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From:   Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To:     Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>
Cc:     suleiman@google.com, joelaf@google.com,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: [RFC][PATCH 0/4] arm64:kvm: teach guest sched that VCPUs can be preempted
Date:   Tue, 21 Jul 2020 13:17:38 +0900
Message-Id: <20200721041742.197354-1-sergey.senozhatsky@gmail.com>
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Hello,

	RFC

	We noticed that in a number of cases when we wake_up_process()
on arm64 guest we end up enqueuing that task on a preempted VCPU. The culprit
appears to be the fact that arm64 guests are not aware of VCPU preemption
as such, so when sched picks up an idle VCPU it always assumes that VCPU
is available:

      wake_up_process()
       try_to_wake_up()
        select_task_rq_fair()
         available_idle_cpu()
          vcpu_is_preempted()    // return false;

Which is, obviously, not the case.

This RFC patch set adds a simple vcpu_is_preempted() implementation so
that scheduler can make better decisions when it search for the idle
(v)CPU.

I ran a number of sched benchmarks please refer to [0] for more
details.

[0] https://github.com/sergey-senozhatsky/arm64-vcpu_is_preempted

Sergey Senozhatsky (4):
  arm64:kvm: define pv_state SMCCC HV calls
  arm64: add guest pvstate support
  arm64: add host pvstate support
  arm64: do not use dummy vcpu_is_preempted() anymore

 arch/arm64/include/asm/kvm_host.h  |  23 ++++++
 arch/arm64/include/asm/paravirt.h  |  15 ++++
 arch/arm64/include/asm/spinlock.h  |  17 +++--
 arch/arm64/kernel/Makefile         |   2 +-
 arch/arm64/kernel/paravirt-state.c | 117 +++++++++++++++++++++++++++++
 arch/arm64/kernel/paravirt.c       |   4 +-
 arch/arm64/kernel/time.c           |   1 +
 arch/arm64/kvm/Makefile            |   2 +-
 arch/arm64/kvm/arm.c               |   4 +
 arch/arm64/kvm/hypercalls.c        |  11 +++
 arch/arm64/kvm/pvstate.c           |  58 ++++++++++++++
 include/linux/arm-smccc.h          |  18 +++++
 12 files changed, 262 insertions(+), 10 deletions(-)
 create mode 100644 arch/arm64/kernel/paravirt-state.c
 create mode 100644 arch/arm64/kvm/pvstate.c

-- 
2.27.0