| perf-script-python(1) |
| ==================== |
| |
| NAME |
| ---- |
| perf-script-python - Process trace data with a Python script |
| |
| SYNOPSIS |
| -------- |
| [verse] |
| '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): |
| |
| ---- |
| 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 |
| ---- |
| |
| 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: |
| |
| ---- |
| # 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) ] |
| ---- |
| |
| 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). |
| |
| ---- |
| # 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), |
| ---- |
| |
| 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 subsystem__event_name, and contain named parameters, one for |
| each field in the event; in this case, there's only one event, |
| raw_syscalls__sys_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: |
| |
| ---- |
| # 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= |
| . |
| . |
| . |
| ---- |
| |
| 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: |
| |
| ---- |
| 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): |
| ---- |
| |
| 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: |
| |
| ---- |
| syscalls = autodict() |
| |
| try: |
| syscalls[id] += 1 |
| except TypeError: |
| syscalls[id] = 1 |
| ---- |
| |
| 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): |
| |
| ---- |
| 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), |
| ---- |
| |
| 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.: |
| |
| ---- |
| root@tropicana:~# perf script -l |
| List of available trace scripts: |
| workqueue-stats workqueue stats (ins/exe/create/destroy) |
| 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 |
| ---- |
| |
| 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: |
| |
| ---- |
| # cat kernel-source/tools/perf/scripts/python/bin/syscall-counts-record |
| |
| #!/bin/bash |
| perf record -a -e raw_syscalls:sys_enter |
| ---- |
| |
| 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: |
| |
| ---- |
| # 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 |
| ---- |
| |
| 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: |
| |
| ---- |
| # 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 |
| ---- |
| |
| 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: |
| |
| ---- |
| root@tropicana:~# perf script -l |
| List of available trace scripts: |
| workqueue-stats workqueue stats (ins/exe/create/destroy) |
| 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 |
| ---- |
| |
| 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): |
| |
| ---- |
| 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; |
| ---- |
| |
| The handler function for this event would be defined as: |
| |
| ---- |
| def sched__sched_wakeup(event_name, context, common_cpu, common_secs, |
| common_nsecs, common_pid, common_comm, |
| comm, pid, prio, success, target_cpu): |
| pass |
| ---- |
| |
| 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): |
| |
| ---- |
| 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 * |
| ---- |
| |
| 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: |
| |
| ---- |
| def trace_begin: |
| pass |
| ---- |
| |
| *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: |
| |
| ---- |
| def trace_end: |
| pass |
| ---- |
| |
| *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: |
| |
| ---- |
| def trace_unhandled(event_name, context, common_cpu, common_secs, |
| common_nsecs, common_pid, common_comm): |
| pass |
| ---- |
| |
| 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 |
| -------- |
| linkperf:perf-script[1] |