性能工具之 C/C++ 分析工具 valgrind

一、前言

其实对 C/C++ 的应用来说，查看函数时间调用和内存消耗调用的有很多工具，valgrind 这个工具算是做得比较不错的一个。建议直接用 yum 安装，有的说可以安装更新的版本，像我这种不喜欢各种找依赖条件的，就直接 yum 了。

二、快速使用

1、查看内存越界和泄露的情况

它的使用也非常简单，比如下面这个例子，可以查看内存越界和泄露的情况。只要用 valgrind 调用一下被测试的程序即可。

memcheck：

[root@7dgroupSample10]# vi test5.c
[root@7dgroupSample10]# gcc -Wall -o test5 test5.c
[root@7dgroupSample10]# valgrind --tool=memcheck --leak-check=full ./test5
==318==Memcheck, a memory error detector
==318==Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==318==Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==318==Command: ./test5
==318==
==318== Invalid write of size 4 //内存越界
==318==    at 0x40054E: f (in/root/GDB/Sample10/test5)
==318==    by 0x40055E: main (in/root/GDB/Sample10/test5)
==318==  Address 0x51f7068 is 0bytes after a block of size 40 alloc'd
==318==    at 0x4C29BFD: malloc(in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==318=    by 0x400541: f (in/root/GDB/Sample10/test5)
==318=    by 0x40055E: main (in/root/GDB/Sample10/test5)
==318==
==318==
==318==HEAP SUMMARY:
==318==     in use at exit: 40 bytes in 1 blocks
==318==   total heap usage: 1 allocs, 0 frees, 40bytes allocated
==318==
==318== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 //内存泄露
==318==    at 0x4C29BFD: malloc(in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==318==    by 0x400541: f (in/root/GDB/Sample10/test5)
==318==    by 0x40055E: main (in/root/GDB/Sample10/test5)
==318==
==318==LEAK SUMMARY:
==318==    definitely lost: 40 bytes in 1 blocks
==318==    indirectly lost: 0 bytes in 0 blocks
==318==      possibly lost: 0 bytes in 0 blocks
==318==    still reachable: 0 bytes in 0 blocks
==318==         suppressed: 0 bytes in 0 blocks
==318==
==318==For counts of detected and suppressed errors, rerun with: -v
==318==ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 1 from 1)
[root@7dgroupSample10]#

2、查看引用次数，命中率等信息

再看一下它的其他工具：

cachegrind： Cache分析器，可以查看引用次数，命中率等信息。

[root@7dgroupSample10]# valgrind --tool=cachegrind ./test5
==1655==Cachegrind, a cache and branch-prediction profiler
==1655==Copyright (C) 2002-2013, and GNU GPL'd, by Nicholas Nethercote et al.
==1655==Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==1655==Command: ./test5
==1655==
--1655--warning: L3 cache found, using its data for the LL simulation.
--1655--warning: specified LL cache: line_size 64 assoc 20  total_size 31,457,280
--1655--warning: simulated LL cache: line_size 64 assoc 30  total_size 31,457,280
==1655==
==1655== I   refs:      152,928
==1655== I1  misses:        765
==1655== LLi misses:        759
==1655== I1  miss rate:    0.50%
==1655== LLi miss rate:    0.49%
==1655==
==1655== D   refs:       51,260 (39,547 rd   + 11,713 wr)
==1655== D1  misses:      2,861 ( 2,321 rd   +    540 wr)
==1655== LLd misses:     2,384  ( 1,891 rd   +   493 wr)
==1655== D1  miss rate:     5.5% (  5.8%     +    4.6% )
==1655== LLd miss rate:     4.6%(   4.7%     +   4.2%  )
==1655==
==1655== LL refs:        3,626  ( 3,086 rd   +   540 wr)
==1655== LL misses:      3,143  ( 2,650 rd   +   493 wr)
==1655== LL miss rate:      1.5%(   1.3%     +   4.2%  )
[root@7dgroupSample10]# 

3、查看函数调用关系及时间消耗

callgrind: 查看函数调用关系及时间消耗

[root@7dgroupSample10]# valgrind --tool=callgrind /usr/sbin/nginx
==1713==Callgrind, a call-graph generating cache profiler
==1713==Copyright (C) 2002-2013, and GNU GPL'd, by Josef Weidendorfer et al.
==1713==Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info
==1713==Command: /usr/sbin/nginx
==1713==
==1713==For interactive control, run 'callgrind_control -h'.
==1713==
==1713==Events    : Ir
==1713==Collected : 8916001
==1713==
==1713==I   refs:      8,916,001

[root@7dgroupSample10]# ll
总用量 884
-rw-------.1 root root   5047 4月  17 21:12 cachegrind.out.1655
-rw-------.1 root root 129128 4月  17 21:15callgrind.out.1702
-rw-------. 1 root root 128813 4月 17 21:16 callgrind.out.1713

这个结果可以生成调用图。

如下所示：

还可以用 kcachegrind（有 linux 和 windows 版本）打开 out 文件。

如下所示 ：

在这个图的下面还有一个百分比图例，直接双击可以一层层 drill down下去，直到一个具体的函数。也可以直接看到相应的源码（前提是有 ELF 文件）。

三、总结

这个工具有它的局限性，就是它不能 attach 进程。如果要查看运行中的进程的内存消耗和函数消耗情况，可以使用其他工具。有感兴趣的以后我再写如何查看运行中的C/C++剖析工具。
这是个对 C/C++ 进程的工具。java 的工具就更多了，以后再整理。

工具用好了事半功倍，但是前提是理解原理。