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KVM: Boost vCPU candidate in user mode which is delivering interrupt
Both lock holder vCPU and IPI receiver that has halted are condidate for boost. However, the PLE handler was originally designed to deal with the lock holder preemption problem. The Intel PLE occurs when the spinlock waiter is in kernel mode. This assumption doesn't hold for IPI receiver, they can be in either kernel or user mode. the vCPU candidate in user mode will not be boosted even if they should respond to IPIs. Some benchmarks like pbzip2, swaptions etc do the TLB shootdown in kernel mode and most of the time they are running in user mode. It can lead to a large number of continuous PLE events because the IPI sender causes PLE events repeatedly until the receiver is scheduled while the receiver is not candidate for a boost. This patch boosts the vCPU candidiate in user mode which is delivery interrupt. We can observe the speed of pbzip2 improves 10% in 96 vCPUs VM in over-subscribe scenario (The host machine is 2 socket, 48 cores, 96 HTs Intel CLX box). There is no performance regression for other benchmarks like Unixbench spawn (most of the time contend read/write lock in kernel mode), ebizzy (most of the time contend read/write sem and TLB shoodtdown in kernel mode). Signed-off-by: Wanpeng Li <wanpengli@tencent.com> Message-Id: <1618542490-14756-1-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -11093,6 +11093,14 @@ bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu)
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return false;
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}
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bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
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{
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if (vcpu->arch.apicv_active && static_call(kvm_x86_dy_apicv_has_pending_interrupt)(vcpu))
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return true;
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return false;
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}
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bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
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{
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return vcpu->arch.preempted_in_kernel;
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@ -960,6 +960,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
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bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu);
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int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
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bool kvm_arch_dy_runnable(struct kvm_vcpu *vcpu);
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bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
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int kvm_arch_post_init_vm(struct kvm *kvm);
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void kvm_arch_pre_destroy_vm(struct kvm *kvm);
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@ -3137,6 +3137,11 @@ static bool vcpu_dy_runnable(struct kvm_vcpu *vcpu)
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return false;
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}
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bool __weak kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu)
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{
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return false;
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}
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void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
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{
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struct kvm *kvm = me->kvm;
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@ -3170,7 +3175,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
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!vcpu_dy_runnable(vcpu))
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continue;
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if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
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!kvm_arch_vcpu_in_kernel(vcpu))
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!kvm_arch_dy_has_pending_interrupt(vcpu) &&
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!kvm_arch_vcpu_in_kernel(vcpu))
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continue;
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if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
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continue;
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