linux-kernel - [PATCH 0/5] KVM: optimize userspace exits with a new ioctl

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Message-Id: <1438780877-31838-1-git-send-email-rkrcmar@redhat.com>
Date:	Wed,  5 Aug 2015 15:21:12 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 0/5] KVM: optimize userspace exits with a new ioctl

QEMU uses SIGUSR1 to force a userspace exit and also to queue an early
exit before calling VCPU_RUN -- the signal is blocked in user space and
temporarily unblocked in VCPU_RUN.
The temporal unblocking by sigprocmask() in kvm_arch_vcpu_ioctl_run()
takes a shared siglock, which leads to cacheline bouncing in NUMA
systems.

This series allows the same with a new request bit and VM IOCTL that
marks and kicks target VCPU, hence no need to unblock.

inl_from_{pmtimer,qemu} vmexit benchmark from kvm-unit-tests shows ~5%
speedup for 1-4 VCPUs (300-2000 saved cycles) without noticeably
regressing kernel VM exits.
(Paolo did a quick run of older version of this series on a NUMA system
 and the speedup was around 35% when utilizing more nodes.)

Radim Krčmář (5):
  KVM: add kvm_has_request wrapper
  KVM: add KVM_REQ_EXIT request for userspace exit
  KVM: add KVM_USER_EXIT vm ioctl for userspace exit
  KVM: optimize common cases in KVM_USER_EXIT
  KVM: x86: add request_exits debug counter

 Documentation/virtual/kvm/api.txt | 30 ++++++++++++++++++++++++++++
 arch/x86/include/asm/kvm_host.h   |  1 +
 arch/x86/kvm/vmx.c                |  4 ++--
 arch/x86/kvm/x86.c                |  9 +++++++++
 include/linux/kvm_host.h          | 15 ++++++++++++--
 include/uapi/linux/kvm.h          |  9 +++++++++
 virt/kvm/kvm_main.c               | 41 ++++++++++++++++++++++++++++++++++++++-
 7 files changed, 104 insertions(+), 5 deletions(-)

-- 
2.5.0

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