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perf-probe

NAME

perf-probe - Define new dynamic tracepoints

SYNOPSIS

 perf probe [options] --add=PROBE [...]
 or
 perf probe [options] PROBE
 or
 perf probe [options] --del=[GROUP:]EVENT [...]
 or
 perf probe --list
 or
 perf probe --line=FUNC[:RLN[+NUM|:RLN2]]|SRC:ALN[+NUM|:ALN2]
 

DESCRIPTION

This command defines dynamic tracepoint events, by symbol and registers without debuginfo, or by C expressions (C line numbers, C function names, and C local variables) with debuginfo.

OPTIONS

-k, --vmlinux=PATH

Specify vmlinux path which has debuginfo (Dwarf binary).

-v, --verbose

Be more verbose (show parsed arguments, etc).

-a, --add=

Define a probe event (see PROBE SYNTAX for detail).

-d, --del=

Delete probe events. This accepts glob wildcards(*, ?) and character classes(e.g. [a-z], [!A-Z]).

-l, --list

List up current probe events.

-L, --line=

Show source code lines which can be probed. This needs an argument which specifies a range of the source code. (see LINE SYNTAX for detail)

-f, --force

Forcibly add events with existing name.

-n, --dry-run

Dry run. With this option, --add and --del doesncqt execute actual adding and removal operations.

--max-probes

Set the maximum number of probe points for an event. Default is 128.

PROBE SYNTAX

Probe points are defined by following syntax.

 1) Define event based on function name
  [EVENT=]FUNC[@SRC][:RLN|+OFFS|%return|;PTN] [ARG ...]
 

 2) Define event based on source file with line number
  [EVENT=]SRC:ALN [ARG ...]
 

 3) Define event based on source file with lazy pattern
  [EVENT=]SRC;PTN [ARG ...]
 

EVENT specifies the name of new event, if omitted, it will be set the name of the probed function. Currently, event group name is set as probe. FUNC specifies a probed function name, and it may have one of the following options; +OFFS is the offset from function entry address in bytes, :RLN is the relative-line number from function entry line, and %return means that it probes function return. And ;PTN means lazy matching pattern (see LAZY MATCHING). Note that ;PTN must be the end of the probe point definition. In addition, @SRC specifies a source file which has that function. It is also possible to specify a probe point by the source line number or lazy matching by using SRC:ALN or SRC;PTN syntax, where SRC is the source file path, :ALN is the line number and ;PTN is the lazy matching pattern. ARG specifies the arguments of this probe point, (see PROBE ARGUMENT).

PROBE ARGUMENT

Each probe argument follows below syntax.

 [NAME=]LOCALVAR|$retval|%REG|@SYMBOL[:TYPE]
 

NAME specifies the name of this argument (optional). You can use the name of local variable, local data structure member (e.g. var->field, var.field2), or kprobe-tracer argument format (e.g. $retval, %ax, etc). Note that the name of this argument will be set as the last member name if you specify a local data structure member (e.g. field2 for var->field1.field2.) TYPE casts the type of this argument (optional). If omitted, perf probe automatically set the type based on debuginfo.

LINE SYNTAX

Line range is descripted by following syntax.

 "FUNC[:RLN[+NUM|-RLN2]]|SRC:ALN[+NUM|-ALN2]"
 

FUNC specifies the function name of showing lines. RLN is the start line number from function entry line, and RLN2 is the end line number. As same as probe syntax, SRC means the source file path, ALN is start line number, and ALN2 is end line number in the file. It is also possible to specify how many lines to show by using NUM. So, "source.c:100-120" shows lines between 100th to l20th in source.c file. And "func:10+20" shows 20 lines from 10th line of func function.

LAZY MATCHING

 The lazy line matching is similar to glob matching but ignoring spaces in both of pattern and target. So this accepts wildcards('*', '?') and character classes(e.g. [a-z], [!A-Z]).
 

e.g. a=* can matches a=b, a = b, a == b and so on.

This provides some sort of flexibility and robustness to probe point definitions against minor code changes. For example, actual 10th line of schedule() can be moved easily by modifying schedule(), but the same line matching rq=cpu_rq* may still exist in the function.)

EXAMPLES

Display which lines in schedule() can be probed:

 ./perf probe --line schedule
 

Add a probe on schedule() function 12th line with recording cpu local variable:

 ./perf probe schedule:12 cpu
 or
 ./perf probe --add='schedule:12 cpu'
 

 this will add one or more probes which has the name start with "schedule".
 

 Add probes on lines in schedule() function which calls update_rq_clock().
 

 ./perf probe 'schedule;update_rq_clock*'
 or
 ./perf probe --add='schedule;update_rq_clock*'
 

Delete all probes on schedule().

 ./perf probe --del='schedule*'
 

SEE ALSO

perf-trace(1), perf-record(1)