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perf intel-pt: Add documentation for tracing virtual machines
Add documentation to the perf-intel-pt man page for tracing virtual machines. Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Acked-by: Andi Kleen <ak@linux.intel.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Link: https://lore.kernel.org/r/20210218095801.19576-12-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Adrian Hunter
Arnaldo Carvalho de Melo
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1 changed files with 82 additions and 0 deletions
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@ -1146,6 +1146,88 @@ XED
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include::build-xed.txt[]
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Tracing Virtual Machines
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------------------------
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Currently, only kernel tracing is supported and only with "timeless" decoding
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i.e. no TSC timestamps
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Other limitations and caveats
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VMX controls may suppress packets needed for decoding resulting in decoding errors
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VMX controls may block the perf NMI to the host potentially resulting in lost trace data
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Guest kernel self-modifying code (e.g. jump labels or JIT-compiled eBPF) will result in decoding errors
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Guest thread information is unknown
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Guest VCPU is unknown but may be able to be inferred from the host thread
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Callchains are not supported
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Example
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Start VM
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$ sudo virsh start kubuntu20.04
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Domain kubuntu20.04 started
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Mount the guest file system. Note sshfs needs -o direct_io to enable reading of proc files. root access is needed to read /proc/kcore.
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$ mkdir vm0
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$ sshfs -o direct_io root@vm0:/ vm0
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Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore
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$ perf buildid-cache -v --kcore vm0/proc/kcore
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kcore added to build-id cache directory /home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306
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$ KALLSYMS=/home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306/kallsyms
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Find the VM process
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$ ps -eLl | grep 'KVM\|PID'
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F S UID PID PPID LWP C PRI NI ADDR SZ WCHAN TTY TIME CMD
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3 S 64055 1430 1 1440 1 80 0 - 1921718 - ? 00:02:47 CPU 0/KVM
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3 S 64055 1430 1 1441 1 80 0 - 1921718 - ? 00:02:41 CPU 1/KVM
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3 S 64055 1430 1 1442 1 80 0 - 1921718 - ? 00:02:38 CPU 2/KVM
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3 S 64055 1430 1 1443 2 80 0 - 1921718 - ? 00:03:18 CPU 3/KVM
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Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
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TSC is not supported and tsc=0 must be specified. That means mtc is useless, so add mtc=0.
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However, IPC can still be determined, hence cyc=1 can be added.
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Only kernel decoding is supported, so 'k' must be specified.
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Intel PT traces both the host and the guest so --guest and --host need to be specified.
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Without timestamps, --per-thread must be specified to distinguish threads.
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$ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/tsc=0,mtc=0,cyc=1/k -p 1430 --per-thread
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^C
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[ perf record: Woken up 1 times to write data ]
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[ perf record: Captured and wrote 5.829 MB ]
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perf script can be used to provide an instruction trace
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$ perf script --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
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CPU 0/KVM 1440 ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms]) movq 0x48(%rax), %r9
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CPU 0/KVM 1440 ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms]) movq 0x50(%rax), %r10
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CPU 0/KVM 1440 ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms]) movq 0x58(%rax), %r11
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CPU 0/KVM 1440 ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms]) movq 0x60(%rax), %r12
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CPU 0/KVM 1440 ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms]) movq 0x68(%rax), %r13
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CPU 0/KVM 1440 ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms]) movq 0x70(%rax), %r14
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CPU 0/KVM 1440 ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms]) movq 0x78(%rax), %r15
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CPU 0/KVM 1440 ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms]) movq (%rax), %rax
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CPU 0/KVM 1440 ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms]) callq 0xffffffff82133c40
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CPU 0/KVM 1440 ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms]) jz 0xffffffff82133c46
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CPU 0/KVM 1440 ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms]) vmresume IPC: 0.11 (50/445)
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:1440 1440 ffffffffbb678b06 native_write_msr+0x6 ([guest.kernel.kallsyms]) nopl %eax, (%rax,%rax,1)
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:1440 1440 ffffffffbb678b0b native_write_msr+0xb ([guest.kernel.kallsyms]) retq IPC: 0.04 (2/41)
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:1440 1440 ffffffffbb666646 lapic_next_deadline+0x26 ([guest.kernel.kallsyms]) data16 nop
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:1440 1440 ffffffffbb666648 lapic_next_deadline+0x28 ([guest.kernel.kallsyms]) xor %eax, %eax
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:1440 1440 ffffffffbb66664a lapic_next_deadline+0x2a ([guest.kernel.kallsyms]) popq %rbp
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:1440 1440 ffffffffbb66664b lapic_next_deadline+0x2b ([guest.kernel.kallsyms]) retq IPC: 0.16 (4/25)
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:1440 1440 ffffffffbb74607f clockevents_program_event+0x8f ([guest.kernel.kallsyms]) test %eax, %eax
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:1440 1440 ffffffffbb746081 clockevents_program_event+0x91 ([guest.kernel.kallsyms]) jz 0xffffffffbb74603c IPC: 0.06 (2/30)
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:1440 1440 ffffffffbb74603c clockevents_program_event+0x4c ([guest.kernel.kallsyms]) popq %rbx
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:1440 1440 ffffffffbb74603d clockevents_program_event+0x4d ([guest.kernel.kallsyms]) popq %r12
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SEE ALSO
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--------
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