Provided by: perf-tools-unstable_0.0.1~20150130+git85414b0-1_all bug


       functrace  -  trace kernel function calls matching specified wildcards.
       Uses Linux ftrace.


       functrace [-hH] [-p PID] [-d secs] funcstring


       This tool provides a quick way  to  capture  the  execution  of  kernel
       functions,   showing   basic  details  including  as  the  process  ID,
       timestamp, and calling function.

       WARNING: This uses  dynamic  tracing  of  (what  can  be  many)  kernel
       functions,  and  could  cause  kernel panics or freezes. Test, and know
       what you are doing, before use.

       Also beware of feedback loops:  tracing  tcp*  functions  over  an  ssh
       session,  or  writing  ext4*  functions to an ext4 file system. For the
       former, tcp trace data could be redirected to a file (as in  the  usage
       message).  For  the  latter,  trace  to  the screen or a different file

       SEE ALSO: kprobe(8), which can dynamically trace a single function call
       or return, and examine CPU registers and return values.

       Since this uses ftrace, only the root user can use this tool.


       FTRACE  CONFIG,  which  you  may  already have enabled and available on
       recent kernels.


       -d seconds
              Set the duration of tracing, in seconds. Trace  output  will  be
              buffered  and printed at the end. This also reduces overheads by
              buffering in-kernel, instead of printing events as they occur.

              The   ftrace   buffer   has   a   fixed   size   per-CPU    (see
              /sys/kernel/debug/tracing/buffer_size_kb).  If  you think events
              are missing, try increasing that size.

       -h     Print usage message.

       -H     Print column headers.

       -p PID Only trace kernel functions when this process ID is on-CPU.

              A function name to trace, which  may  include  file  glob  style
              wildcards ("*") at the beginning or ending of a string only. Eg,
              "vfs*" means match "vfs" followed by anything.


       Trace calls to do_nanosleep():
              # functrace do_nanosleep

       Trace calls to all kernel functions ending in "*sleep":
              # functrace '*sleep'

       Trace all "vfs*" kernel function calls for PID 198:
              # functrace -p 198 'vfs*'

       Trace all "tcp*" kernel function calls, and  output  to  a  file  until
              # functrace 'tcp*' > out

       Trace  all "tcp*" kernel function calls, output to a file, for 1 second
              # functrace -d 1 'tcp*' > out


       The output format depends on the kernel version, and  headings  can  be
       printed  using  -H. The format is the same as the ftrace function trace
       format,     described     in     the      kernel      source      under

       Typical fields are:

              The  process  name (which could include dashes), a dash, and the
              process ID.

       CPU#   The CPU ID, in brackets.

       ||||   Kernel state flags. For example, on Linux  3.16  these  are  for
              irqs-off, need-resched, hardirq/softirq, and preempt-depth.

              Time of event, in seconds.

              Kernel function name.


       This  can  generate  a  lot  of  trace  data  quickly, depending on the
       frequency of the  traced  events.  Such  data  will  cause  performance
       overheads.   This  also  works  without  buffering by default, printing
       function events as they happen (uses trace_pipe), context switching and
       consuming  CPU  to  do so. If needed, you can try the "-d secs" option,
       which buffers events instead,  reducing  overhead.  If  you  think  the
       buffer  option  is  losing  events,  try  increasing  the  buffer  size

       It's a good idea to use funccount(8) first, which is lower overhead, to
       help   you   select  which  functions  you  may  want  to  trace  using


       This is from the perf-tools collection:


       Also look under the examples  directory  for  a  text  file  containing
       example usage, output, and commentary for this tool.




       Unstable - in development.


       Brendan Gregg


       funccount(8), kprobe(8)