trace-cmd-attach(1) — Linux manual page


TRACE-CMD-ATTACH(1)         libtracefs Manual        TRACE-CMD-ATTACH(1)

NAME         top

       trace-cmd-attach - attach a guest trace.dat file to a host
       trace.dat file

SYNOPSIS         top

       trace-cmd attach [OPTIONS] host-trace-file guest-trace-file
       guest-pid [guest-pid ...]

DESCRIPTION         top

       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.

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

           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.

           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.

OPTIONS         top

       -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.

EXAMPLES         top

       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

             # 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.

SEE ALSO         top

       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),

AUTHOR         top

       Written by Steven Rostedt (Google) <[1]>

RESOURCES         top 

COPYING         top

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

NOTES         top


COLOPHON         top

       This page is part of the trace-cmd (a front-end for Ftrace)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this
       manual page, see ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨⟩ on
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-02-22.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

libtracefs                     09/24/2023            TRACE-CMD-ATTACH(1)

Pages that refer to this page: trace-cmd(1)