2.2. perf kvm

Procedure 2.1. Copying /proc files from guest to host

1. Log in to the guest and save files

   Log in to the guest and save /proc/modules and /proc/kallsyms to a temporary location, /tmp:

   # cat /proc/modules > /tmp/modules
   # cat /proc/kallsyms > /tmp/kallsyms
   

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2. Copy the temporary files to the host

   Once you have logged off from the guest, run the following example scp commands to copy the saved files to the host. You should substitute your host name and TCP port if they are different:

   # scp root@GuestMachine:/tmp/kallsyms guest-kallsyms
   # scp root@GuestMachine:/tmp/modules guest-modules
   

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   You now have two files from the guest (guest-kallsyms and guest-modules) on the host, ready for use by perf kvm.

3. Recording and reporting events with perf kvm

   Using the files obtained in the previous steps, recording and reporting of events in the guest, the host, or both is now possible.
   Run the following example command:

   # perf kvm --host --guest --guestkallsyms=guest-kallsyms \
   --guestmodules=guest-modules record -a -o perf.data
   

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   Note

   If both --host and --guest are used in the command, output will be stored in perf.data.kvm. If only --host is used, the file will be named perf.data.host. Similarly, if only --guest is used, the file will be named perf.data.guest.
   Pressing Ctrl-C stops recording.

4. Reporting events

   The following example command uses the file obtained by the recording process, and redirects the output into a new file, analyze.

   perf kvm --host --guest --guestmodules=guest-modules report -i perf.data.kvm \
   --force > analyze
   

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   View the contents of the analyze file to examine the recorded events:

   # cat analyze
   
   
   # Events: 7K cycles
   #
   # Overhead       Command  Shared Object      Symbol
   # ........  ............  .................  .........................
   #
       95.06%            vi  vi                 [.] 0x48287
        0.61%          init  [kernel.kallsyms]  [k] intel_idle
        0.36%            vi  libc-2.12.so       [.] _wordcopy_fwd_aligned
        0.32%            vi  libc-2.12.so       [.] __strlen_sse42
        0.14%       swapper  [kernel.kallsyms]  [k] intel_idle
        0.13%          init  [kernel.kallsyms]  [k] uhci_irq
        0.11%          perf  [kernel.kallsyms]  [k] generic_exec_single
        0.11%          init  [kernel.kallsyms]  [k] tg_shares_up
        0.10%      qemu-kvm  [kernel.kallsyms]  [k] tg_shares_up
   
   [output truncated...]
   

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Procedure 2.2. Alternative: using sshfs to directly access files

• Important

  This is provided as an example only. You will need to substitute values according to your environment.

  # Get the PID of the qemu process for the guest:
  PID=`ps -eo pid,cmd | grep "qemu.*-name GuestMachine" \
  | grep -v grep | awk '{print $1}'`
  
  # Create mount point and mount guest
  mkdir -p /tmp/guestmount/$PID
  sshfs -o allow_other,direct_io GuestMachine:/ /tmp/guestmount/$PID
  
  # Begin recording
  perf kvm --host --guest --guestmount=/tmp/guestmount \
  record -a -o perf.data
  
  # Ctrl-C interrupts recording. Run report:
  perf kvm --host --guest --guestmount=/tmp/guestmount report \
  -i perf.data
  
  # Unmount sshfs to the guest once finished:
  fusermount -u /tmp/guestmount
  

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