Does linux schedule a process or a thread?

by

The Linux scheduler (on recent Linux kernels, e.g. 3.0 at least) is scheduling schedulable tasks or simply tasks.

A task may be :

  • a single-threaded process (e.g. created by fork without any thread library)
  • any thread inside a multi-threaded process (including its main thread), in particular Posix threads (pthreads)
  • kernel tasks, which are started internally in the kernel and stay in kernel land (e.g. kworker, nfsiod, kjournald , kauditd, kswapd etc etc…)

In other words, threads inside multi-threaded processes are scheduled like non-threaded -i.e. single threaded- processes.

The low-level clone(2) syscall creates user-land schedulable tasks (and can be used both for creating fork-ed process or for implementation of thread libraries, like pthread). Unless you are a low-level thread library implementor, you don’t want to use clone directly.

AFAIK, for multi-threaded processes, the kernel is (almost) not scheduling the process, but each individual thread inside (including the main thread).

Actually, there is some notion of thread groups and affinity in the scheduling, but I don’t know them well

These days, processors have generally more than one core, and each core is running a task (at some given instant) so you do have several tasks running in parallel.

CPU quantum times are given to tasks, not to processes

More Related Contents:

  1. How Linux handles threads and process scheduling
  2. Threads vs Processes in Linux [closed]
  3. Maximum number of threads per process in Linux?
  4. How can I measure the actual memory usage of an application or process?
  5. What’s the best way to send a signal to all members of a process group?
  6. How to prevent a background process from being stopped after closing SSH client in Linux
  7. What killed my process and why?
  8. How do I set the working directory of the parent process?
  9. What is an uninterruptible process?
  10. Maximum number of processes in linux [closed]
  11. How to instruct cron to execute a job every second week?
  12. When should we use mutex and when should we use semaphore
  13. Is it safe to fork from within a thread?
  14. Modify Qt GUI from background worker thread
  15. How do I programmatically disable hardware prefetching?
  16. How to write data to existing process’s STDIN from external process?
  17. How does Linux determine the next PID?
  18. Programmatically get parent pid of another process?
  19. Linux/Unix command to determine if process is running?
  20. How to get child process from parent process
  21. How can I programmatically manage iptables rules on the fly?
  22. What are the thread limitations when working on Linux compared to processes for network/IO-bound apps?
  23. How do I get the path of a process in Unix / Linux?
  24. Multithreading in Bash [duplicate]
  25. What is path //, how is it different from /
  26. prevent linux thread from being interrupted by scheduler
  27. kernel symbol marked with “T” in /proc/kallsyms is not exported
  28. Start script after another one (already running) finishes
  29. How to set process group of a shell script
  30. How to set process ID in Linux for a specific program

Leave a Comment