Messages in this thread | | | From | Radim Krčmář <> | Subject | [PATCH v3 0/5] KVM: optimize userspace exits with a new ioctl | Date | Fri, 14 Aug 2015 12:08:32 +0200 |
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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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