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 `' 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 [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)
