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

Radim Krčmář
2015-08-14T10:11:34Z

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(-)

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2.5.0