程序性能分析gropf工具

性能调优第一步是性能分析：
1、性能分析的目的：
　　1）找出系统性能瓶颈（包括硬件瓶颈和软件瓶颈）；
　　2）提供性能优化的方案（升级硬件？改进系统系统结构？）；
　　3）达到合理的硬件和软件配置；
　　4）使系统资源使用达到最大的平衡。（一般情况下系统良好运行的时候恰恰各项资源达到了一个平衡体，任何一项资源的过渡使用都会造成平衡体系破坏，从而造成系统负载极高或者响应迟缓。比如CPU过渡使用会造成大量进程等待CPU资源，系统响应变慢，等待会造成进程数增加，进程增加又会造成内存使用增加，内存耗尽又会造成虚拟内存使用，使用虚拟内存又会造成磁盘IO增加和CPU开销增加）

gropf工具：

1、原理
只要在编译时加上-pg选项，编译器就会在编译程序时在每个函数开头加上mcount函数调用
在每一个函数调用之前都会先调用这个mcount函数，在mcount中会保存函数的调用关系图和函数的调用时间和被调次数等信息。最终在程序退出时保存在gmon.out文件中，需要注意的是程序必须是正常退出或者通过exit调用退出，因为只要在exit（）被调用时才会触发程序写gmon.out文件
那么，gprof的使用方法主要以下三步：
会用-pg参数编译程序
运行程序，并正常退出
查看gmon.out文件

Flat profile:

Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
50.00 0.06 0.06 2 30.00 30.00 f()
25.00 0.09 0.03 1 30.00 60.00 g()
25.00 0.12 0.03 main
0.00 0.12 0.00 1 0.00 0.00 _GLOBAL__sub_I__Z1fv
0.00 0.12 0.00 1 0.00 0.00 __static_initialization_and_destruction_0(int, int)

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

cumulative a running sum of the number of seconds accounted
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.

Copyright (C) 2012-2016 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.

Call graph (explanation follows)

granularity: each sample hit covers 4 byte(s) for 8.33% of 0.12 seconds

index % time self children called name
<spontaneous>
[1] 100.0 0.03 0.09 main [1]
0.03 0.03 1/1 g() [3]
0.03 0.00 1/2 f() [2]
-----------------------------------------------
0.03 0.00 1/2 g() [3]
0.03 0.00 1/2 main [1]
[2] 50.0 0.06 0.00 2 f() [2]
-----------------------------------------------
0.03 0.03 1/1 main [1]
[3] 50.0 0.03 0.03 1 g() [3]
0.03 0.00 1/2 f() [2]
-----------------------------------------------
0.00 0.00 1/1 __libc_csu_init [17]
[8] 0.0 0.00 0.00 1 _GLOBAL__sub_I__Z1fv [8]
0.00 0.00 1/1 __static_initialization_and_destruction_0(int, int) [9]
-----------------------------------------------
0.00 0.00 1/1 _GLOBAL__sub_I__Z1fv [8]
[9] 0.0 0.00 0.00 1 __static_initialization_and_destruction_0(int, int) [9]
-----------------------------------------------

This table describes the call tree of the program, and was sorted by
the total amount of time spent in each function and its children.

Each entry in this table consists of several lines. The line with the
index number at the left hand margin lists the current function.
The lines above it list the functions that called this function,
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 is in the table.

% time This is the percentage of the `total' time that was spent
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 this function.

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

called This is the number of times the function was called.
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 following meanings:

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

children This is the amount of time that was propagated from
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, the word
`<spontaneous>' is printed in the `name' field, and all the other
fields are blank.

For the function's children, the fields have the following meanings:

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

children This is the amount of time that was propagated from the
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 is an
entry for the cycle-as-a-whole. This entry shows who called the
cycle (as parents) and the members of the cycle (as children.)
The `+' recursive calls entry shows the number of function calls that
were internal to the cycle, and the calls entry for each member shows,
for that member, how many times it was called from other members of
the cycle.

Copyright (C) 2012-2016 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.