Perf events

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This page describes how to count and trace performance events in the KVM kernel module.

There are two tools, kvm_stat and kvm_trace, which were previously used for these tasks. Now this can be done using standard Linux tracing tools.

Counting events

Often you want event counts after running a benchmark:

$ sudo mount -t debugfs none /sys/kernel/debug
$ sudo ./perf stat -e 'kvm:*' -a sleep 1h
^C
 Performance counter stats for 'sleep 1h':

           8330  kvm:kvm_entry            #      0.000 M/sec
              0  kvm:kvm_hypercall        #      0.000 M/sec
           4060  kvm:kvm_pio              #      0.000 M/sec
              0  kvm:kvm_cpuid            #      0.000 M/sec
           2681  kvm:kvm_apic             #      0.000 M/sec
           8343  kvm:kvm_exit             #      0.000 M/sec
            737  kvm:kvm_inj_virq         #      0.000 M/sec
              0  kvm:kvm_page_fault       #      0.000 M/sec
              0  kvm:kvm_msr              #      0.000 M/sec
            664  kvm:kvm_cr               #      0.000 M/sec
            872  kvm:kvm_pic_set_irq      #      0.000 M/sec
              0  kvm:kvm_apic_ipi         #      0.000 M/sec
            738  kvm:kvm_apic_accept_irq  #      0.000 M/sec
            874  kvm:kvm_set_irq          #      0.000 M/sec
            874  kvm:kvm_ioapic_set_irq   #      0.000 M/sec
              0  kvm:kvm_msi_set_irq      #      0.000 M/sec
            433  kvm:kvm_ack_irq          #      0.000 M/sec
           2685  kvm:kvm_mmio             #      0.000 M/sec

    3.493562100  seconds time elapsed

The perf tool is part of the Linux kernel tree in tools/perf.

Tracing events

Detailed traces can be generated using ftrace:

# mount -t debugfs none /sys/kernel/debug
# echo 1 >/sys/kernel/debug/tracing/events/kvm/enable
# cat /sys/kernel/debug/tracing/trace_pipe
[...]
             kvm-5664  [000] 11906.220178: kvm_entry: vcpu 0
             kvm-5664  [000] 11906.220181: kvm_exit: reason apic_access rip 0xc011518c
             kvm-5664  [000] 11906.220183: kvm_mmio: mmio write len 4 gpa 0xfee000b0 val 0x0
             kvm-5664  [000] 11906.220183: kvm_apic: apic_write APIC_EOI = 0x0
             kvm-5664  [000] 11906.220184: kvm_ack_irq: irqchip IOAPIC pin 11
             kvm-5664  [000] 11906.220185: kvm_entry: vcpu 0
             kvm-5664  [000] 11906.220188: kvm_exit: reason io_instruction rip 0xc01e4473
             kvm-5664  [000] 11906.220188: kvm_pio: pio_read at 0xc13e size 2 count 1
             kvm-5664  [000] 11906.220193: kvm_entry: vcpu 0
^D
# echo 0 >/sys/kernel/debug/tracing/events/kvm/enable

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