[转贴]gprof使用备忘

gprof介绍
gprof是GNU profiler工具。可以显示程序运行的“flatprofile”，包括每个函数的调用次数，每个函数消耗的处理器时间。也可以显示“调用图”，包括函数的调用关系，每个函数调用花费了多少时间。还可以显示“注释的源代码”，是程序源代码的一个复本，标记有程序中每行代码的执行次数。

为gprof编译程序
在编译或链接源程序的时候在编译器的命令行参数中加入“-pg”选项，编译时编译器会自动在目标代码中插入用于性能测试的代码片断，这些代码在程序在运行时采集并记录函数的调用关系和调用次数，以及采集并记录函数自身执行时间和子函数的调用时间，程序运行结束后，会在程序退出的路径下生成一个gmon.out文件。这个文件就是记录并保存下来的监控数据。可以通过命令行方式的gprof或图形化的Kprof来解读这些数据并对程序的性能进行分析。另外，如果想查看库函数的profiling，需要在编译是再加入“-lc_p”编译参数代替“-lc”编译参数，这样程序会链接libc_p.a库，才可以产生库函数的profiling信息。如果想执行一行一行的profiling，还需要加入“-g”编译参数。
例如如下命令行：
gcc -Wall -g -pg -lc_p example.c -oexample

执行gprof
执行如下命令行，即可执行gprof：
gprof OPTIONS EXECUTABLE-FILE gmon.outBB-DATA [YET-MORE-PROFILE-DATA-FILES...] [>OUTFILE]

gprof产生的信息
 

%                                              the percentage of the total running time of the
time                                        program used by this function.
                                                  函数使用时间占所有时间的百分比。
cumulative                  a running sum of the number of seconds accounted
  seconds                        for by this function and those listed above it.
                                                  函数和上列函数累计执行的时间。
  self                                      the number of seconds accounted for by this
seconds                        function alone.  This is the major sort forthis
                                                  listing.
                                                函数本身所执行的时间。
calls                                    the number of times this function was invoked, if
                                                  this function is profiled, else blank.
                                                函数被调用的次数
  self                                    the average number of milliseconds spent in this
ms/call                            function per call, if this function is profiled,
                                              else blank.
                                                每一次调用花费在函数的时间microseconds。
  total                                  the average number of milliseconds spent in this
ms/call                            function and its descendents per call, if this
                                                function is profiled, else blank.
                                                每一次调用，花费在函数及其衍生函数的平均时间microseconds。
name                                the name of the function.  This is the minorsort
                                                  for this listing. The index shows the location of
                                                the function in the gprof listing. If the index is
                                                in parenthesis it shows where it would appear in
                                                the gprof listing if it were to be printed.
                                                函数名

 

gprof对于profiling非常有用，不过初学者可能会遇到一些障碍。下面把步骤一一列出，应该比较容易明白了。

$ uname -a
Linux dev 2.4.21-9.30AXsmp #1 SMP Wed May 26 23:37:09 EDT 2004 i686i686 i386 GNU/Linux

$ gprof --version
GNU gprof 2.14.90.0.4
Based on BSD gprof, copyright 1983 Regents of the University ofCalifornia.
This program is free software. This program has absolutely nowarranty.

$ cat foo.c

int main(void)
{
    printf("helloworld/n");
    return0;
}

$ gcc -g -pg foo.c

$ ./a.out
hello world

$ gprof
gprof: gmon.out file is missing call-graphdata

    这个结果有点莫名其妙。难道这个简单的一个例子都过不了？其实这是gprof的一个“feature”，也许是专门用来迷惑初学者的。出错的原因参见：http://gcc.gnu.org/ml/gcc-help/2006-06/msg00037.html，是我们的函数过于简单，其中没有什么函数调用导致的。

    让我们换个复杂一点的例子看看。

$ cat bar.c

static int sub(void);

int main(void)
{
    inti;

    printf("helloworld/n");

    for(i = 0; i < 10; i++)
        sub();

    return0;
}

static int sub(void)
{
    return0;
}

$ gcc -g -pg bar.c
$ ./a.out
hello world

    注意这次输出的信息正常了，不过显得有点罗嗦。后面我们将采用“gprof-b”简化之。命令“gprof”其实就是“gprof a.out gmon.out”。

$ gprof
Flat profile:

Each sample counts as 0.01 seconds.
no time accumulated

% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 10 0.00 0.00 sub

% the percentage of the total running time of the
time program used by this function.

cumulative a running sum of the number of secondsaccounted
seconds for by this function and those listed above it.

self the number of seconds accounted for by this
seconds function alone. This is the major sort for this
listing.

calls the number of times this function was invoked, if
this function is profiled, else blank.

self the average number of milliseconds spent in this
ms/call function per call, if this function is profiled,
else blank.

total the average number of milliseconds spent in this
ms/call function and its descendents per call, if this
function is profiled, else blank.

name the name of the function. This is the minor sort
for this listing. The index shows the location of
the function in the gprof listing. If the index is
in parenthesis it shows where it would appear in
the gprof listing if it were to be printed.

Call graph (explanation follows)

granularity: each sample hit covers 4 byte(s) no timepropagated

index % time self children called name
0.00 0.00 10/10 main [8]
[1] 0.0 0.00 0.00 10 sub [1]
-----------------------------------------------

This table describes the call tree of the program, and wassorted by
the total amount of time spent in each function and itschildren.

Each entry in this table consists of several lines. The linewith the
index number at the left hand margin lists the currentfunction.
The lines above it list the functions that called thisfunction,
and the lines below it list the functions this one called.
This line lists:
index A unique number given to each element of the table.
Index numbers are sorted numerically.
The index number is printed next to every function name so
it is easier to look up where the function in the table.

% time This is the percentage of the `total' time that wasspent
in this function and its children. Note that due to
different viewpoints, functions excluded by options, etc,
these numbers will NOT add up to 100%.

self This is the total amount of time spent in thisfunction.

children This is the total amount of time propagated intothis
function by its children.

called This is the number of times the function wascalled.
If the function called itself recursively, the number
only includes non-recursive calls, and is followed by
a `+' and the number of recursive calls.

name The name of the current function. The index number is
printed after it. If the function is a member of a
cycle, the cycle number is printed between the
function's name and the index number.

For the function's parents, the fields have the followingmeanings:

self This is the amount of time that was propagateddirectly
from the function into this parent.

children This is the amount of time that was propagatedfrom
the function's children into this parent.

called This is the number of times this parent called the
function `/' the total number of times the function
was called. Recursive calls to the function are not
included in the number after the `/'.

name This is the name of the parent. The parent's index
number is printed after it. If the parent is a
member of a cycle, the cycle number is printed between
the name and the index number.

If the parents of the function cannot be determined, theword
`<spontaneous>' is printed in the `name' field, and all theother
fields are blank.

For the function's children, the fields have the followingmeanings:

self This is the amount of time that was propagateddirectly
from the child into the function.

children This is the amount of time that was propagated fromthe
child's children to the function.

called This is the number of times the function called
this child `/' the total number of times the child
was called. Recursive calls by the child are not
listed in the number after the `/'.

name This is the name of the child. The child's index
number is printed after it. If the child is a
member of a cycle, the cycle number is printed
between the name and the index number.

If there are any cycles (circles) in the call graph, there isan
entry for the cycle-as-a-whole. This entry shows who calledthe
cycle (as parents) and the members of the cycle (aschildren.)
The `+' recursive calls entry shows the number of function callsthat
were internal to the cycle, and the calls entry for each membershows,
for that member, how many times it was called from other membersof
the cycle.

 

Index by function name

[1] sub (bar.c)

$ gprof -b
Flat profile:

Each sample counts as 0.01 seconds.
no time accumulated

% cumulative self self total
time seconds seconds calls Ts/call Ts/call name
0.00 0.00 0.00 10 0.00 0.00 sub

Call graph

granularity: each sample hit covers 4 byte(s) no timepropagated

index % time self children called name
0.00 0.00 10/10 main [8]
[1] 0.0 0.00 0.00 10 sub [1]
-----------------------------------------------

Index by function name

[1] sub (bar.c)

   gprof的这个特性很容易让初学者迷惑，可能一上来就把人吓跑了。我们再写个复杂一点点的例子，应该更容易看出gprof的用处了。

$cat bar.c

static int sub(void);
static int sub2(void);

int main(void)
{
    sub();
    sub2();

    return0;
}

static int sub(void)
{
    inti;
    intres = 0;

    for(i = 0; i < 10000000; i++)
        res+= i;

    returnres;
}

static int sub2(void)
{
    inti;
    intres = 0;

    for(i = 0; i < 10000000; i++)
        res*= i;

    returnres;
}

$gcc -g -pg bar.c

$./a.out

$gprof -b
Flat profile:

Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
53.33 0.08 0.08 1 80.00 80.00sub2
46.67 0.15 0.07 1 70.00 70.00sub

Call graph

granularity: each sample hit covers 4 byte(s) for 6.67% of 0.15seconds

index % time self children called name
<spontaneous>
[1] 100.0 0.00 0.15 main [1]
0.08 0.00 1/1 sub2 [2]
0.07 0.00 1/1 sub [3]
-----------------------------------------------
0.08 0.00 1/1 main [1]
[2] 53.3 0.08 0.00 1 sub2 [2]
-----------------------------------------------
0.07 0.00 1/1 main [1]
[3] 46.7 0.07 0.00 1 sub [3]
-----------------------------------------------

Index by function name

[3] sub (bar.c) [2] sub2 (bar.c)