Operating Systems (CS 273 (OS), Fall 2020)

(Version 5.0.21)

Process table

Scheduler; context switching

The scheduler is called schedule(), defined in schedule.
sched_submit_work() updates Linux's bookkeeping to prevent I/O deadlocks if a process is becoming blocked. Deadlock means that there is a collection of processes, each blocked waiting for an event that can only be caused by another process in that collection. (Will study deadlocks later.)
__schedule performs more deadlock prevention (preemp_disable()) and some IPC operations ("read/copy/update" synchronization operation rcu_note_context_switch(), raw_spin_lock_irq(), etc.), then calls context_switch
- switch_to includes some of the register movements, saving from outgoing process and obtaining values for incoming process.
- Paravirtualization -- for making low-level tweaks of kernel for bare hardware vs. a virtual machine.
  arch_start_context_switch implemented using PVOP_VCALL1() macro, which is ultimately defined in terms of another macro ____PVOP_CALL implemented using assembly calls.
- Macro prepare_arch_switch - insures that a specific assembly-level computation doesn't get optimized away by compiler, by inserting an empty computation that won't be "crossed" by optimization rewriting.