trace-cmd-attach - Man Page

trace-cmd attach [Options] host-trace-file guest-trace-file guest-pid [guest-pid ​...]

The trace-cmd(1) attach is used to take a trace​.dat file created on a guest and attach it to a trace​.dat file that was created on the host​. In most cases, trace-cmd-agent(1) can be used to automate this, but if for some reason, the agent isn’t appropriate, it may be required to start trace-cmd recording on the guest with trace-cmd-record(1)​. If the host recording is activated at the same time, one can use trace-cmd attach(1) to connect the guest and host files as if they were created by the trace-cmd agent​.

host-trace-file

The trace​.dat file created by the host​. Must have kvm_exit and kvm_entry events, and use the "tsc2nsec" clock​.

guest-trace-file

The trace​.dat file created by the guest​. Must use the "x86-tsc" clock​. For now, this is only supported on x86, it may support other achitectures later​.

guest-pid

The process ID of the host thread that represents the guests threads​. Each process ID that represents all of the guest vCPUs should be listed​. Note, you can add more than just the threads that represent the guest vCPUs, as the tool will search the host-trace-file for kvm_exit and kvm_entry events to match these PIDs with the vCPUs that they represent​.

-c cpus

Specify a the number of CPUS the guest has​.

-s timeshift

A comma separated list of the format offset,scale,frac,timestamp These values map to what are given in /sys/kernel/kvm/<pid>/vcpu/*

*offset*: Is the offset of the guest​. "tsc-offest" in the directory​. Note
          that the value listed here is the negative of what is listed in
          the directory​.

*scale*:  The scaling factor​. "tsc-scaling-ratio"

*frac*:   The fraction bits​. "tsc-scaling-ratio-frac-bits"

*timestamp*: The timestamp to start using the above​. In some cases, the
          values may change over time​. By adding a timestamp, it will
          take effect after the timestamp has been hit​. Normally
          this would be zero​.

Currently, only one timeshift is given per CPU​. One *-s* option should be
given for each CPU​. If there are less options than CPUs, then the last option
given will be used for the rest of the CPUs​. If only one option is given, then
the values for that option will be used for all CPUs​.

Enable all events for tracing:

  $ # find the process for a given guest
  $ ps aux |grep qemu
 libvirt+   63170  5​.6  1​.6 13994848 4257540 ?    Sl   May02 2884:49 /usr/bin/qemu-system-x86_64​.​.​.

  $ # Use 63170 to find all the PIDs for the give guest
  $ ls /proc/63170/task
 1541591  63170  63198  63209  63211  63213  63214  63215  63216  63217  63218  63219  63234

  $ # Find the tsc offset
  $ su
  # cat /sys/kernel/debug/kvm/63170-15/vcpu0/tsc-offset
 -27950965013436847

  # trace-cmd record -C tsc2nesc -e kvm -e sched -e irq -e timer

# on guest:

  # trace-cmd record -C x86-tsc -e sched -e irq -e timer sleep 10

# back on host, hit Ctrl^C to stop tracing after the guest is done

  # # Make the trace​.dat user owned by your user account​.
  # chown user​.user trace​.dat
  # exit

  $ scp root@guest:trace​.dat trace-guest​.dat

  $ # now attach the two files (guest has 8 CPUs)
  $ trace-cmd attach -c 8 -s 27950965013436847 trace​.dat trace-guest​.dat 1541591  63170  63198  63209  63211  63213  63214  63215  63216  63217  63218  63219  63234

  $ trace-cmd report -i trace​.dat -i trace-guest​.dat
  $ # now you should see the guest trace interleaved within the host trace​.

trace-cmd(1), trace-cmd-report(1), trace-cmd-start(1), trace-cmd-stop(1), trace-cmd-extract(1), trace-cmd-reset(1), trace-cmd-split(1), trace-cmd-list(1), trace-cmd-listen(1), trace-cmd-profile(1)

Written by Steven Rostedt (Google) <rostedt@goodmis​.org​^[1]>

https://git​.kernel​.org/pub/scm/utils/trace-cmd/trace-cmd​.git/

Copyright (C) 2010 Red Hat, Inc​. Free use of this software is granted under the terms of the GNU Public License (GPL)​.

1.

rostedt@goodmis.org
mailto:rostedt@goodmis.org

trace-cmd(1).