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PERF-SCRIPT-PYTHON(1)             perf Manual            PERF-SCRIPT-PYTHON(1)



NAME
       perf-script-python - Process trace data with a Python script

SYNOPSIS
       perf script [-s [Python]:script[.py] ]

DESCRIPTION
       This perf script option is used to process perf script data using perf's built-in Python interpreter. It reads
       and processes the input file and displays the results of the trace analysis implemented in the given Python
       script, if any.

A QUICK EXAMPLE
       This section shows the process, start to finish, of creating a working Python script that aggregates and
       extracts useful information from a raw perf script stream. You can avoid reading the rest of this document if
       an example is enough for you; the rest of the document provides more details on each step and lists the library
       functions available to script writers.

       This example actually details the steps that were used to create the syscall-counts script you see when you
       list the available perf script scripts via perf script -l. As such, this script also shows how to integrate
       your script into the list of general-purpose perf script scripts listed by that command.

       The syscall-counts script is a simple script, but demonstrates all the basic ideas necessary to create a useful
       script. Here's an example of its output (syscall names are not yet supported, they will appear as numbers):


           .ft C
           syscall events:

           event                                          count
           ----------------------------------------  -----------
           sys_write                                     455067
           sys_getdents                                    4072
           sys_close                                       3037
           sys_swapoff                                     1769
           sys_read                                         923
           sys_sched_setparam                               826
           sys_open                                         331
           sys_newfstat                                     326
           sys_mmap                                         217
           sys_munmap                                       216
           sys_futex                                        141
           sys_select                                       102
           sys_poll                                          84
           sys_setitimer                                     12
           sys_writev                                         8
           15                                                 8
           sys_lseek                                          7
           sys_rt_sigprocmask                                 6
           sys_wait4                                          3
           sys_ioctl                                          3
           sys_set_robust_list                                1
           sys_exit                                           1
           56                                                 1
           sys_access                                         1
           .ft


       Basically our task is to keep a per-syscall tally that gets updated every time a system call occurs in the
       system. Our script will do that, but first we need to record the data that will be processed by that script.
       Theoretically, there are a couple of ways we could do that:

       ?   we could enable every event under the tracing/events/syscalls directory, but this is over 600 syscalls,
           well beyond the number allowable by perf. These individual syscall events will however be useful if we want
           to later use the guidance we get from the general-purpose scripts to drill down and get more detail about
           individual syscalls of interest.

       ?   we can enable the sys_enter and/or sys_exit syscalls found under tracing/events/raw_syscalls. These are
           called for all syscalls; the id field can be used to distinguish between individual syscall numbers.

       For this script, we only need to know that a syscall was entered; we don't care how it exited, so we'll use
       perf record to record only the sys_enter events:


           .ft C
           # perf record -a -e raw_syscalls:sys_enter

           ^C[ perf record: Woken up 1 times to write data ]
           [ perf record: Captured and wrote 56.545 MB perf.data (~2470503 samples) ]
           .ft


       The options basically say to collect data for every syscall event system-wide and multiplex the per-cpu output
       into a single stream. That single stream will be recorded in a file in the current directory called perf.data.

       Once we have a perf.data file containing our data, we can use the -g perf script option to generate a Python
       script that will contain a callback handler for each event type found in the perf.data trace stream (for more
       details, see the STARTER SCRIPTS section).


           .ft C
           # perf script -g python
           generated Python script: perf-script.py

           The output file created also in the current directory is named
           perf-script.py.  Here?s the file in its entirety:

           # perf script event handlers, generated by perf script -g python
           # Licensed under the terms of the GNU GPL License version 2

           # The common_* event handler fields are the most useful fields common to
           # all events.  They don?t necessarily correspond to the ?common_*? fields
           # in the format files.  Those fields not available as handler params can
           # be retrieved using Python functions of the form common_*(context).
           # See the perf-script-python Documentation for the list of available functions.

           import os
           import sys

           sys.path.append(os.environ[?PERF_EXEC_PATH?] + \
                   ?/scripts/python/Perf-Trace-Util/lib/Perf/Trace?)

           from perf_trace_context import *
           from Core import *

           def trace_begin():
                   print "in trace_begin"

           def trace_end():
                   print "in trace_end"

           def raw_syscalls__sys_enter(event_name, context, common_cpu,
                   common_secs, common_nsecs, common_pid, common_comm,
                   id, args):
                           print_header(event_name, common_cpu, common_secs, common_nsecs,
                                   common_pid, common_comm)

                           print "id=%d, args=%s\n" % \
                           (id, args),

           def trace_unhandled(event_name, context, common_cpu, common_secs, common_nsecs,
                           common_pid, common_comm):
                           print_header(event_name, common_cpu, common_secs, common_nsecs,
                           common_pid, common_comm)

           def print_header(event_name, cpu, secs, nsecs, pid, comm):
                   print "%-20s %5u %05u.%09u %8u %-20s " % \
                   (event_name, cpu, secs, nsecs, pid, comm),
           .ft


       At the top is a comment block followed by some import statements and a path append which every perf script
       script should include.

       Following that are a couple generated functions, trace_begin() and trace_end(), which are called at the
       beginning and the end of the script respectively (for more details, see the SCRIPT_LAYOUT section below).

       Following those are the event handler functions generated one for every event in the perf record output. The
       handler functions take the form subsystemevent_name, and contain named parameters, one for each field in the
       event; in this case, there's only one event, raw_syscallssys_enter(). (see the EVENT HANDLERS section below for
       more info on event handlers).

       The final couple of functions are, like the begin and end functions, generated for every script. The first,
       trace_unhandled(), is called every time the script finds an event in the perf.data file that doesn't correspond
       to any event handler in the script. This could mean either that the record step recorded event types that it
       wasn't really interested in, or the script was run against a trace file that doesn't correspond to the script.

       The script generated by -g option simply prints a line for each event found in the trace stream i.e. it
       basically just dumps the event and its parameter values to stdout. The print_header() function is simply a
       utility function used for that purpose. Let's rename the script and run it to see the default output:


           .ft C
           # mv perf-script.py syscall-counts.py
           # perf script -s syscall-counts.py

           raw_syscalls__sys_enter     1 00840.847582083     7506 perf                  id=1, args=
           raw_syscalls__sys_enter     1 00840.847595764     7506 perf                  id=1, args=
           raw_syscalls__sys_enter     1 00840.847620860     7506 perf                  id=1, args=
           raw_syscalls__sys_enter     1 00840.847710478     6533 npviewer.bin          id=78, args=
           raw_syscalls__sys_enter     1 00840.847719204     6533 npviewer.bin          id=142, args=
           raw_syscalls__sys_enter     1 00840.847755445     6533 npviewer.bin          id=3, args=
           raw_syscalls__sys_enter     1 00840.847775601     6533 npviewer.bin          id=3, args=
           raw_syscalls__sys_enter     1 00840.847781820     6533 npviewer.bin          id=3, args=
           .
           .
           .
           .ft


       Of course, for this script, we're not interested in printing every trace event, but rather aggregating it in a
       useful way. So we'll get rid of everything to do with printing as well as the trace_begin() and
       trace_unhandled() functions, which we won't be using. That leaves us with this minimalistic skeleton:


           .ft C
           import os
           import sys

           sys.path.append(os.environ[?PERF_EXEC_PATH?] + \
                   ?/scripts/python/Perf-Trace-Util/lib/Perf/Trace?)

           from perf_trace_context import *
           from Core import *

           def trace_end():
                   print "in trace_end"

           def raw_syscalls__sys_enter(event_name, context, common_cpu,
                   common_secs, common_nsecs, common_pid, common_comm,
                   id, args):
           .ft


       In trace_end(), we'll simply print the results, but first we need to generate some results to print. To do that
       we need to have our sys_enter() handler do the necessary tallying until all events have been counted. A hash
       table indexed by syscall id is a good way to store that information; every time the sys_enter() handler is
       called, we simply increment a count associated with that hash entry indexed by that syscall id:


           .ft C
             syscalls = autodict()

             try:
               syscalls[id] += 1
             except TypeError:
               syscalls[id] = 1
           .ft


       The syscalls autodict object is a special kind of Python dictionary (implemented in Core.py) that implements
       Perl's autovivifying hashes in Python i.e. with autovivifying hashes, you can assign nested hash values without
       having to go to the trouble of creating intermediate levels if they don't exist e.g syscalls[comm][pid][id] = 1
       will create the intermediate hash levels and finally assign the value 1 to the hash entry for id (because the
       value being assigned isn't a hash object itself, the initial value is assigned in the TypeError exception.
       Well, there may be a better way to do this in Python but that's what works for now).

       Putting that code into the raw_syscalls__sys_enter() handler, we effectively end up with a single-level
       dictionary keyed on syscall id and having the counts we've tallied as values.

       The print_syscall_totals() function iterates over the entries in the dictionary and displays a line for each
       entry containing the syscall name (the dictonary keys contain the syscall ids, which are passed to the Util
       function syscall_name(), which translates the raw syscall numbers to the corresponding syscall name strings).
       The output is displayed after all the events in the trace have been processed, by calling the
       print_syscall_totals() function from the trace_end() handler called at the end of script processing.

       The final script producing the output shown above is shown in its entirety below (syscall_name() helper is not
       yet available, you can only deal with id's for now):


           .ft C
           import os
           import sys

           sys.path.append(os.environ[?PERF_EXEC_PATH?] + \
                   ?/scripts/python/Perf-Trace-Util/lib/Perf/Trace?)

           from perf_trace_context import *
           from Core import *
           from Util import *

           syscalls = autodict()

           def trace_end():
                   print_syscall_totals()

           def raw_syscalls__sys_enter(event_name, context, common_cpu,
                   common_secs, common_nsecs, common_pid, common_comm,
                   id, args):
                   try:
                           syscalls[id] += 1
                   except TypeError:
                           syscalls[id] = 1

           def print_syscall_totals():
               if for_comm is not None:
                       print "\nsyscall events for %s:\n\n" % (for_comm),
               else:
                       print "\nsyscall events:\n\n",

               print "%-40s  %10s\n" % ("event", "count"),
               print "%-40s  %10s\n" % ("----------------------------------------", \
                                            "-----------"),

               for id, val in sorted(syscalls.iteritems(), key = lambda(k, v): (v, k), \
                                             reverse = True):
                       print "%-40s  %10d\n" % (syscall_name(id), val),
           .ft


       The script can be run just as before:

           # perf script -s syscall-counts.py

       So those are the essential steps in writing and running a script. The process can be generalized to any
       tracepoint or set of tracepoints you're interested in - basically find the tracepoint(s) you're interested in
       by looking at the list of available events shown by perf list and/or look in /sys/kernel/debug/tracing events
       for detailed event and field info, record the corresponding trace data using perf record, passing it the list
       of interesting events, generate a skeleton script using perf script -g python and modify the code to aggregate
       and display it for your particular needs.

       After you've done that you may end up with a general-purpose script that you want to keep around and have
       available for future use. By writing a couple of very simple shell scripts and putting them in the right place,
       you can have your script listed alongside the other scripts listed by the perf script -l command e.g.:


           .ft C
           root@tropicana:~# perf script -l
           List of available trace scripts:
             wakeup-latency                       system-wide min/max/avg wakeup latency
             rw-by-file <comm>                    r/w activity for a program, by file
             rw-by-pid                            system-wide r/w activity
           .ft


       A nice side effect of doing this is that you also then capture the probably lengthy perf record command needed
       to record the events for the script.

       To have the script appear as a built-in script, you write two simple scripts, one for recording and one for
       reporting.

       The record script is a shell script with the same base name as your script, but with -record appended. The
       shell script should be put into the perf/scripts/python/bin directory in the kernel source tree. In that
       script, you write the perf record command-line needed for your script:


           .ft C
           # cat kernel-source/tools/perf/scripts/python/bin/syscall-counts-record

           #!/bin/bash
           perf record -a -e raw_syscalls:sys_enter
           .ft


       The report script is also a shell script with the same base name as your script, but with -report appended. It
       should also be located in the perf/scripts/python/bin directory. In that script, you write the perf script -s
       command-line needed for running your script:


           .ft C
           # cat kernel-source/tools/perf/scripts/python/bin/syscall-counts-report

           #!/bin/bash
           # description: system-wide syscall counts
           perf script -s ~/libexec/perf-core/scripts/python/syscall-counts.py
           .ft


       Note that the location of the Python script given in the shell script is in the
       libexec/perf-core/scripts/python directory - this is where the script will be copied by make install when you
       install perf. For the installation to install your script there, your script needs to be located in the
       perf/scripts/python directory in the kernel source tree:


           .ft C
           # ls -al kernel-source/tools/perf/scripts/python

           root@tropicana:/home/trz/src/tip# ls -al tools/perf/scripts/python
           total 32
           drwxr-xr-x 4 trz trz 4096 2010-01-26 22:30 .
           drwxr-xr-x 4 trz trz 4096 2010-01-26 22:29 ..
           drwxr-xr-x 2 trz trz 4096 2010-01-26 22:29 bin
           -rw-r--r-- 1 trz trz 2548 2010-01-26 22:29 check-perf-script.py
           drwxr-xr-x 3 trz trz 4096 2010-01-26 22:49 Perf-Trace-Util
           -rw-r--r-- 1 trz trz 1462 2010-01-26 22:30 syscall-counts.py
           .ft


       Once you've done that (don't forget to do a new make install, otherwise your script won't show up at run-time),
       perf script -l should show a new entry for your script:


           .ft C
           root@tropicana:~# perf script -l
           List of available trace scripts:
             wakeup-latency                       system-wide min/max/avg wakeup latency
             rw-by-file <comm>                    r/w activity for a program, by file
             rw-by-pid                            system-wide r/w activity
             syscall-counts                       system-wide syscall counts
           .ft


       You can now perform the record step via perf script record:

           # perf script record syscall-counts

       and display the output using perf script report:

           # perf script report syscall-counts

STARTER SCRIPTS
       You can quickly get started writing a script for a particular set of trace data by generating a skeleton script
       using perf script -g python in the same directory as an existing perf.data trace file. That will generate a
       starter script containing a handler for each of the event types in the trace file; it simply prints every
       available field for each event in the trace file.

       You can also look at the existing scripts in ~/libexec/perf-core/scripts/python for typical examples showing
       how to do basic things like aggregate event data, print results, etc. Also, the check-perf-script.py script,
       while not interesting for its results, attempts to exercise all of the main scripting features.

EVENT HANDLERS
       When perf script is invoked using a trace script, a user-defined handler function is called for each event in
       the trace. If there's no handler function defined for a given event type, the event is ignored (or passed to a
       trace_handled function, see below) and the next event is processed.

       Most of the event's field values are passed as arguments to the handler function; some of the less common ones
       aren't - those are available as calls back into the perf executable (see below).

       As an example, the following perf record command can be used to record all sched_wakeup events in the system:

           # perf record -a -e sched:sched_wakeup

       Traces meant to be processed using a script should be recorded with the above option: -a to enable system-wide
       collection.

       The format file for the sched_wakep event defines the following fields (see
       /sys/kernel/debug/tracing/events/sched/sched_wakeup/format):


           .ft C
            format:
                   field:unsigned short common_type;
                   field:unsigned char common_flags;
                   field:unsigned char common_preempt_count;
                   field:int common_pid;

                   field:char comm[TASK_COMM_LEN];
                   field:pid_t pid;
                   field:int prio;
                   field:int success;
                   field:int target_cpu;
           .ft


       The handler function for this event would be defined as:


           .ft C
           def sched__sched_wakeup(event_name, context, common_cpu, common_secs,
                  common_nsecs, common_pid, common_comm,
                  comm, pid, prio, success, target_cpu):
                  pass
           .ft


       The handler function takes the form subsystem__event_name.

       The common_* arguments in the handler's argument list are the set of arguments passed to all event handlers;
       some of the fields correspond to the common_* fields in the format file, but some are synthesized, and some of
       the common_* fields aren't common enough to to be passed to every event as arguments but are available as
       library functions.

       Here's a brief description of each of the invariant event args:

           event_name                 the name of the event as text
           context                    an opaque ?cookie? used in calls back into perf
           common_cpu                 the cpu the event occurred on
           common_secs                the secs portion of the event timestamp
           common_nsecs               the nsecs portion of the event timestamp
           common_pid                 the pid of the current task
           common_comm                the name of the current process

       All of the remaining fields in the event's format file have counterparts as handler function arguments of the
       same name, as can be seen in the example above.

       The above provides the basics needed to directly access every field of every event in a trace, which covers 90%
       of what you need to know to write a useful trace script. The sections below cover the rest.

SCRIPT LAYOUT
       Every perf script Python script should start by setting up a Python module search path and ?import'ing a few
       support modules (see module descriptions below):


           .ft C
            import os
            import sys

            sys.path.append(os.environ[?PERF_EXEC_PATH?] + \
                         ?/scripts/python/Perf-Trace-Util/lib/Perf/Trace?)

            from perf_trace_context import *
            from Core import *
           .ft


       The rest of the script can contain handler functions and support functions in any order.

       Aside from the event handler functions discussed above, every script can implement a set of optional functions:

       trace_begin, if defined, is called before any event is processed and gives scripts a chance to do setup tasks:


           .ft C
           def trace_begin:
               pass
           .ft


       trace_end, if defined, is called after all events have been processed and gives scripts a chance to do
       end-of-script tasks, such as display results:


           .ft C
           def trace_end:
               pass
           .ft


       trace_unhandled, if defined, is called after for any event that doesn't have a handler explicitly defined for
       it. The standard set of common arguments are passed into it:


           .ft C
           def trace_unhandled(event_name, context, common_cpu, common_secs,
                   common_nsecs, common_pid, common_comm):
               pass
           .ft


       The remaining sections provide descriptions of each of the available built-in perf script Python modules and
       their associated functions.

AVAILABLE MODULES AND FUNCTIONS
       The following sections describe the functions and variables available via the various perf script Python
       modules. To use the functions and variables from the given module, add the corresponding from XXXX import line
       to your perf script script.

   Core.py Module
       These functions provide some essential functions to user scripts.

       The flag_str and symbol_str functions provide human-readable strings for flag and symbolic fields. These
       correspond to the strings and values parsed from the print fmt fields of the event format files:

           flag_str(event_name, field_name, field_value) - returns the string represention corresponding to field_value for the flag field field_name of event event_name
           symbol_str(event_name, field_name, field_value) - returns the string represention corresponding to field_value for the symbolic field field_name of event event_name

       The autodict function returns a special kind of Python dictionary that implements Perl's autovivifying hashes
       in Python i.e. with autovivifying hashes, you can assign nested hash values without having to go to the trouble
       of creating intermediate levels if they don't exist.

           autodict() - returns an autovivifying dictionary instance

   perf_trace_context Module
       Some of the common fields in the event format file aren't all that common, but need to be made accessible to
       user scripts nonetheless.

       perf_trace_context defines a set of functions that can be used to access this data in the context of the
       current event. Each of these functions expects a context variable, which is the same as the context variable
       passed into every event handler as the second argument.

           common_pc(context) - returns common_preempt count for the current event
           common_flags(context) - returns common_flags for the current event
           common_lock_depth(context) - returns common_lock_depth for the current event

   Util.py Module
       Various utility functions for use with perf script:

           nsecs(secs, nsecs) - returns total nsecs given secs/nsecs pair
           nsecs_secs(nsecs) - returns whole secs portion given nsecs
           nsecs_nsecs(nsecs) - returns nsecs remainder given nsecs
           nsecs_str(nsecs) - returns printable string in the form secs.nsecs
           avg(total, n) - returns average given a sum and a total number of values

SEE ALSO
       perf-script(1)



perf                              06/22/2017             PERF-SCRIPT-PYTHON(1)