Linux kvm_stat VCPU Statistics and perf_event Integration

Linux kvm_stat VCPU Statistics and perf_event Integrationkvm_stat是KVM的性能统计基础设施用于暴露VCPU级别的虚拟化事件计数。它通过tracepoint、debugfs和perf_event三种路径收集数据。内核侧的实现集中在virt/kvm/kvm_main.c和arch/x86/kvm/的统计计数器更新点用户侧通过tools/kvm/kvm_stat/kvm_stat脚本解析并展示。内核侧VCPU统计定义在struct kvm_vcpu_stat和struct kvm_vm_stat中cstruct kvm_vcpu_stat {u64 halt_successful_poll;u64 halt_attempted_poll;u64 halt_poll_invalid;u64 halt_wakeup;u64 hypercalls;u64 req_event;u64 irq_injections;u64 irq_window_exits;u64 nmi_window_exits;u64 signal_exits;u64 pf_fixed;u64 pf_guest;u64 tlb_flush;u64 invlpg;u64 io_exits;u64 mmio_exits;u64 cpuid_exits;u64 halt_exits;u64 irq_exits;u64 host_state_reload;u64 fpu_reload;u64 insn_emulation;u64 insn_emulation_fail;u64 nmi_injections;};struct kvm_vm_stat {u64 mmu_shadow_zapped;u64 mmu_pte_write;u64 mmu_pde_zapped;u64 mmu_flooded;u64 mmu_recycled;u64 mmu_cache_miss;u64 mmu_unsync;u64 remote_tlb_flush;u64 lpages;u64 max_mmu_page_hash_collisions;};统计计数更新在代码各关键路径通过this_cpu_inc或atomic64_inc触发c/* KVM_RUN路径中统计中断注入次数 */static void kvm_inject_irq(struct kvm_vcpu *vcpu){vcpu-stat.irq_injections;/* 实际注入中断到虚拟IRQ chip */kvm_x86_ops.set_irq(vcpu);/* 如果使用perf_event上报触发采样 */if (vcpu-kvm-arch.perf_caps KVM_PERF_CAP_IRQ_INJECT)perf_event_do_callchain(vcpu);}/* 缺页处理路径统计 */static int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code){int r;if (error_code PFERR_GUEST_MASK)vcpu-stat.pf_guest;elsevcpu-stat.pf_fixed;r vcpu-arch.mmu-page_fault(vcpu, gpa, error_code);if (r 0)goto out;return r;out:return r;}/* VM-Exit原因分发统计 */static int vcpu_enter_guest(struct kvm_vcpu *vcpu){/* ... */switch (exit_reason) {case EXIT_REASON_IO_INSTRUCTION:vcpu-stat.io_exits;break;case EXIT_REASON_MSR_READ:case EXIT_REASON_MSR_WRITE:vcpu-stat.msr_exits;break;case EXIT_REASON_CPUID:vcpu-stat.cpuid_exits;break;case EXIT_REASON_HLT:vcpu-stat.halt_exits;break;case EXIT_REASON_EPT_VIOLATION:vcpu-stat.mmio_exits;break;/* ... */}}perf_event集成通过KVM的perf子系统实现KVM注册perf callbacks使得perf工具能够采样VCPU执行时的PMU事件c/* KVM perf_event注册接口 */int kvm_perf_register(struct kvm *kvm){int ret;/* 注册perf回调 */kvm-arch.perf_caps KVM_PERF_CAP_PMU | KVM_PERF_CAP_TRACE;/* 创建perf_event上下文 */ret perf_event_create_kernel_counter(kvm-arch.perf_attr,-1, current-pid,kvm_perf_event_handler,kvm);if (ret 0)return ret;/* 注册VCPU层面的perf_event */kvm_for_each_vcpu(i, vcpu, kvm) {vcpu-arch.perf_event perf_event_create_kernel_counter(vcpu-arch.perf_attr, -1, vcpu-pid,kvm_vcpu_perf_event_handler, vcpu);}return 0;}/* perf_event采样回调记录Guest IP */static void kvm_vcpu_perf_event_handler(struct perf_event *event,struct perf_sample_data *data,struct pt_regs *regs){struct kvm_vcpu *vcpu event-private;struct pt_regs guest_regs;/* 保存Guest RIP信息到perf sample */kvm_get_guest_regs(vcpu, guest_regs);/* 标记为Guest模式采样 */data-sample_flags | PERF_SAMPLE_GUEST;data-guest_ip guest_regs.ip;data-guest_kernel !(vcpu-arch.cr0 X86_CR0_PE) ||guest_regs.cs 3;perf_sample_output(event, data, guest_regs);}kvm_stat用户态工具通过以下三种数据源聚合统计信息debugfs读取/sys/kernel/debug/kvm/*/stat/下的各统计文件tracepoint通过perf_event_open挂载kvm:kvm_entry/kvm:kvm_exit等tracepoint事件perf_event直接读取PMU计数器。kvm_stat命令默认使用debugfs模式每隔指定间隔刷新显示kvm_stat -lEvent Total% Cur%pf_fixed 12.34 15.21io_exits 8.76 9.45irq_injections 7.89 8.12mmio_exits 6.54 7.01halt_exits 5.43 5.67cpuid_exits 4.21 4.89signal_exits 3.12 2.98VCPU统计在KVM内部通过struct kvm_stat_data封装关联到对应的stat字段和perf_event文件描述符。统计值通过kvm_stat_data_read导出到debugfs用户态读文件即触发stat_fops.read回调返回当前累加值。perf_event集成使得kvm_stat可以同时展示Host和Guest的PMU计数用于分析VT-x/AMD-V的exit频率分布、EPT miss比率、中断注入延迟等关键性能指标。