Systemtap examples, Profiling - 1 Counting Function Calls Made

背景

接下来开始对systemtap example的另一个分类Profiling做一些例子的讲解.  
例子来自functioncallcount.stp 脚本, 该脚本通过函数的调用情况分析内核活动. 由于没有终止时间, 同时使用统计类型性能不如数组自增, 所以我做了相应的修改. (但是请注意数组以及全局标量自增是需要锁的, 所以在多CPU(SMP)的系统中并行的自增会带来一定问题.而统计类型不会有这个问题)  
修改后的脚本内容以及注解 :   
[root@db-172-16-3-150 network]# cd /usr/share/systemtap/testsuite/systemtap.examples/profiling  
[root@db-172-16-3-150 profiling]# cat functioncallcount.stp  
#!/usr/bin/stap  
# The following line command will probe all the functions  
# in kernel's memory management code:  
#  
# stap  functioncallcount.stp "*@mm/*.c"  
  
probe kernel.function(@1).call {  # probe functions listed on commandline  
  # called[probefunc()] <<< 1  # add a count efficiently  
  called[probefunc()]++  
// 这里当然可以不使用统计类型, 使用数组自增就可以了.   
// 数组在这里的性能比使用统计类型要好  
}  
// 第一个stap命令行传入参数为字符串, 指定函数或函数通配符  
// 注意尽量不要使用*, 如果匹配的函数太多, 可能会导致操作系统无响应.  
  
global called  
  
// 最好限定一个统计时间, 否则需要等用户来退出这个模块.   
// 这里相当于10秒后退出.  
probe timer.s(10) {  
  exit()  
}  
  
probe end {  
  foreach (fn in called- limit 10)  # Sort by call count (in decreasing order)  
  #       (fn+ in called)  # Sort by function name  
    #printf("%s %d\n", fn, @count(called[fn]))  
    printf("%s %d\n", fn, called[fn])  
  exit()  
}  
// end事件触发时, 输出调用次数排名前10的函数名以及调用次数.  
// 或者按照函数名来排序. 输出所有的函数以及调用次数.  
  
执行输出举例 :   
[root@db-172-16-3-150 profiling]# stap functioncallcount.stp "*@mm/*.c"  
kfree 271266  
__phys_addr 187769  
kmem_cache_free 156818  
__inc_zone_state 122738  
kmem_cache_alloc 109292  
page_waitqueue 96884  
lookup_page_cgroup 79088  
kmem_cache_alloc_node 70086  
__kmalloc_node 70056  
kmem_cache_alloc_node_trace 70056  
  
本文用到的几个函数 :   

https://sourceware.org/systemtap/tapsets/API-probefunc.html

Name  
    function::probefunc — Return the probe point's function name, if known  
Synopsis  
    probefunc:string()  
Arguments  
    None  
Description  
    This function returns the name of the function being probed   
    based on the current address, as computed by symname(addr)  
    or usymname(uaddr) depending on probe context (whether the  
    probe is a user probe or a kernel probe).  
Please note  
    this function's behaviour differs between SystemTap   
    2.0 and earlier versions. Prior to 2.0, probefunc   
    obtained the function name from the probe point   
    string as returned by pp, and used the current   
    address as a fallback.  

参考

1. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/mainsect-profiling.html

2. https://sourceware.org/systemtap/examples/

3. /usr/share/systemtap/testsuite/systemtap.examples

4. systemtap-testsuite

5. /usr/share/systemtap/testsuite/systemtap.examples/index.txt

6. /usr/share/systemtap/testsuite/systemtap.examples/keyword-index.txt

7. /usr/share/systemtap/tapset

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