cpu time区分

时间区分

1. wall-clock time(or real time)
   指的就是现实当中时钟走的的时间
2. user cpu time
   指user code运行消耗的cpu时间
3. system cpu time
   指system code运行消耗的cpu时间
   如系统执行read, write等I/O的时间

几个结论

1. wall time < cpu time
   说明程序进行了并行操作
2. wall time > cpu time
   说明发生了磁盘读写，网络传输的等待延迟

测试

#!/bin/bash
# sum.sh
sum=0

for i in {1..10000}
do
  let sum=$sum+$i
done
echo "Sum of range from 1 to 10000 is: $sum"

chmod u+x sum.sh
time ./sum.sh

参考https://stackoverflow.com/questions/7335920/what-specifically-are-wall-clock-time-user-cpu-time-and-system-cpu-time-in-uni