In Linux, CPU affinity is a powerful feature that allows you to bind or unbind a process or a thread to a specific Central Processing Unit (CPU) or a range of CPUs. By managing CPU affinity, you can optimize system performance, especially in multi-core processors, by ensuring that certain processes run on specific CPUs. This can help reduce cache misses and improve the performance of CPU-bound applications.

Examples:

1. Using taskset to Set CPU Affinity:

   The taskset command in Linux is used to set or retrieve the CPU affinity of a running process. You can also use it to launch a new command with a specific CPU affinity.

   • Set CPU Affinity for a New Process:

     To start a new process with a specific CPU affinity, use the following syntax:

     taskset -c 0,2 my_command

     This command will run my_command on CPUs 0 and 2.

   • Set CPU Affinity for an Existing Process:

     To change the CPU affinity of an existing process, use the process ID (PID):

     taskset -cp 0-3 1234

     This command will set the CPU affinity of the process with PID 1234 to CPUs 0, 1, 2, and 3.

   • Retrieve CPU Affinity:

     To check the current CPU affinity of a process, use:

     taskset -cp 1234

     This will display the CPUs on which the process with PID 1234 is allowed to run.

2. Using sched_setaffinity System Call:

   For more advanced use cases, you can use the sched_setaffinity system call in a C program to set the CPU affinity of a process programmatically.

   • Example C Program:

     #define _GNU_SOURCE
     #include <sched.h>
     #include <stdio.h>
     #include <unistd.h>
     
     int main() {
      cpu_set_t mask;
      CPU_ZERO(&mask);
      CPU_SET(0, &mask);
     
      pid_t pid = getpid();
      if (sched_setaffinity(pid, sizeof(mask), &mask) == -1) {
          perror("sched_setaffinity");
          return 1;
      }
     
      // Your code here
      printf("Process running on CPU 0\n");
      while (1); // Keep the process running to observe CPU affinity
     }

     This program sets the CPU affinity of itself to CPU 0.

3. Using cset (CPUSET) for More Complex Scenarios:

   cset is a tool that allows for more complex CPU affinity configurations, including isolating CPUs for specific tasks.

   • Install cset:

     sudo apt-get install cpuset

   • Create a CPUSET:

     sudo cset set --cpu 0,1 --set=myset

     This creates a CPUSET named myset that includes CPUs 0 and 1.

   • Move a Process to a CPUSET:

     sudo cset proc --set=myset --exec my_command

     This moves my_command to run within the myset CPUSET.

   • List CPUSETs:

     cset set --list

     This command lists all available CPUSETs and their configurations.

By using these tools, you can effectively manage CPU affinity in Linux, optimizing the performance of your applications and making the most of your system's resources.