PERF-SCRIPT-PERL(1) perf Manual PERF-SCRIPT-PERL(1)NAMEperf-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_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:int common_lock_depth;
field:char comm[TASK_COMM_LEN];
field:pid_t pid;
field:int prio;
field:int success;
field:int target_cpu;
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The handler function for this event would be defined as:
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sub sched::sched_wakeup
{
my ($event_name, $context, $common_cpu, $common_secs,
$common_nsecs, $common_pid, $common_comm,
$comm, $pid, $prio, $success, $target_cpu) = @_;
}
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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
$common_comm the name of the current process
All of the remaining fields in the event’s format file have
counterparts as handler function arguments of the same name, as can be
seen in the example above.
The above provides the basics needed to directly access every field of
every event in a trace, which covers 90% of what you need to know to
write a useful trace script. The sections below cover the rest.
SCRIPT LAYOUT
Every perf script Perl script should start by setting up a Perl module
search path and ´use’ing a few support modules (see module descriptions
below):
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use lib "$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;
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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:
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sub trace_begin
{
}
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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:
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sub trace_end
{
}
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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:
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sub trace_unhandled
{
my ($event_name, $context, $common_cpu, $common_secs,
$common_nsecs, $common_pid, $common_comm) = @_;
}
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The remaining sections provide descriptions of each of the available
built-in perf script Perl modules and their associated functions.
AVAILABLE MODULES AND FUNCTIONS
The following sections describe the functions and variables available
via the various Perf::Trace::* Perl modules. To use the functions and
variables from the given module, add the corresponding use
Perf::Trace::XXX line to your perf script script.
Perf::Trace::Core Module
These functions provide some essential functions to user scripts.
The flag_str and symbol_str functions provide human-readable strings
for flag and symbolic fields. These correspond to the strings and
values parsed from the print fmt fields of the event format files:
flag_str($event_name, $field_name, $field_value) - returns the string 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
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 ALSOperf-script(1)perf 11/21/2013 PERF-SCRIPT-PERL(1)
