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Subject[RFC][PATCH 6/7] perf trace: Add Documentation for perf trace Perl support
Adds perf-trace-perl Documentation and a link to it from the
perf-trace page.

Signed-off-by: Tom Zanussi <>
tools/perf/Documentation/perf-trace-perl.txt | 219 ++++++++++++++++++++++++++
tools/perf/Documentation/perf-trace.txt | 11 ++-
2 files changed, 229 insertions(+), 1 deletions(-)
create mode 100644 tools/perf/Documentation/perf-trace-perl.txt

diff --git a/tools/perf/Documentation/perf-trace-perl.txt b/tools/perf/Documentation/perf-trace-perl.txt
new file mode 100644
index 0000000..c5f55f4
--- /dev/null
+++ b/tools/perf/Documentation/perf-trace-perl.txt
@@ -0,0 +1,219 @@
+perf-trace-perl - Process trace data with a Perl script
+'perf trace' [-s [lang]:script[.ext] ]
+This perf trace option is used to process perf trace 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.
+You can avoid reading the rest of this document by running 'perf trace
+-g perl' in the same directory as an existing 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 script, while not interesting for its results,
+attempts to exercise all of the main scripting features.
+When perf trace 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 -c 1 -f -a -M -R -e sched:sched_wakeup
+Traces meant to be processed using a script should be recorded with
+the above options: -c 1 says to sample every event, -a to enable
+system-wide collection, -M to multiplex the output, and -R to collect
+raw samples.
+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:int common_lock_depth;
+ 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:
+sub sched::sched_wakeup
+ my ($event_name, $context, $common_cpu, $common_secs,
+ $common_nsecs, $common_pid, $common_comm,
+ $comm, $pid, $prio, $success, $target_cpu) = @_;
+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
+ $common_comm the name of the current process
+All of the remaining fields in the event's format file have
+counterparts as handler function arguments of the same name, as can be
+seen in the example above.
+The above provides the basics needed to directly access every field of
+every event in a trace, which covers 90% of what you need to know to
+write a useful trace script. The sections below cover the rest.
+Every perf trace Perl script should start by setting up a Perl module
+search path and 'use'ing a few support modules (see module
+descriptions below):
+ use lib "$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;
+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:
+ sub trace_begin
+ {
+ }
+*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:
+sub trace_end
+*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:
+sub trace_unhandled
+ my ($event_name, $context, $common_cpu, $common_secs,
+ $common_nsecs, $common_pid, $common_comm) = @_;
+The remaining sections provide descriptions of each of the available
+built-in perf trace Perl modules and their associated functions.
+The following sections describe the functions and variables available
+via the various Perf::Trace::* Perl modules. To use the functions and
+variables from the given module, add the corresponding 'use
+Perf::Trace::XXX' line to your perf trace script.
+Perf::Trace::Core Module
+These functions provide some essential functions to user scripts.
+The *flag_str* and *symbol_str* functions provide human-readable
+strings for flag and symbolic fields. These correspond to the strings
+and values parsed from the 'print fmt' fields of the event format
+ flag_str($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
+ common_pc($context) - returns common_preempt count for the current event
+ common_flags($context) - returns common_flags for the current event
+ common_lock_depth($context) - returns common_lock_depth for the current event
+Perf::Trace::Util Module
+Various utility functions for use with perf trace:
+ nsecs($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
diff --git a/tools/perf/Documentation/perf-trace.txt b/tools/perf/Documentation/perf-trace.txt
index 41ed753..07065ef 100644
--- a/tools/perf/Documentation/perf-trace.txt
+++ b/tools/perf/Documentation/perf-trace.txt
@@ -20,6 +20,15 @@ OPTIONS
Display verbose dump of the trace data.

+ Process trace data with the given script ([lang]:script[.ext]).
+ Generate perf-trace.[ext] starter script for given language,
+ using current
+linkperf:perf-record[1], linkperf:perf-trace-perl[1]

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