CPU_DOWN_PREPARE notifier we can provide preempt/rcu guarantees for
   cpu_active_mask. Use these to validate that both our cpus are active
   when queueing the stop work before we queue the stop_machine works
   for take_cpu_down().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20131011123820.GV3081@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Git-commit: 6acce3ef84520537f8a09a12c9ddbe814a584dd2
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[kaushalk@codeaurora.org: get_online_cpus has only 3 sites of usage in
 kernel/sched/core.c of msm-3.10 so migrate_swap changes are not
 applicable here. stop_two_cpus related change is not applicable to
 msm-3.10, so skip it.]
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>

sched: Remove extra put_online_cpus() inside sched_setaffinity()

Commit 6acce3ef8:

	sched: Remove get_online_cpus() usage

has left one extra put_online_cpus() inside sched_setaffinity(),
remove it to fix the WARN:

   ------------[ cut here ]------------
   WARNING: CPU: 0 PID: 3166 at kernel/cpu.c:84 put_online_cpus+0x43/0x70()
   ...
   [<ffffffff810c3fef>] put_online_cpus+0x43/0x70 [
   [<ffffffff810efd59>] sched_setaffinity+0x7d/0x1f9 [
   ...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/526DD0EE.1090309@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Git-commit: ac9ff7997b6f2b31949dcd2495ac671fd9ddc990
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>

sched: Fix endless sync_sched/rcu() loop inside _cpu_down()

	sched: Remove get_online_cpus() usage

tries to do sync_sched/rcu() inside _cpu_down() but triggers:

	INFO: task swapper/0:1 blocked for more than 120 seconds.
	...
	[<ffffffff811263dc>] synchronize_rcu+0x2c/0x30
	[<ffffffff81d1bd82>] _cpu_down+0x2b2/0x340
	...

It was caused by that in the rcu boost case we rely on smpboot thread to
finish the rcu callback, which has already been parked before sync in here
and leads to the endless sync_sched/rcu().

This patch exchanges the sequence of smpboot_park_threads() and
sync_sched/rcu() to fix the bug.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5282EDC0.6060003@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Git-commit: 106dd5afde3cd10db7e1370b6ddc77f0b2496a75
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>

sched: Remove synchronize rcu/sched calls from _cpu_down

There is no need for sync_sched() in _cpu_down as stop_machine()
provides that barrier implicitly. Removing it also helps improve
hot-unplug latency.
The sync_sched/rcu were earlier removed for the same reason by the
commit 9ee349ad6d326df3633d43f54202427295999c47, but recently got
added as part of commit c4575f83b9fe87bb57b737bc8a667f746a20320a.

Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
arm: atomic.h: defined relaxed atomic_read

Defining relaxed version of atomic read as cpu_relaxed_read_atomic.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: defining relaxed version of idle_cpu

Defining relaxed version of idle_cpu, which uses
macro cpu_relaxed_read_long, that will be used to
enhance power efficiency.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
llist: defining relaxed version of llist_empty

Defining relaxed version of llist_empty as llist_empty_relaxed,
which will be used for power-optimization.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
asm-generic: processor.h: adding new header file

Defining a new header file and adding architecture
independent macros. Using these macros we are optimizing
power usage on ARM64.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
ARM: including asm-generic/processor.h

Here we are including asm-generic/processor.h
because it has defined some generic macros which
can be used by any architecture for optimaztion
of power usage.

bug 1440421

Change-Id: I39db944d348b3dad9235b76d8c7ea3867c0006ce
Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Reviewed-by: Peng Du <pdu@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
seqlock: enhance power efficiency

Trying to improve the power efficiency in linux/seqlock.h,
using macros cpu_relaxed_read and cpu_read_relax.

Bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>