Overview

Process NICE priority values range from -20 to 19. ( see top NI column )
NI is the nice value, which is a user-space concept. PR is the process’s actual priority, as viewed by the Linux kernel.

For normal processes, the kernel priority is simply +20 from the nice value. Thus a process with the neutral nice value of zero has a kernel priority of 20. This offset-by-20 is done so that a process with a nice value of -20, the highest priority nice value, receives a kernel priority of zero. Lower numeric values equal higher scheduling priority.
For realtime processes, the kernel priority is the process’s real-time priority, but the PR column will simply print RT.

A process with the nice value of -20 is considered to be on top of the priority. And a process with nice value of 19 is considered to be low on the priority list.Using renice and taskset to manager a Linux process

Using renice and taskset to manage a Linux process

Display CPU Affinity for LGWR process and change CPU affinity to CPU 5

$ ps -elf | egrep 'NI|ora_lgwr' |  grep -v grep
F S UID        PID  PPID  C PRI  NI ADDR SZ WCHAN  STIME TTY          TIME CMD
0 S oracle    5825     1  0  60 -20 - 394456 semtim 13:25 ?       00:00:24 ora_lgwr_grac41

$ taskset -pc 5 5825
pid 5825's current affinity list: 0-7
pid 5825's new affinity list: 5

Monitor CPU affinity with top 
# top -H -p 5825 [  --> Press f --> Press j to add CPU affinity col ]
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  P COMMAND                                                              
 5825 oracle    20   0 1540m  32m  28m S  0.0  0.8   0:24.62 5 oracle             
--> P shows the CPU affinity which is 5 !

Compile a load program and and set affinity to CPU 5 during program start 
$ cc sq.c -o sq -lm
$ taskset -c 5 sq
$ sp
PID: 15949

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  P COMMAND                                                              
15949 oracle    20   0  6544  312  244 R 73.7  0.0   1:50.17 5 sq                                                                   
 5825 oracle    20   0 1540m  32m  28m S  0.0  0.8   0:25.10 5 oracle     

Increase the priority of a process and monitor this process
# renice -15 15949

# top -H -p 15949 [  --> Press f --> Press j to add CPU affinity col ]
Cpu(s):  9.5%us,  3.1%sy,  0.0%ni, 87.2%id,  0.1%wa,  0.0%hi,  0.2%si,  0.0%st

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  P COMMAND                                                              
15949 oracle     5 -15  6544  308  244 R 70.9  0.0  38:43.36 5 sq                                                                   
 5825 oracle    20   0 1540m  33m  29m S  0.0  0.8   1:20.49 5 oracle