NAME

       perf-script-perl - Process trace data with a Perl script

SYNOPSIS

       perf script [-s [Perl]:script[.pl] ]

DESCRIPTION

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

STARTER SCRIPTS

       You can avoid reading the rest of this document by running perf script -g perl 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/perl for typical
       examples showing how to do basic things like aggregate event data, print results, etc.
       Also, the check-perf-script.pl 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_unhandled 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_wakeup 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
           sub sched::sched_wakeup
           {
              my ($event_name, $context, $common_cpu, $common_secs,
                  $common_nsecs, $common_pid, $common_comm,
                  $comm, $pid, $prio, $success, $target_cpu) = @_;
           }
           .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 Perl script should start by setting up a Perl module search path and
       'use’ing a few support modules (see module descriptions below):

           .ft C
            use lib "$ENV{'PERF_EXEC_PATH'}/scripts/perl/Perf-Trace-Util/lib";
            use lib "./Perf-Trace-Util/lib";
            use Perf::Trace::Core;
            use Perf::Trace::Context;
            use Perf::Trace::Util;
           .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
            sub trace_begin
            {
            }
           .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
           sub trace_end
           {
           }
           .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
           sub trace_unhandled
           {
               my ($event_name, $context, $common_cpu, $common_secs,
                   $common_nsecs, $common_pid, $common_comm) = @_;
           }
           .ft

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

AVAILABLE MODULES AND FUNCTIONS

       The following sections describe the functions and variables available via the various
       Perf::Trace::* Perl modules. To use the functions and variables from the given module, add
       the corresponding use Perf::Trace::XXX line to your perf script script.

   Perf::Trace::Core 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 representation 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 representation corresponding to $field_value for the symbolic field $field_name of event $event_name

   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

   Perf::Trace::Util 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)