linux-kernel - [RFC PATCH 0/3] kvm: x86: speedups for APICv

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Date:   Tue, 27 Sep 2016 23:20:10 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     yang.zhang.wz@...il.com, feng.wu@...el.com, mst@...hat.com,
        rkrcmar@...hat.com
Subject: [RFC PATCH 0/3] kvm: x86: speedups for APICv

These patches save 40 cycles on kvm-unit-tests "inl" tests, but I suspect
the effect is bigger on workloads that inject interrupts heavily.

The difficult one is patch 2.  I find the new code easier to follow than
the old one, but it doesn't mean it works. :)  The aim is for APICv to
not use KVM_REQ_EVENT at all for interrupts, therefore turning APICv's
weakness (having to look at PIR on every vmentry) into a strength
(because checking PIR.ON is cheaper than processing KVM_REQ_EVENT).
The others are just micro-optimization of the surrounding code.

Tested extremely lightly and obviously not for 4.9, just shooting it
out now.

Paolo

Paolo Bonzini (3):
  kvm: x86: avoid atomic operations on APICv vmentry
  kvm: x86: do not use KVM_REQ_EVENT for APICv interrupt injection
  KVM: x86: do not scan IRR twice on APICv vmentry

 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/lapic.c            | 31 +++++++++++++++++++------------
 arch/x86/kvm/lapic.h            |  4 ++--
 arch/x86/kvm/svm.c              |  2 +-
 arch/x86/kvm/vmx.c              | 30 ++++++++++++++++++------------
 arch/x86/kvm/x86.c              | 16 ++++++++++------
 6 files changed, 51 insertions(+), 34 deletions(-)

-- 
1.8.3.1