问题描述
根据time()，我在使用16.637s的C ++程序上运行gprof，这是我在第一行输出中得到的:
I ran gprof on a C++ program that took 16.637s, according to time(), and I got this for the first line of output:
% cumulative self self total
time seconds seconds calls s/call s/call name
31.07 0.32 0.32 5498021 0.00 0.00 [whatever]
为什么只用了.32秒就列出了31.07%时间?这是每个通话时间吗? (那不是自我吗?)
Why does it list 31.07% of time if it only took .32 seconds? Is this a per-call time? (Wouldn't that be self s/call?)
这是我第一次使用gprof，请好心:)
This is my first time using gprof, so please be kind :)
通过向下滚动，看来gprof仅认为我的程序需要1.03秒.为什么会这么错呢?
by scrolling down, it appears that gprof only thinks my program takes 1.03 seconds. Why might it be getting it so wrong?
推荐答案
瓶颈在文件I/O中(请参阅).我切换到在缓冲区中读取整个文件，并且极大地加快了速度.
The bottleneck turned out to be in file I/O (see Is std::ifstream significantly slower than FILE?). I switched to reading the entire file in a buffer and it sped up enormously.
这里的问题是，在等待文件I/O时，gprof似乎无法生成准确的配置文件(请参见 http://www.regatta.cs.msu.su/doc/usr/share/man/info/ru_RU/a_doc_lib/cmds/aixcmds2/gprof.htm ).实际上，seekg和tellg甚至不在分析列表中，它们是瓶颈！
The problem here was that gprof doesn't appear to generate accurate profiling when waiting for file I/O (see http://www.regatta.cs.msu.su/doc/usr/share/man/info/ru_RU/a_doc_lib/cmds/aixcmds2/gprof.htm). In fact, seekg and tellg were not even on the profiling list, and they were the bottleneck!
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