# perf-script-perl

## 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/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
    


* * *