Golang implements taskset

Taskset is a commonly used Linux command used to specify CPU affinity, that is, determine which CPU a process runs on. It can limit processes to a specified set of CPUs by setting a mask. Processes running on multi-CPU machines often benefit from using tasksets to limit CPU affinity in order to optimize performance. In this article, we will introduce how to write a simple taskset command implementation using golang.

In order to realize the basic functions of taskset, we need to use some specific libraries and functions in golang. These libraries include os, flag and strconv. We will use the flag library to parse command line parameters, the os library to operate the operating system functions, and the strconv library to convert data types.

First, we need to define our command line parameters, which include the process ID and CPU mask to run. In golang, we can use the flag package to define command line options and parse them in the program:

import "flag"

var (
  processID int
  cpuMask   string
)

func init() {
  flag.IntVar(&processID, "p", 0, "pid to modify")
  flag.StringVar(&cpuMask, "c", "", "CPU affintiy mask (in hex)")
}

func main() {
  flag.Parse()
  // ...
}

Here, we define two variables processID and cpuMask. We use flag.IntVar and flag.StringVar to define these two variables, which correspond to the command line parameters "-p" and "-c" respectively. The meaning of these parameters is explained in the code comments.

Now we can handle the command line arguments and execute the taskset code as needed. We will use the sched_setaffinity function from the os library to set the CPU affinity. This function can be used on either a single process or a process group. In our example, we will use a single process ID to set CPU affinity.

import (
  "fmt"
  "syscall"
)

func setAffinity(pid int, mask string) error {
  if pid <= 0 {
    return fmt.Errorf("invalid PID %d", pid)
  }

  tid, err := syscall.Gettid()
  if err != nil {
    return fmt.Errorf("failed to get TID: %v", err)
  }

  var cpuSet syscall.CPUSet
  _, err = fmt.Sscanf(mask, "%x", &cpuSet)
  if err != nil {
    return fmt.Errorf("failed to scan CPU mask %s: %v", mask, err)
  }

  err = syscall.SchedSetaffinity(tid, &cpuSet)
  if err != nil {
    return fmt.Errorf("failed to set affinity: %v", err)
  }

  return nil
}

In this function, we first check whether the process ID is a valid value. Then, we use the syscall.Gettid function to get the thread ID. This ID will be used to set the CPU affinity in the SchedSetaffinity function. Next, we convert the passed CPU mask to the syscall.CPUSet type to pass to the SchedSetaffinity function. Finally, we check the return value of the SchedSetaffinity function and return any errors.

Now, we have completed writing the setAffinity function. Now, we need to handle the command line parameters and call the setAffinity function in the main function of the program.

func main() {
  flag.Parse()

  err := setAffinity(processID, cpuMask)
  if err != nil {
    fmt.Printf("Error: %v
", err)
  } else {
    fmt.Println("CPU affinity set successfully")
  }
}

In this function, we first use the flag.Parse function to parse the command line parameters. Then, we call the setAffinity function to set the CPU affinity. If the function returns an error, an error message is output to the console, otherwise a success message is output.

Now, we have successfully written a simple taskset program to set the CPU affinity of a process. When using this program, please remember that root privileges are required to run it.

To summarize, we wrote a simple taskset program using golang that can set the CPU affinity of a process. We used the flag package to implement command line parameter parsing, and used the os and syscall packages to perform actual tasks. This is a very useful tool for those who need to run programs in multi-CPU systems.

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