View Source fprof (tools v4.1)
A Time Profiling Tool using trace to file for minimal runtime performance impact.
This module is used to profile a program to find out how the execution time is used. Tracing to file is used to minimize the runtime performance degradation.
The fprof
module uses tracing to collect profiling data, hence there is no
need for special compilation of any module to be profiled. When it starts
tracing, fprof
will erase all previous tracing in the node and set the
necessary trace flags on the profiling target processes as well as local call
trace on all functions in all loaded modules and all modules to be loaded.
fprof
disable all tracing in the node when it stops tracing.
fprof
presents both own time that is, how much time a function has
used for its own execution, and accumulated time that is, including
called functions. All presented times are collected using trace
timestamps. fprof
tries to collect CPU time timestamps, if the host
machine OS supports it. Therefore, the times can be wallclock times and
OS scheduling will randomly strike all called functions in a
presumably fair way.
However, if the profiling time is short, and the host machine OS does not support high resolution CPU time measurements, a few OS schedulings can show up as ridiculously long execution times for functions doing practically nothing. As an example, it has been observed that a function that more or less just composing a tuple, was running 100 times slower than normal. When tracing was repeated, the execution time was normal.
Profiling is essentially done in 3 steps:
Tracing: to a file. The trace data contains entries for function calls, returns to function, process scheduling, other process related events (for example
spawn
), and garbage collection. All trace entries are timestamped.Profiling: the trace file is read, the execution call stack is simulated, and raw profile data is calculated from the simulated call stack and the trace timestamps. The profile data is stored in the
fprof
server state. During this step the trace data may be dumped in text format to file or console.Analysing: the raw profile data is sorted, filtered and dumped in text format either to file or console. The text format intended to be both readable for a human reader, as well as parsable with the standard erlang parsing tools.
Since fprof
sends trace data to afile, the runtime performance
degradation is minimized, but still far from negligible, especially
for programs that themselves use the filesystem heavily. Where the
trace file is placed is also important, for example, on Unix systems
/tmp
is usually a good choice since it is essentially a RAM disk,
while any network-mounted disk is a bad idea.
fprof
can also skip the file step and trace to a tracer process that does the
profiling in runtime.
Analysis format
This section describes the output format of the analyse/1
function.
The format is parsable with the standard Erlang parsing tools
erl_scan
and erl_parse
, file:consult/1
, or io:read/2
. The
parse format is not described here — it should be easy enough for the
interested reader to try it out. Note that some flags to
analyse/1
will affect the format.
The following example was run on Erlang/OTP R8 on Solaris 8; all OTP internals in this example are version dependent.
As an example, we will use the following function, which is a
slightly modified benchmark function from module file
:
-module(foo).
-export([create_file_slow/2]).
create_file_slow(Name, N) when is_integer(N), N >= 0 ->
{ok, FD} =
file:open(Name, [raw, write, delayed_write, binary]),
if N > 256 ->
ok = file:write(FD,
lists:map(fun (X) -> <<X:32/unsigned>> end,
lists:seq(0, 255))),
ok = create_file_slow(FD, 256, N);
true ->
ok = create_file_slow(FD, 0, N)
end,
ok = file:close(FD).
create_file_slow(FD, M, M) ->
ok;
create_file_slow(FD, M, N) ->
ok = file:write(FD, <<M:32/unsigned>>),
create_file_slow(FD, M+1, N).
Let us have a look at the printout after running:
1> fprof:apply(foo, create_file_slow, [junk, 1024]).
2> fprof:profile().
3> fprof:analyse().
The printout starts with:
%% Analysis results:
{ analysis_options,
[{callers, true},
{sort, acc},
{totals, false},
{details, true}]}.
% CNT ACC OWN
[{ totals, 9627, 1691.119, 1659.074}]. %%%
The CNT
column shows the total number of function calls that was found in the
trace. In the ACC
column is the total time of the trace from first timestamp to
last. And in the OWN
column is the sum of the execution time in functions found
in the trace, not including called functions. In this case it is very close to
the ACC
time since the emulator had practically nothing to do except
executing our test program.
All time values in the printout are in milliseconds.
The printout continues:
% CNT ACC OWN
[{ "<0.28.0>", 9627,undefined, 1659.074}]. %%
This is the printout header of one process. The printout contains only this one
process since we called fprof:apply/3
that traces only the current process.
Therefore the CNT
and OWN
columns perfectly matches the totals above. The ACC
column is undefined since summing the ACC
times of all calls in the process
makes no sense — one would get something like the ACC
value from totals above
multiplied by the average depth of the call stack.
All paragraphs up to the next process header only concerns function calls within this process.
Now we come to something more interesting:
{[{undefined, 0, 1691.076, 0.030}],
{ {fprof,apply_start_stop,4}, 0, 1691.076, 0.030}, %
[{{foo,create_file_slow,2}, 1, 1691.046, 0.103},
{suspend, 1, 0.000, 0.000}]}.
{[{{fprof,apply_start_stop,4}, 1, 1691.046, 0.103}],
{ {foo,create_file_slow,2}, 1, 1691.046, 0.103}, %
[{{file,close,1}, 1, 1398.873, 0.019},
{{foo,create_file_slow,3}, 1, 249.678, 0.029},
{{file,open,2}, 1, 20.778, 0.055},
{{lists,map,2}, 1, 16.590, 0.043},
{{lists,seq,2}, 1, 4.708, 0.017},
{{file,write,2}, 1, 0.316, 0.021}]}.
The printout consists of one paragraph per called function. The function
marked with %
is the one the paragraph concerns — foo:create_file_slow/2
.
Above the marked function are the calling functions — those that has called
the marked, and below are those called by the marked function.
The paragraphs are per default sorted in descending order of the ACC
column for
the marked function. The calling list and called list within one paragraph are
also per default sorted in descending order of their ACC
column.
The columns are:
CNT
- the number of times the function has been calledACC
- the time spent in the function including called functionsOWN
- the time spent in the function not including called functions
The rows for the calling functions contain statistics for the marked function with the constraint that only the occasions when a call was made from the row's function to the marked function are accounted for.
The row for the marked function simply contains the sum of all calling rows.
The rows for the called functions contains statistics for the row's function with the constraint that only the occasions when a call was made from the marked to the row's function are accounted for.
So, we see that foo:create_file_slow/2
used very little time for its own
execution. It spent most of its time in file:close/1
. The function
foo:create_file_slow/3
that writes 3/4 of the file contents is the second
biggest time thief.
We also see that the call to file:write/2
that writes 1/4 of the file contents
takes very little time in itself. What takes time is to build the data
(lists:seq/2
and lists:map/2
).
The function undefined
that has called fprof:apply_start_stop/4
is an
unknown function because that call was not recorded in the trace. It was only
recorded that the execution returned from fprof:apply_start_stop/4
to some
other function above in the call stack, or that the process exited from there.
Let us continue down the printout to find:
{[{{foo,create_file_slow,2}, 1, 249.678, 0.029},
{{foo,create_file_slow,3}, 768, 0.000, 23.294}],
{ {foo,create_file_slow,3}, 769, 249.678, 23.323}, %
[{{file,write,2}, 768, 220.314, 14.539},
{suspend, 57, 6.041, 0.000},
{{foo,create_file_slow,3}, 768, 0.000, 23.294}]}.
If you compare with the code you will see there also that
foo:create_file_slow/3
was called only from foo:create_file_slow/2
and
itself, and called only file:write/2
, note the number of calls to
file:write/2
. But here we see that suspend
was called a few times. This is a
pseudo function that indicates that the process was suspended while executing in
foo:create_file_slow/3
, and since there is no receive
or erlang:yield/0
in
the code, it must be Erlang scheduling suspensions, or the trace file driver
compensating for large file write operations (these are regarded as a schedule
out followed by a schedule in to the same process).
Let us find the suspend
entry:
{[{{file,write,2}, 53, 6.281, 0.000},
{{foo,create_file_slow,3}, 57, 6.041, 0.000},
{{prim_file,drv_command,4}, 50, 4.582, 0.000},
{{prim_file,drv_get_response,1}, 34, 2.986, 0.000},
{{lists,map,2}, 10, 2.104, 0.000},
{{prim_file,write,2}, 17, 1.852, 0.000},
{{erlang,port_command,2}, 15, 1.713, 0.000},
{{prim_file,drv_command,2}, 22, 1.482, 0.000},
{{prim_file,translate_response,2}, 11, 1.441, 0.000},
{{prim_file,'-drv_command/2-fun-0-',1}, 15, 1.340, 0.000},
{{lists,seq,4}, 3, 0.880, 0.000},
{{foo,'-create_file_slow/2-fun-0-',1}, 5, 0.523, 0.000},
{{erlang,bump_reductions,1}, 4, 0.503, 0.000},
{{prim_file,open_int_setopts,3}, 1, 0.165, 0.000},
{{prim_file,i32,4}, 1, 0.109, 0.000},
{{fprof,apply_start_stop,4}, 1, 0.000, 0.000}],
{ suspend, 299, 32.002, 0.000}, %
[ ]}.
We find no particularly long suspend times, so no function seems to have waited
in a receive statement. Actually, prim_file:drv_command/4
contains a receive
statement, but in this test program, the message lies in the process receive
buffer when the receive statement is entered. We also see that the total suspend
time for the test run is small.
The suspend
pseudo function has an OWN
time of zero. This is to prevent
the process total OWN
time from including time in suspension. Whether suspend
time is really ACC
or OWN
time is more of a philosophical question.
Now we look at another interesting pseudo function, garbage_collect
:
{[{{prim_file,drv_command,4}, 25, 0.873, 0.873},
{{prim_file,write,2}, 16, 0.692, 0.692},
{{lists,map,2}, 2, 0.195, 0.195}],
{ garbage_collect, 43, 1.760, 1.760}, %
[ ]}.
Here we see that no function stands out, which is very normal.
The garbage_collect
pseudo function has not an OWN
time of zero like
suspend
, instead it is equal to the ACC
time.
Garbage collection often occurs while a process is suspended, but fprof
hides
this fact by pretending that the suspended function was first unsuspended and
then garbage collected. Otherwise the printout would show garbage_collect
being called from suspend
, but not which function that might have caused the
garbage collection.
Let us now get back to the test code:
{[{{foo,create_file_slow,3}, 768, 220.314, 14.539},
{{foo,create_file_slow,2}, 1, 0.316, 0.021}],
{ {file,write,2}, 769, 220.630, 14.560}, %
[{{prim_file,write,2}, 769, 199.789, 22.573},
{suspend, 53, 6.281, 0.000}]}.
Not unexpectedly, we see that file:write/2
was called from
foo:create_file_slow/3
and foo:create_file_slow/2
. The number of calls in
each case as well as the used time are also confirms the previous results.
We see that file:write/2
only calls prim_file:write/2
, but let us refrain
from digging into the internals of the kernel application.
If we nevertheless do dig down we find the call to the linked-in driver that does the file operations towards the host operating system:
{[{{prim_file,drv_command,4}, 772, 1458.356, 1456.643}],
{ {erlang,port_command,2}, 772, 1458.356, 1456.643}, %
[{suspend, 15, 1.713, 0.000}]}.
This is 86 % of the total run time, and as we saw before it is the close operation the absolutely biggest contributor. We find a comparison ratio a little bit up in the call stack:
{[{{prim_file,close,1}, 1, 1398.748, 0.024},
{{prim_file,write,2}, 769, 174.672, 12.810},
{{prim_file,open_int,4}, 1, 19.755, 0.017},
{{prim_file,open_int_setopts,3}, 1, 0.147, 0.016}],
{ {prim_file,drv_command,2}, 772, 1593.322, 12.867}, %
[{{prim_file,drv_command,4}, 772, 1578.973, 27.265},
{suspend, 22, 1.482, 0.000}]}.
The time for file operations in the linked in driver distributes itself as 1 % for open, 11 % for write, and 87 % for close. All data is probably buffered in the operating system until the close.
The observant reader may notice that the ACC times for
prim_file:drv_command/2
and prim_file:drv_command/4
is not equal between the
paragraphs above, even though it is easy to believe that
prim_file:drv_command/2
is just a passthrough function.
The missing time can be found in the paragraph for prim_file:drv_command/4
where it is evident that not only prim_file:drv_command/2
is called but also a
fun:
{[{{prim_file,drv_command,2}, 772, 1578.973, 27.265}],
{ {prim_file,drv_command,4}, 772, 1578.973, 27.265}, %
[{{erlang,port_command,2}, 772, 1458.356, 1456.643},
{{prim_file,'-drv_command/2-fun-0-',1}, 772, 87.897, 12.736},
{suspend, 50, 4.582, 0.000},
{garbage_collect, 25, 0.873, 0.873}]}.
And some more missing time can be explained by the fact that
prim_file:open_int/4
both calls prim_file:drv_command/2
directly as well as
through prim_file:open_int_setopts/3
, which complicates the picture.
{[{{prim_file,open,2}, 1, 20.309, 0.029},
{{prim_file,open_int,4}, 1, 0.000, 0.057}],
{ {prim_file,open_int,4}, 2, 20.309, 0.086}, %
[{{prim_file,drv_command,2}, 1, 19.755, 0.017},
{{prim_file,open_int_setopts,3}, 1, 0.360, 0.032},
{{prim_file,drv_open,2}, 1, 0.071, 0.030},
{{erlang,list_to_binary,1}, 1, 0.020, 0.020},
{{prim_file,i32,1}, 1, 0.017, 0.017},
{{prim_file,open_int,4}, 1, 0.000, 0.057}]}.
.
.
.
{[{{prim_file,open_int,4}, 1, 0.360, 0.032},
{{prim_file,open_int_setopts,3}, 1, 0.000, 0.016}],
{ {prim_file,open_int_setopts,3}, 2, 0.360, 0.048}, %
[{suspend, 1, 0.165, 0.000},
{{prim_file,drv_command,2}, 1, 0.147, 0.016},
{{prim_file,open_int_setopts,3}, 1, 0.000, 0.016}]}.
Notes
The actual supervision of execution times is in itself a CPU-intensive activity. A message is written on the trace file for every function call that is made by the profiled code.
The ACC
time calculation is sometimes difficult to make correct, since it is
difficult to define. This happens especially when a function occurs in several
instances in the call stack, for example by calling itself perhaps through other
functions and perhaps even non-tail recursively.
To produce sensible results, fprof
tries not to charge any function more than
once for ACC
time. The instance highest up (with longest duration) in the call
stack is chosen.
Sometimes a function can unexpectedly waste a lot (some 10 ms or more depending
on host machine OS) of OWN
(and ACC
) time, even functions that do practically
nothing at all. The problem may be that the OS has chosen to schedule out the
Erlang runtime system process for a while, and if the OS does not support high
resolution CPU time measurements fprof
will use wallclock time for its
calculations, and it will appear as if functions are randomly burning virtual
machine time.
See Also
Summary
Functions
Equivalent to analyse([])
.
Analyses raw profile data in the fprof
server.
Equivalent to apply(Func, Args, [])
.
Calls the given function surrounded by
trace([start, ...])
and
trace(stop)
.
Equivalent to apply({Module, Function}, Args, OptionList)
.
Equivalent to profile([])
.
Compiles a trace into raw profile data held by the fprof
server.
Starts the fprof
server.
Equivalent to stop(normal)
.
Stops the fprof
server.
Starts or stops tracing.
Starts or stop tracing.
Types
-type analyse_option() :: append | callers | {callers, boolean()} | {cols, Cols :: non_neg_integer()} | dest | {dest, Dest :: pid() | (Destfile :: file:filename())} | details | {details, boolean()} | no_callers | no_details | {sort, SortSpec :: acc | own} | totals | {totals, boolean()}.
-type apply_option() :: continue | {procs, PidList :: [pid()]} | start | (TraceStartOption :: trace_option()).
-type profile_option() :: append | dump | {dump, pid() | (Dump :: (Dumpfile :: file:filename() | []))} | file | {file, Filename :: file:filename()} | start | stop.
Functions
-spec analyse() -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term().
Equivalent to analyse([])
.
-spec analyse(OptionName) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: analyse_option(), ServerPid :: pid(), Reason :: term().
Analyses raw profile data in the fprof
server.
If Arg
is an atom, this call is equivalent to analyse([Arg])
.
If Arg
is a a tuple {Option, _}
, this call is equivalent to
analyse([Option])
.
Otherwise Arg
must be a list of valid options.
If called when no raw profile data is available, {error, no_profile}
is returned.
Destfile
is used to call file:open/2
.
Option description:
dest
|{dest, Dest}
- Specifies the destination for the analysis. If this option is not given or it isdest
, the destination will be the caller's group leader, otherwise the destinationDest
is either thepid/0
of an I/O device or a filename. If the filename is[]
,"fprof.analysis"
is used instead.append
- Causes the analysis to be appended to the destination file. This option is only allowed with the{dest, Destfile}
option.{cols, Cols}
- Specifies the number of columns in the analysis text. If this option is not given the number of columns is set to 80.callers
|{callers, true}
- Prints callers and called information in the analysis. This is the default.{callers, false}
|no_callers
- Suppresses the printing of callers and called information in the analysis.{sort, SortSpec}
- Specifies if the analysis should be sorted according to the ACC column, which is the default, or the OWN column. See Analysis Format below.totals
|{totals, true}
- Includes a section containing call statistics for all calls regardless of process, in the analysis.{totals, false}
- Suppresses the totals section in the analysis, which is the default.details
|{details, true}
- Prints call statistics for each process in the analysis. This is the default.{details, false}
|no_details
- Suppresses the call statistics for each process from the analysis.
-spec analyse(OptionName, OptionValue) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term().
Equivalent to analyse([{OptionName, OptionValue}])
.
-spec apply(Func, Args) -> term() when Func :: fun() | {Module :: module(), Function :: atom()}, Args :: [term()].
Equivalent to apply(Func, Args, [])
.
-spec apply(Module, Function, Args) -> term() when Module :: module(), Function :: atom(), Args :: [term()]; (Func, Args, OptionList) -> term() when Func :: fun() | {Module :: module(), Function :: atom()}, Args :: [term()], OptionList :: [Option], Option :: apply_option().
Calls the given function surrounded by
trace([start, ...])
and
trace(stop)
.
If the function arguments (Arg1
, Arg2
, and Arg3
) are Module
(an atom), Function
(an atom), and Args
(a list), the function
will be called using
erlang:apply(Module, Function, Args)
.
If the function arguments are Func
(a fun), Args
(a list), and
OptionList
(a list of options), the fun will be called using
erlang:apply(Func, Args)
.
Some effort is made to keep the trace clean from unnecessary trace messages;
tracing is started and stopped from a spawned process while erlang:apply/2
is called in the current process only surrounded by receive
and send
statements towards the trace starting process. The trace starting process exits
when it is not needed any more.
The TraceStartOption
is any option allowed for trace/1
. The
options [start, {procs, [self() | PidList]} | OptList]
are given to
trace/1
, where OptList
is OptionList
with the
continue
, start
and {procs, _}
options removed.
The continue
option inhibits the call to trace(stop)
and leaves
it up to the caller to stop tracing at a suitable time.
-spec apply(Module, Function, Args, OptionList) -> term() when Module :: module(), Function :: atom(), Args :: [term()], OptionList :: [Option], Option :: apply_option().
Equivalent to apply({Module, Function}, Args, OptionList)
.
-spec profile() -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term().
Equivalent to profile([])
.
-spec profile(OptionName) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), Tracer :: pid(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), Tracer :: pid(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: profile_option(), Tracer :: pid(), ServerPid :: pid(), Reason :: term().
Compiles a trace into raw profile data held by the fprof
server.
If Arg
is an atom, this call is equivalent to profile([Arg])
.
If Arg
is a tuple {OptionName, OptionValue}
,
this call is equivalent to profile([Arg])
.
Otherwise, Arg
must be a list of options.
Dumpfile
is used to call file:open/2
, and Filename
is used to call
dbg:trace_port(file, Filename)
.
The following options are supported:
file
|{file, Filename}
- Reads the fileFilename
and creates raw profile data that is stored in RAM by thefprof
server. If the optionfile
is given, or none of these options are given, the filefprof.trace
is read. The call will return when the whole trace has been read with the return valueok
if successful. This option is not allowed with thestart
orstop
options.dump
|{dump, Dump}
- Specifies the destination for the trace text dump. If this option is not given, no dump is generated, if it isdump
the destination will be the caller's group leader, otherwise the destinationDump
is either the pid of an I/O device or a filename. If the filename is[]
,"fprof.dump"
is used instead. This option cannot be combined with thestop
option.append
- Causes the trace text dump to be appended to the destination file. This option is only allowed with the{dump, Dumpfile}
option.start
- Starts a tracer process that profiles trace data in runtime. The call will return immediately with the return value{ok, Tracer}
if successful. This option is not allowed with thestop
,file
, or{file, Filename}
options.stop
- Stops the tracer process that profiles trace data in runtime. The return value will be valueok
if successful. This option cannot be combined with thestart
,file
, or{file, Filename}
options.
-spec profile(OptionName, OptionValue) -> ok | {ok, Tracer} | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), Tracer :: pid(), ServerPid :: pid(), Reason :: term().
Equivalent to profile([{OptionName, OptionValue}])
.
-spec start() -> {ok, Pid} | {error, {already_started, Pid}} when Pid :: pid().
Starts the fprof
server.
Note that there is seldom any need to call this function directly, since the server will be automatically started by any function that will need it.
-spec stop() -> ok.
Equivalent to stop(normal)
.
-spec stop(Reason) -> ok when Reason :: term().
Stops the fprof
server.
The supplied Reason
becomes the exit reason for the server process. By default,
any Reason
other than kill
sends a request to the server and waits for it to
clean up, reply, and exit. If Reason
is kill
, the server is bluntly killed.
If the fprof
server is not running, this function returns immediately.
Note
When the
fprof
server is stopped the collected raw profile data is lost.
-spec trace(verbose) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when ServerPid :: pid(), Reason :: term(); (OptionName) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), ServerPid :: pid(), Reason :: term(); ({OptionName, OptionValue}) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term(); (OptionList) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionList :: [Option], Option :: trace_option(), ServerPid :: pid(), Reason :: term().
Starts or stops tracing.
If Arg
is atom verbose
, this call is equivalent to
trace([start, verbose])
.
If Arg
is an atom, this call is equivalent to
trace([Arg])
.
If Arg
is a tuple {OptionName, OptionValue}
, this call is equivalent to
trace([Arg])
.
Otherwise, Arg
has to be a list of trace options.
PidSpec
and Tracer
are used in calls to
erlang:trace(PidSpec, true, [{tracer, Tracer} | Flags])
,
and Filename
is used to call
dbg:trace_port(file, Filename)
.
Option description:
stop
- Stops a runningfprof
trace and clears all tracing from the node. Either optionstop
orstart
must be specified, but not both.start
- Clears all tracing from the node and starts a newfprof
trace. Either optionstart
orstop
must be specified, but not both.verbose
|{verbose, boolean()}
- Theverbose
or{verbose, true}
options add some trace flags thatfprof
does not need, but that can be interesting for general debugging purposes. These options are only allowed with thestart
option.cpu_time
|{cpu_time, boolean()}
- Thecpu_time
or{cpu_time, true}
options make the timestamps in the trace be in CPU time instead of the default wallclock time. These options are only allowed with thestart
option.Note
Getting correct values out of
cpu_time
can be difficult. The best way to get correct values is to run using a single scheduler and bind that scheduler to a specific CPU. For example:erl +S 1 +sbt db`
{procs, PidSpec}
|{procs, [PidSpec]}
- Specifies which processes that should be traced. If this option is not given, the calling process is traced. All processes spawned by the traced processes are also traced. This option is only allowed with thestart
option.file
|{file, Filename}
- Specifies the filename of the trace. If the optionfile
is given, or none of these options are given, the filefprof.trace
is used. This option is only allowed with thestart
option, but not with the{tracer, Tracer}
option.{tracer, Tracer}
- Specifies that trace to process or port shall be done instead of trace to file. This option is only allowed with thestart
option, but not with the{file, Filename}
option.
-spec trace(start, Filename) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when Filename :: file:filename(), ServerPid :: pid(), Reason :: term(); (verbose, Filename) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when Filename :: file:filename(), ServerPid :: pid(), Reason :: term(); (OptionName, OptionValue) -> ok | {error, Reason} | {'EXIT', ServerPid, Reason} when OptionName :: atom(), OptionValue :: term(), ServerPid :: pid(), Reason :: term().
Starts or stop tracing.
If What
is atom start
, this call is equivalent to
trace([start, {file, Value}])
.
If What
is atom verbose
, this call is equivalent to
trace([start, verbose, {file, Value}])
.
If What
is a tuple {OptionName, OptionValue}
,
this call is equivalent to
trace([What])
.