linux-kernel - [PATCH v3 0/5] KVM: optimize userspace exits with a new ioctl

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Date:	Fri, 14 Aug 2015 12:08:32 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH v3 0/5] KVM: optimize userspace exits with a new ioctl

v3:
 * acked by Christian [1/5]
 * use ioctl argument directly (unsigned long as flags) [4/5]
 * precisely #ifdef arch-specific ioctls [5/5]
v2:
 * move request_exits debug counter patch right after introduction of
   KVM_REQ_EXIT [3/5]
 * use vcpu ioctl instead of vm one [4/5]
 * shrink kvm_user_exit from 64 to 32 bytes [4/5]
 * new [5/5]

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: x86: add request_exits debug counter
  KVM: add KVM_USER_EXIT vcpu ioctl for userspace exit
  KVM: refactor asynchronous vcpu ioctl dispatch

 Documentation/virtual/kvm/api.txt | 25 +++++++++++++++++++++++++
 arch/x86/include/asm/kvm_host.h   |  1 +
 arch/x86/kvm/vmx.c                |  4 ++--
 arch/x86/kvm/x86.c                | 23 +++++++++++++++++++++++
 include/linux/kvm_host.h          | 15 +++++++++++++--
 include/uapi/linux/kvm.h          |  4 ++++
 virt/kvm/kvm_main.c               | 15 ++++++++++-----
 7 files changed, 78 insertions(+), 9 deletions(-)

-- 
2.5.0

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