4 ms·

I was curious, so, here goes; 'foo' was a file of ~1G containing lines made up of of 999 'x's and one '\n'. $ ls -lh foo -rw-r--r-- 1 ori ori 954M Sep

by ori_b 14y ago

I was curious, so, here goes; 'foo' was a file of ~1G containing lines made up of of 999 'x's and one '\n'. $ ls -lh foo -rw-r--r-- 1 ori ori 954M Sep 5 22:57 foo $ time cat foo | awk '{print $1}' > /dev/null real 0m1.631s user 0m1.452s sys 0m0.540s $ time awk <foo '{print $1}' > /dev/null real 0m1.541s user 0m1.376s sys 0m0.160s This was run from a warm cache, so that the overhead of the extra IO from a pipe would dominate.

dustyleary 14y ago
Both invocations take similiar amounts of "real" time because the task is IO-bound and it takes roughly 1.5s on your machine to read the file. But if you add up the "user" and "sys" time in the cat example, you see that it took 1.992s of actual cpu-time... Which is actually about a 30% increase in cpu-time spent. The perf decrease wasn't visible because you have multiple cores parallelizing the extra cpu-time, but it was there.