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STAPPROBES(3stap) STAPPROBES(3stap)
NAME
stapprobes - systemtap probe points
DESCRIPTION
The following sections enumerate the variety of probe points supported by the systemtap translator, and some of the addi-
tional aliases defined by standard tapset scripts. Many are individually documented in the 3stap manual section, with
the probe:: prefix.
The general probe point syntax is a dotted-symbol sequence. This allows a breakdown of the event namespace into parts,
somewhat like the Domain Name System does on the Internet. Each component identifier may be parametrized by a string or
number literal, with a syntax like a function call. A component may include a "*" character, to expand to a set of
matching probe points. It may also include "**" to match multiple sequential components at once. Probe aliases likewise
expand to other probe points. Each and every resulting probe point is normally resolved to some low-level system instru-
mentation facility (e.g., a kprobe address, marker, or a timer configuration), otherwise the elaboration phase will fail.
However, a probe point may be followed by a "?" character, to indicate that it is optional, and that no error should
result if it fails to resolve. Optionalness passes down through all levels of alias/wildcard expansion. Alternately, a
probe point may be followed by a "!" character, to indicate that it is both optional and sufficient. (Think vaguely of
the Prolog cut operator.) If it does resolve, then no further probe points in the same comma-separated list will be
resolved. Therefore, the "!" sufficiency mark only makes sense in a list of probe point alternatives.
Additionally, a probe point may be followed by a "if (expr)" statement, in order to enable/disable the probe point on-
the-fly. With the "if" statement, if the "expr" is false when the probe point is hit, the whole probe body including
alias's body is skipped. The condition is stacked up through all levels of alias/wildcard expansion. So the final condi-
tion becomes the logical-and of conditions of all expanded alias/wildcard.
These are all syntactically valid probe points. (They are generally semantically invalid, depending on the contents of
the tapsets, and the versions of kernel/user software installed.)
kernel.function("foo").return
process("/bin/vi").statement(0x2222)
end
syscall.*
sys**open
kernel.function("no_such_function") ?
module("awol").function("no_such_function") !
signal.*? if (switch)
kprobe.function("foo")
Probes may be broadly classified into "synchronous" and "asynchronous". A "synchronous" event is deemed to occur when
any processor executes an instruction matched by the specification. This gives these probes a reference point (instruc-
tion address) from which more contextual data may be available. Other families of probe points refer to "asynchronous"
events such as timers/counters rolling over, where there is no fixed reference point that is related. Each probe point
specification may match multiple locations (for example, using wildcards or aliases), and all them are then probed. A
probe declaration may also contain several comma-separated specifications, all of which are probed.
DWARF DEBUGINFO
Resolving some probe points requires DWARF debuginfo or "debug symbols" for the specific part being instrumented. For
some others, DWARF is automatically synthesized on the fly from source code header files. For others, it is not needed
at all. Since a systemtap script may use any mixture of probe points together, the union of their DWARF requirements has
to be met on the computer where script compilation occurs. (See the --use-server option and the stap-server(8) man page
for information about the remote compilation facility, which allows these requirements to be met on a different machine.)
The following point lists many of the available probe point families, to classify them with respect to their need for
DWARF debuginfo.
DWARF AUTO-DWARF NON-DWARF
kernel.function, .statement kernel.trace kernel.mark
module.function, .statement process.mark
process.function, .statement begin, end, error, never
process.mark (backup) timer
perf
procfs
kernel.statement.absolute
kernel.data
kprobe.function
process.statement.absolute
process.begin, .end, .error
PROBE POINT FAMILIES
BEGIN/END/ERROR
The probe points begin and end are defined by the translator to refer to the time of session startup and shutdown. All
"begin" probe handlers are run, in some sequence, during the startup of the session. All global variables will have been
initialized prior to this point. All "end" probes are run, in some sequence, during the normal shutdown of a session,
such as in the aftermath of an exit () function call, or an interruption from the user. In the case of an error-trig-
gered shutdown, "end" probes are not run. There are no target variables available in either context.
If the order of execution among "begin" or "end" probes is significant, then an optional sequence number may be provided:
begin(N)
end(N)
The number N may be positive or negative. The probe handlers are run in increasing order, and the order between handlers
with the same sequence number is unspecified. When "begin" or "end" are given without a sequence, they are effectively
sequence zero.
The error probe point is similar to the end probe, except that each such probe handler run when the session ends after
errors have occurred. In such cases, "end" probes are skipped, but each "error" probe is still attempted. This kind of
probe can be used to clean up or emit a "final gasp". It may also be numerically parametrized to set a sequence.
NEVER
The probe point never is specially defined by the translator to mean "never". Its probe handler is never run, though its
statements are analyzed for symbol / type correctness as usual. This probe point may be useful in conjunction with op-
tional probes.
SYSCALL
The syscall.* aliases define several hundred probes, too many to summarize here. They are:
syscall.NAME
syscall.NAME.return
Generally, two probes are defined for each normal system call as listed in the syscalls(2) manual page, one for entry and
one for return. Those system calls that never return do not have a corresponding .return probe.
Each probe alias provides a variety of variables. Looking at the tapset source code is the most reliable way. Generally,
each variable listed in the standard manual page is made available as a script-level variable, so syscall.open exposes
filename, flags, and mode. In addition, a standard suite of variables is available at most aliases:
argstr A pretty-printed form of the entire argument list, without parentheses.
name The name of the system call.
retstr For return probes, a pretty-printed form of the system-call result.
As usual for probe aliases, these variables are all simply initialized once from the underlying $context variables, so
that later changes to $context variables are not automatically reflected. Not all probe aliases obey all of these gener-
al guidelines. Please report any bothersome ones you encounter as a bug.
TIMERS
Intervals defined by the standard kernel "jiffies" timer may be used to trigger probe handlers asynchronously. Two probe
point variants are supported by the translator:
timer.jiffies(N)
timer.jiffies(N).randomize(M)
The probe handler is run every N jiffies (a kernel-defined unit of time, typically between 1 and 60 ms). If the "random-
ize" component is given, a linearly distributed random value in the range [-M..+M] is added to N every time the handler
is run. N is restricted to a reasonable range (1 to around a million), and M is restricted to be smaller than N. There
are no target variables provided in either context. It is possible for such probes to be run concurrently on a multi-
processor computer.
Alternatively, intervals may be specified in units of time. There are two probe point variants similar to the jiffies
timer:
timer.ms(N)
timer.ms(N).randomize(M)
Here, N and M are specified in milliseconds, but the full options for units are seconds (s/sec), milliseconds (ms/msec),
microseconds (us/usec), nanoseconds (ns/nsec), and hertz (hz). Randomization is not supported for hertz timers.
The actual resolution of the timers depends on the target kernel. For kernels prior to 2.6.17, timers are limited to
jiffies resolution, so intervals are rounded up to the nearest jiffies interval. After 2.6.17, the implementation uses
hrtimers for tighter precision, though the actual resolution will be arch-dependent. In either case, if the "randomize"
component is given, then the random value will be added to the interval before any rounding occurs.
Profiling timers are also available to provide probes that execute on all CPUs at the rate of the system tick (CON-
FIG_HZ). This probe takes no parameters.
timer.profile
Full context information of the interrupted process is available, making this probe suitable for a time-based sampling
profiler.
DWARF
This family of probe points uses symbolic debugging information for the target kernel/module/program, as may be found in
unstripped executables, or the separate debuginfo packages. They allow placement of probes logically into the execution
path of the target program, by specifying a set of points in the source or object code. When a matching statement exe-
cutes on any processor, the probe handler is run in that context.
Points in a kernel, which are identified by module, source file, line number, function name, or some combination of
these.
Here is a list of probe point families currently supported. The .function variant places a probe near the beginning of
the named function, so that parameters are available as context variables. The .return variant places a probe at the mo-
ment after the return from the named function, so the return value is available as the "$return" context variable. The
.inline modifier for .function filters the results to include only instances of inlined functions. The .call modifier
selects the opposite subset. Inline functions do not have an identifiable return point, so .return is not supported on
.inline probes. The .statement variant places a probe at the exact spot, exposing those local variables that are visible
there.
kernel.function(PATTERN)
kernel.function(PATTERN).call
kernel.function(PATTERN).return
kernel.function(PATTERN).inline
kernel.function(PATTERN).label(LPATTERN)
module(MPATTERN).function(PATTERN)
module(MPATTERN).function(PATTERN).call
module(MPATTERN).function(PATTERN).return
module(MPATTERN).function(PATTERN).inline
module(MPATTERN).function(PATTERN).label(LPATTERN)
kernel.statement(PATTERN)
kernel.statement(ADDRESS).absolute
module(MPATTERN).statement(PATTERN)
process("PATH").function("NAME")
process("PATH").statement("*@FILE.c:123")
process("PATH").library("PATH").function("NAME")
process("PATH").library("PATH").statement("*@FILE.c:123")
process("PATH").function("*").return
process("PATH").function("myfun").label("foo")
process(PID).statement(ADDRESS).absolute
(See the USER-SPACE section below for more information on the process probes.)
In the above list, MPATTERN stands for a string literal that aims to identify the loaded kernel module of interest and
LPATTERN stands for a source program label. Both MPATTERN and LPATTERN may include the "*" "[]", and "?" wildcards.
PATTERN stands for a string literal that aims to identify a point in the program. It is made up of three parts:
o The first part is the name of a function, as would appear in the nm program's output. This part may use the "*" and
"?" wildcarding operators to match multiple names.
o The second part is optional and begins with the "@" character. It is followed by the path to the source file con-
taining the function, which may include a wildcard pattern, such as mm/slab*. If it does not match as is, an implic-
it "*/" is optionally added before the pattern, so that a script need only name the last few components of a possibly
long source directory path.
o Finally, the third part is optional if the file name part was given, and identifies the line number in the source
file preceded by a ":" or a "+". The line number is assumed to be an absolute line number if preceded by a ":", or
relative to the entry of the function if preceded by a "+". All the lines in the function can be matched with ":*".
A range of lines x through y can be matched with ":x-y".
As an alternative, PATTERN may be a numeric constant, indicating an address. Such an address may be found from symbol
tables of the appropriate kernel / module object file. It is verified against known statement code boundaries, and will
be relocated for use at run time.
In guru mode only, absolute kernel-space addresses may be specified with the ".absolute" suffix. Such an address is con-
sidered already relocated, as if it came from /proc/kallsyms, so it cannot be checked against statement/instruction
boundaries.
CONTEXT VARIABLES
Many of the source-level context variables, such as function parameters, locals, globals visible in the compilation unit,
may be visible to probe handlers. They may refer to these variables by prefixing their name with "$" within the scripts.
In addition, a special syntax allows limited traversal of structures, pointers, and arrays. More syntax allows pretty-
printing of individual variables or their groups. See also @cast.
$var refers to an in-scope variable "var". If it's an integer-like type, it will be cast to a 64-bit int for systemtap
script use. String-like pointers (char *) may be copied to systemtap string values using the kernel_string or us-
er_string functions.
$var->field traversal via a structure's or a pointer's field. This
generalized indirection operator may be repeated to follow more levels. Note that the . operator is not used for
plain structure members, only -> for both purposes. (This is because "." is reserved for string concatenation.)
$return
is available in return probes only for functions that are declared with a return value.
$var[N]
indexes into an array. The index given with a literal number or even an arbitrary numeric expression.
A number of operators exist for such basic context variable expressions:
$$vars expands to a character string that is equivalent to
sprintf("parm1=%x ... parmN=%x var1=%x ... varN=%x",
parm1, ..., parmN, var1, ..., varN)
for each variable in scope at the probe point. Some values may be printed as =? if their run-time location cannot be
found.
$$locals
expands to a subset of $$vars for only local variables.
$$parms
expands to a subset of $$vars for only function parameters.
$$return
is available in return probes only. It expands to a string that is equivalent to sprintf("return=%x", $return) if
the probed function has a return value, or else an empty string.
& $EXPR
expands to the address of the given context variable expression, if it is addressable.
@defined($EXPR)
expands to 1 or 0 iff the given context variable expression is resolvable, for use in conditionals such as
@defined($foo->bar) ? $foo->bar : 0
$EXPR$ expands to a string with all of $EXPR's members, equivalent to
sprintf("{.a=%i, .b=%u, .c={...}, .d=[...]}",
$EXPR->a, $EXPR->b)
$EXPR$$
expands to a string with all of $var's members and submembers, equivalent to
sprintf("{.a=%i, .b=%u, .c={.x=%p, .y=%c}, .d=[%i, ...]}",
$EXPR->a, $EXPR->b, $EXPR->c->x, $EXPR->c->y, $EXPR->d[0])
For ".return" probes, context variables other than the "$return" value itself are only available for the function call
parameters. The expressions evaluate to the entry-time values of those variables, since that is when a snapshot is tak-
en. Other local variables are not generally accessible, since by the time a ".return" probe hits, the probed function
will have already returned.
Arbitrary entry-time expressions can also be saved for ".return" probes using the @entry(expr) operator. For example,
one can compute the elapsed time of a function:
probe kernel.function("do_filp_open").return {
println( get_timeofday_us() - @entry(get_timeofday_us()) )
}
DWARFLESS
In absence of debugging information, entry & exit points of kernel & module functions can be probed using the "kprobe"
family of probes. However, these do not permit looking up the arguments / local variables of the function. Following
constructs are supported :
kprobe.function(FUNCTION)
kprobe.function(FUNCTION).return
kprobe.module(NAME).function(FUNCTION)
kprobe.module(NAME).function(FUNCTION).return
kprobe.statement.(ADDRESS).absolute
Probes of type function are recommended for kernel functions, whereas probes of type module are recommended for probing
functions of the specified module. In case the absolute address of a kernel or module function is known, statement
probes can be utilized.
Note that FUNCTION and MODULE names must not contain wildcards, or the probe will not be registered. Also, statement
probes must be run under guru-mode only.
USER-SPACE
Support for user-space probing is available for kernels that are configured with the utrace extensions. See
http://people.redhat.com/roland/utrace/
There are several forms. First, a non-symbolic probe point:
process(PID).statement(ADDRESS).absolute
is analogous to kernel.statement(ADDRESS).absolute in that both use raw (unverified) virtual addresses and provide no
$variables. The target PID parameter must identify a running process, and ADDRESS should identify a valid instruction
address. All threads of that process will be probed.
Second, non-symbolic user-kernel interface events handled by utrace may be probed:
process(PID).begin
process("FULLPATH").begin
process.begin
process(PID).thread.begin
process("FULLPATH").thread.begin
process.thread.begin
process(PID).end
process("FULLPATH").end
process.end
process(PID).thread.end
process("FULLPATH").thread.end
process.thread.end
process(PID).syscall
process("FULLPATH").syscall
process.syscall
process(PID).syscall.return
process("FULLPATH").syscall.return
process.syscall.return
process(PID).insn
process("FULLPATH").insn
process(PID).insn.block
process("FULLPATH").insn.block
A .begin probe gets called when new process described by PID or FULLPATH gets created. A .thread.begin probe gets called
when a new thread described by PID or FULLPATH gets created. A .end probe gets called when process described by PID or
FULLPATH dies. A .thread.end probe gets called when a thread described by PID or FULLPATH dies. A .syscall probe gets
called when a thread described by PID or FULLPATH makes a system call. The system call number is available in the
$syscall context variable, and the first 6 arguments of the system call are available in the $argN (ex. $arg1, $arg2,
...) context variable. A .syscall.return probe gets called when a thread described by PID or FULLPATH returns from a
system call. The system call number is available in the $syscall context variable, and the return value of the system
call is available in the $return context variable. A .insn probe gets called for every single-stepped instruction of the
process described by PID or FULLPATH. A .insn.block probe gets called for every block-stepped instruction of the process
described by PID or FULLPATH.
If a process probe is specified without a PID or FULLPATH, all user threads will be probed. However, if systemtap was
invoked with the -c or -x options, then process probes are restricted to the process hierarchy associated with the target
process. If a process probe is specified without a PID or FULLPATH, but with the -c option, the PATH of the -c cmd will
be heuristically filled into the process PATH.
Third, symbolic static instrumentation compiled into programs and shared libraries may be probed:
process("PATH").mark("LABEL")
process("PATH").provider("PROVIDER").mark("LABEL")
A .mark probe gets called via a static probe which is defined in the application by STAP_PROBE1(PROVIDER,LABEL,arg1),
which is defined in sdt.h. The handle is an application handle, LABEL corresponds to the .mark argument, and arg1 is the
argument. STAP_PROBE1 is used for probes with 1 argument, STAP_PROBE2 is used for probes with 2 arguments, and so on.
The arguments of the probe are available in the context variables $arg1, $arg2, ... An alternative to using the
STAP_PROBE macros is to use the dtrace script to create custom macros. Additionally, the variables $$name and $$provider
are available as parts of the probe point name.
Finally, full symbolic source-level probes in user-space programs and shared libraries are supported. These are exactly
analogous to the symbolic DWARF-based kernel/module probes described above, and expose similar contextual $variables.
process("PATH").function("NAME")
process("PATH").statement("*@FILE.c:123")
process("PATH").library("PATH").function("NAME")
process("PATH").library("PATH").statement("*@FILE.c:123")
process("PATH").function("*").return
process("PATH").function("myfun").label("foo")
Note that for all process probes, PATH names refer to executables that are searched the same way shells do: relative to
the working directory if they contain a "/" character, otherwise in $PATH. If PATH names refer to scripts, the actual
interpreters (specified in the script in the first line after the #! characters) are probed. If PATH is a process compo-
nent parameter referring to shared libraries then all processes that map it at runtime would be selected for probing. If
PATH is a library component parameter referring to shared libraries then the process specified by the process component
would be selected. If the PATH string contains wildcards as in the MPATTERN case, then standard globbing is performed to
find all matching paths. In this case, the $PATH environment variable is not used.
If systemtap was invoked with the -c or -x options, then process probes are restricted to the process hierarchy associat-
ed with the target process.
PROCFS
These probe points allow procfs "files" in /proc/systemtap/MODNAME to be created, read and written using a permission
that may be modified using the proper umask value. Default permissions are 0400 for read probes, and 0200 for write
probes. If both a read and write probe are being used on the same file, a default permission of 0600 will be used. Using
procfs.umask(0040).read would result in a 0404 permission set for the file. (MODNAME is the name of the systemtap mod-
ule). The proc filesystem is a pseudo-filesystem which is used an an interface to kernel data structures. There are sev-
eral probe point variants supported by the translator:
procfs("PATH").read
procfs("PATH").umask(UMASK).read
procfs("PATH").read.maxsize(MAXSIZE)
procfs("PATH").umask(UMASK).maxsize(MAXSIZE)
procfs("PATH").write
procfs("PATH").umask(UMASK).write
procfs.read
procfs.umask(UMASK).read
procfs.read.maxsize(MAXSIZE)
procfs.umask(UMASK).read.maxsize(MAXSIZE)
procfs.write
procfs.umask(UMASK).write
PATH is the file name (relative to /proc/systemtap/MODNAME) to be created. If no PATH is specified (as in the last two
variants above), PATH defaults to "command".
When a user reads /proc/systemtap/MODNAME/PATH, the corresponding procfs read probe is triggered. The string data to be
read should be assigned to a variable named $value, like this:
procfs("PATH").read { $value = "100\n" }
When a user writes into /proc/systemtap/MODNAME/PATH, the corresponding procfs write probe is triggered. The data the
user wrote is available in the string variable named $value, like this:
procfs("PATH").write { printf("user wrote: %s", $value) }
MAXSIZE is the size of the procfs read buffer. Specifying MAXSIZE allows larger procfs output. If no MAXSIZE is speci-
fied, the procfs read buffer defaults to STP_PROCFS_BUFSIZE (which defaults to MAXSTRINGLEN, the maximum length of a
string). If setting the procfs read buffers for more than one file is needed, it may be easiest to override the
STP_PROCFS_BUFSIZE definition. Here's an example of using MAXSIZE:
procfs.read.maxsize(1024) {
$value = "long string..."
$value .= "another long string..."
$value .= "another long string..."
$value .= "another long string..."
}
MARKERS
This family of probe points hooks up to static probing markers inserted into the kernel or modules. These markers are
special macro calls inserted by kernel developers to make probing faster and more reliable than with DWARF-based probes.
Further, DWARF debugging information is not required to probe markers.
Marker probe points begin with kernel. The next part names the marker itself: mark("name"). The marker name string,
which may contain the usual wildcard characters, is matched against the names given to the marker macros when the kernel
and/or module was compiled. Optionally, you can specify format("format"). Specifying the marker format string allows
differentiation between two markers with the same name but different marker format strings.
The handler associated with a marker-based probe may read the optional parameters specified at the macro call site.
These are named $arg1 through $argNN, where NN is the number of parameters supplied by the macro. Number and string pa-
rameters are passed in a type-safe manner.
The marker format string associated with a marker is available in $format. And also the marker name string is available
in $name.
TRACEPOINTS
This family of probe points hooks up to static probing tracepoints inserted into the kernel or modules. As with markers,
these tracepoints are special macro calls inserted by kernel developers to make probing faster and more reliable than
with DWARF-based probes, and DWARF debugging information is not required to probe tracepoints. Tracepoints have an extra
advantage of more strongly-typed parameters than markers.
Tracepoint probes begin with kernel. The next part names the tracepoint itself: trace("name"). The tracepoint name
string, which may contain the usual wildcard characters, is matched against the names defined by the kernel developers in
the tracepoint header files.
The handler associated with a tracepoint-based probe may read the optional parameters specified at the macro call site.
These are named according to the declaration by the tracepoint author. For example, the tracepoint probe ker-
nel.trace("sched_switch") provides the parameters $rq, $prev, and $next. If the parameter is a complex type, as in a
struct pointer, then a script can access fields with the same syntax as DWARF $target variables. Also, tracepoint param-
eters cannot be modified, but in guru-mode a script may modify fields of parameters.
The name of the tracepoint is available in $$name, and a string of name=value pairs for all parameters of the tracepoint
is available in $$vars or $$parms.
HARDWARE BREAKPOINTS
This family of probes is used to set hardware watchpoints for a given
(global) kernel symbol. The probes take three components as inputs :
1. The virtualaddress/name of the kernel symbol to be traced is supplied as argument to this class of probes. ( Probes
for only data segment variables are supported. Probing local variables of a function cannot be done.)
2. Nature of access to be probed : a. .write probe gets triggered when a write happens at the specified address/symbol
name. b. rw probe is triggered when either a read or write happens.
3. .length (optional) Users have the option of specifying the address interval to be probed using "length" constructs.
The user-specified length gets approximated to the closest possible address length that the architecture can support. If
the specified length exceeds the limits imposed by architecture, an error message is flagged and probe registration
fails. Wherever 'length' is not specified, the translator requests a hardware breakpoint probe of length 1. It should be
noted that the "length" construct is not valid with symbol names.
Following constructs are supported :
probe kernel.data(ADDRESS).write
probe kernel.data(ADDRESS).rw
probe kernel.data(ADDRESS).length(LEN).write
probe kernel.data(ADDRESS).length(LEN).rw
probe kernel.data("SYMBOL_NAME").write
probe kernel.data("SYMBOL_NAME").rw
This set of probes make use of the debug registers of the processor, which is a scarce resource. (4 on x86 , 1 on powerpc
) The script translation flags a warning if a user requests more hardware breakpoint probes than the limits set by archi-
tecture. For example,a pass-2 warning is flashed when an input script requests 5 hardware breakpoint probes on an x86
system while x86 architecture supports a maximum of 4 breakpoints. Users are cautioned to set probes judiciously.
EXAMPLES
Here are some example probe points, defining the associated events.
begin, end, end
refers to the startup and normal shutdown of the session. In this case, the handler would run once during startup
and twice during shutdown.
timer.jiffies(1000).randomize(200)
refers to a periodic interrupt, every 1000 +/- 200 jiffies.
kernel.function("*init*"), kernel.function("*exit*")
refers to all kernel functions with "init" or "exit" in the name.
kernel.function("*@kernel/sched.c:240")
refers to any functions within the "kernel/sched.c" file that span line 240. Note that this is not a probe at
the statement at that line number. Use the kernel.statement probe instead.
kernel.mark("getuid")
refers to an STAP_MARK(getuid, ...) macro call in the kernel.
module("usb*").function("*sync*").return
refers to the moment of return from all functions with "sync" in the name in any of the USB drivers.
kernel.statement(0xc0044852)
refers to the first byte of the statement whose compiled instructions include the given address in the kernel.
kernel.statement("*@kernel/sched.c:2917")
refers to the statement of line 2917 within "kernel/sched.c".
kernel.statement("bio_init@fs/bio.c+3")
refers to the statement at line bio_init+3 within "fs/bio.c".
kernel.data("pid_max").write
refers to a hardware preakpoint of type "write" set on pid_max
syscall.*.return
refers to the group of probe aliases with any name in the third position
PERF
This prototype family of probe points interfaces to the kernel "perf event" infrasture for controlling hardware perfor-
mance counters. The events being attached to are described by the "type", "config" fields of the perf_event_attr struc-
ture, and are sampled at an interval governed by the "sample_period" field.
These fields are made available to systemtap scripts using the following syntax:
probe perf.type(NN).config(MM).sample(XX)
probe perf.type(NN).config(MM)
The systemtap probe handler is called once per XX increments of the underlying performance counter. The default sampling
count is 1000000. The range of valid type/config is described by the perf_event_open(2) system call, and/or the lin-
ux/perf_event.h file. Invalid combinations or exhausted hardware counter resources result in errors during systemtap
script startup. Systemtap does not sanity-check the values: it merely passes them through to the kernel for error- and
safety-checking.
SEE ALSO
stap(1), probe::*(3stap), tapset::*(3stap)
STAPPROBES(3stap)
