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

Radim Krčmář
2015-08-05T13:21:12Z

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(-)

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2.5.0