[PATCH v3] Enable haltpoll for arm64

[Mihai Carabas]

This patchset enables the usage of haltpoll governer on arm64. This is
specifically interesting for KVM guests by reducing the IPC latencies.

Here are some benchmarks without/with haltpoll for a KVM guest:

a) without haltpoll:
perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes

     Total time: 8.138 [sec]

            8.138094 usecs/op
             122878 ops/sec

b) with haltpoll:
perf bench sched pipe
# Running 'sched/pipe' benchmark:
# Executed 1000000 pipe operations between two processes

     Total time: 5.003 [sec]

            5.003085 usecs/op
             199876 ops/sec

v3 changes from v2:
- fix 1/7 per Petr Mladek - remove ARCH_HAS_CPU_RELAX from arch/x86/Kconfig
- add Ack-by from Rafael Wysocki on 2/7

v2 changes from v1:
- added patch 7 where we change cpu_relax with smp_cond_load_relaxed per PeterZ
  (this improves by 50% at least the CPU cycles consumed in the tests above:
  10,716,881,137 now vs 14,503,014,257 before)
- removed the ifdef from patch 1 per RafaelW

Joao Martins (6):
  x86: Move ARCH_HAS_CPU_RELAX to arch
  x86/kvm: Move haltpoll_want() to be arch defined
  governors/haltpoll: Drop kvm_para_available() check
  arm64: Select ARCH_HAS_CPU_RELAX
  arm64: Define TIF_POLLING_NRFLAG
  cpuidle-haltpoll: ARM64 support

Mihai Carabas (1):
  cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed

 arch/Kconfig                            |  3 +++
 arch/arm64/Kconfig                      |  1 +
 arch/arm64/include/asm/thread_info.h    |  6 ++++++
 arch/x86/Kconfig                        |  4 +---
 arch/x86/include/asm/cpuidle_haltpoll.h |  1 +
 arch/x86/kernel/kvm.c                   | 10 ++++++++++
 drivers/cpuidle/Kconfig                 |  4 ++--
 drivers/cpuidle/cpuidle-haltpoll.c      |  8 ++------
 drivers/cpuidle/governors/haltpoll.c    |  5 +----
 drivers/cpuidle/poll_state.c            | 14 +++++++++-----
 include/linux/cpuidle_haltpoll.h        |  5 +++++
 11 files changed, 41 insertions(+), 20 deletions(-)

-- 
1.8.3.1