英文:
Pprof and golang - how to interpret a results?
问题
我正在尝试在我的程序中使用pprof，但是我得到的结果与我阅读的文章（下面的链接）略有不同。在我的结果中，我得到了这样的表格：
(pprof) top10
1.65秒占总时间的1.72秒（95.93%）
显示114个节点中的前10个（累积时间 >= 0.01秒）
flat flat% sum% cum cum%
1.19秒 69.19% 69.19% 1.20秒 69.77% syscall.Syscall
0.16秒 9.30% 78.49% 0.16秒 9.30% runtime._ExternalCode
这些列代表什么意思：flat flat% sum% cum cum%？
我正在阅读的文章：
https://software.intel.com/en-us/blogs/2014/05/10/debugging-performance-issues-in-go-programs
http://blog.golang.org/profiling-go-programs
英文:
I am trying to use pprof on my program, however, I have slightly different results from articles I read (links below). In my results, I am getting such table:
(pprof) top10
1.65s of 1.72s total (95.93%)
Showing top 10 nodes out of 114 (cum >= 0.01s)
flat flat% sum% cum cum%
1.19s 69.19% 69.19% 1.20s 69.77% syscall.Syscall
0.16s 9.30% 78.49% 0.16s 9.30% runtime._ExternalCode
what are this columns: flat flat% sum% cum cum%?
Articles I was reading:
https://software.intel.com/en-us/blogs/2014/05/10/debugging-performance-issues-in-go-programs
http://blog.golang.org/profiling-go-programs
答案1
得分: 40
flat 和 cum
假设有一个名为 foo 的函数，它由 3 个函数和一个直接操作组成。
func foo(){
a() // 步骤1
b() // 步骤2
直接执行某些操作 // 步骤3
c() // 步骤4
}
假设当你调用函数 foo 时，它需要 6 秒钟，并且时间分布如下：
func foo(){
a() // 步骤1 耗时 1 秒
b() // 步骤2 耗时 1 秒
直接执行某些操作 // 步骤3 耗时 3 秒
c() // 步骤4 耗时 1 秒
}
flat表示步骤3所花费的时间。cum表示 foo 的总执行时间，包括子函数调用和直接操作。（cum = 步骤1 + 步骤2 + 步骤3 + 步骤4）
sum%
当你在 pprof 控制台中运行 top 命令时，每行输出代表特定函数所花费的时间。Sum% 表示前面几行所花费的时间或内存的总和。
为了解释这个指标，我选择了另一个包含更多行的示例。第四行的 sum% 值为 45.17%。计算方法如下：
line1 19.33%
line2 13.27%
line3 6.60%
line4 5.97%
-----------
sum% 45.17%
sum% 的应用
sum% 可以帮助你快速识别主要问题。下面是另一个内存分配报告的示例。
你可以看到前四个函数占用了 91.06% 的内存。如果我想进行性能调优，应该集中关注前四个函数，而可以忽略第四个函数以下的所有函数。
参考资料
Reddit: What is the meaning of "flat" and "cum" in golang pprof output
英文:
flat and cum
Assuming there is a function foo, which is composed of 3 functions and a direct operation.
func foo(){
a() step1
b() step2
do something directly. step3
c() step4
}
Imagine when you call function foo, it takes 6 seconds, and the time distribution are following.
func foo(){
a() // step1 takes 1s
b() // step2 takes 1s
do something directly. // step3 takes 3s
c() // step4 takes 1s
}
flatwould be the time spent on step3.cumwould be the total execution time of foo, which contains sub-function call and direct operations. (cum = step1+ step2+ step3+ step4)
sum%
when you run top in pprof console, each line of output stands for the time spent on specific function. Sum% means how much time/memory has been spent by previous lines.
To explain this metric, I pick another example which contains more lines. the value of sum% for forth line is 45.17%. it's the calculated in this way:
line1 19.33%
line2 13.27%
line3 6.60%
line4 5.97%
-----------
sum% 45.17%
Application of sum%
sum% could help you to identify the big rocks quickly. The following is another example of memory allocation report.
You can see that the first four functions consume 91.06% memory. If I want to do some performance tuning, I should focus on first four functions. All the functions below fourth could be ignored.
Reference
Reddit: What is the meaning of "flat" and "cum" in golang pprof output
答案2
得分: 2
我知道我会因为这个而受到指责，但是看一下GopherCon的演讲吧；这里有一个关于解释的例子，还有一场来自Uber关于pprof的演讲。
还有一篇关于Go程序性能分析的博文。
英文:
I know I'm going to get flack for this, but take a look at the GopherCon talks; one such example on interpretation is here, there is also a talk from Uber about pprof as well.
There is also Profiling Go Programs blog post.
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