Comment 7 for bug 1919154

The attached test code is borrowed from Jay, it measures the average time for running getpid() 100000000 times to see if NO_HZ_FULL will cause any performance degradation for context switch when it’s built into kernel

There are 4 test scopes:
1. Without NO_HZ_FULL built-in
the default value of NO_HZ is NO_HZ_IDLE in ubuntu kernel
2. With NO_HZ_FULL built-in, but not activate it in kernel cmdline
3. With NO_HZ_FULL built-in, and activate nohz_full on some CPUs (also isolcpu and rcu_nocbs) in kernel cmdline
4. With NO_HZ_FULL built-in, and activate nohz_full on some CPUs, but run test program on a non-activate nohz_full CPU

For the first 3 test scopes above also contain two test cases
1. Not pin the test program
2. Pin the test program to a specific CPU, in my test, it’s pinned to CPU 4 as below
taskset --cpu-list 4 ./test

For the forth test scope, only pin the test program to a specific CPU which is not in nohz_full