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| author | Wanpeng Li <wanpengli@tencent.com> | 2019-11-21 11:17:11 +0800 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-01-21 13:57:12 +0100 |
| commit | 1e9e2622a149e88bd636c9f8fb346a6e6aefeae0 (patch) | |
| tree | 37cc18df956d3bea2ade77396f9e79138d3c3b3d /arch/x86/kvm/svm.c | |
| parent | 6948199a9af969342a6faf257678616aea491fcf (diff) | |
| download | lwn-1e9e2622a149e88bd636c9f8fb346a6e6aefeae0.tar.gz lwn-1e9e2622a149e88bd636c9f8fb346a6e6aefeae0.zip | |
KVM: VMX: FIXED+PHYSICAL mode single target IPI fastpath
ICR and TSCDEADLINE MSRs write cause the main MSRs write vmexits in our
product observation, multicast IPIs are not as common as unicast IPI like
RESCHEDULE_VECTOR and CALL_FUNCTION_SINGLE_VECTOR etc.
This patch introduce a mechanism to handle certain performance-critical
WRMSRs in a very early stage of KVM VMExit handler.
This mechanism is specifically used for accelerating writes to x2APIC ICR
that attempt to send a virtual IPI with physical destination-mode, fixed
delivery-mode and single target. Which was found as one of the main causes
of VMExits for Linux workloads.
The reason this mechanism significantly reduce the latency of such virtual
IPIs is by sending the physical IPI to the target vCPU in a very early stage
of KVM VMExit handler, before host interrupts are enabled and before expensive
operations such as reacquiring KVM’s SRCU lock.
Latency is reduced even more when KVM is able to use APICv posted-interrupt
mechanism (which allows to deliver the virtual IPI directly to target vCPU
without the need to kick it to host).
Testing on Xeon Skylake server:
The virtual IPI latency from sender send to receiver receive reduces
more than 200+ cpu cycles.
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/svm.c')
| -rw-r--r-- | arch/x86/kvm/svm.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 8f1b715dfde8..9583ae7ae218 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -4935,7 +4935,8 @@ static void svm_get_exit_info(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2) *info2 = control->exit_info_2; } -static int handle_exit(struct kvm_vcpu *vcpu) +static int handle_exit(struct kvm_vcpu *vcpu, + enum exit_fastpath_completion exit_fastpath) { struct vcpu_svm *svm = to_svm(vcpu); struct kvm_run *kvm_run = vcpu->run; @@ -4993,7 +4994,10 @@ static int handle_exit(struct kvm_vcpu *vcpu) __func__, svm->vmcb->control.exit_int_info, exit_code); - if (exit_code >= ARRAY_SIZE(svm_exit_handlers) + if (exit_fastpath == EXIT_FASTPATH_SKIP_EMUL_INS) { + kvm_skip_emulated_instruction(vcpu); + return 1; + } else if (exit_code >= ARRAY_SIZE(svm_exit_handlers) || !svm_exit_handlers[exit_code]) { vcpu_unimpl(vcpu, "svm: unexpected exit reason 0x%x\n", exit_code); dump_vmcb(vcpu); @@ -6186,9 +6190,12 @@ out: return ret; } -static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu) +static void svm_handle_exit_irqoff(struct kvm_vcpu *vcpu, + enum exit_fastpath_completion *exit_fastpath) { - + if (!is_guest_mode(vcpu) && + to_svm(vcpu)->vmcb->control.exit_code == EXIT_REASON_MSR_WRITE) + *exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu); } static void svm_sched_in(struct kvm_vcpu *vcpu, int cpu) |