linux-kernel - [PATCH v3] Enable haltpoll for arm64

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Date: Mon, 29 Jan 2024 12:40:27 +0200
From: Mihai Carabas <mihai.carabas@...cle.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: kvm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, catalin.marinas@....com, will@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, pbonzini@...hat.com, wanpengli@...cent.com,
        vkuznets@...hat.com, rafael@...nel.org, daniel.lezcano@...aro.org,
        akpm@...ux-foundation.org, pmladek@...e.com, peterz@...radead.org,
        dianders@...omium.org, npiggin@...il.com, rick.p.edgecombe@...el.com,
        joao.m.martins@...cle.com, juerg.haefliger@...onical.com,
        mic@...ikod.net, mihai.carabas@...cle.com, arnd@...db.de,
        ankur.a.arora@...cle.com
Subject: [PATCH v3] Enable haltpoll for arm64

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