The Linux Kernel/Processing

Processing: from process to CPU

Processes and Tasks

Process is a running user space program. Kernel can start a process with function do_execve. Processes occupy system resources, like memory, CPU time. System calls sys_fork and sys_execve are used to create new processes from user space. The process exit with an sys_exit system call.

How are the process handled within the kernel?

TODO

What are kernel threads?

TODO

How are kernel threads handled ?

TODO

• API: kthread_run,do_fork,do_execve,

• Implementation: current, task_struct

• ULK3 Chapter 3. Processes
• ULK3 Chapter 4. Interrupts and Exceptions
• ULK3 Chapter 5. Kernel Synchronization
• ULK3 Chapter 6. Timing Measurements
• ULK3 Chapter 7. Process Scheduling
• cat /proc/self/
• http://www.tldp.org/LDP/tlk/kernel/processes.html
• http://www.tldp.org/HOWTO/KernelAnalysis-HOWTO-6.html

Synchronization

• completion - use completion for synchronization task with ISR and task or two tasks.
  • #include <linux/completion.h>
  • LKD2: Completion Variables

• • LWN: completion events

• mutex
  • has owner and usage constrains
  • more easy to debug then semaphore
  • #include <linux/mutex.h>
• spinlock_t, timer_list, wait_queue_head_t
• semaphore - use mutex instead semaphore if possible
  • #include <include/linux/semaphore.h>
• atomic operations
  • #include <asm-generic/atomic.h>
  • atomic_dec_and_test
  • LKD2: Atomic Operations

• LKD2: Chapter 9. Kernel Synchronization Methods
• LDD3:Concurrency and Race Conditions
• http://www.tldp.org/LDP/tlk/kernel/kernel.html
• http://www.tldp.org/LDP/lki/lki-2.html

Time and Timers

• jiffies, irq0, timer_interrupt, do_timer_interrupt,

• LDD3:Time, Delays, and Deferred Work
• http://www.xml.com/ldd/chapter/book/ch06.html

Interrupts

• /proc/interrupts
• http://www.tldp.org/LDP/tlk/dd/interrupts.html
• LDD3:Interrupt Handling
• http://www.xml.com/ldd/chapter/book/ch09.html

Bottom Halves

• tasklet is a softirq, runs in interrupt context, for time critical operations
  • API: DECLARE_TASKLET, tasklet_schedule
  • implemented with tasklet_struct, HI_SOFTIRQ, TASKLET_SOFTIRQ

• workqueue - works in scheduler context, for delayed operation
  • API: DECLARE_WORK, schedule_work

• softirq is internal system facility and should not be used directly. Use tasklet.

• http://www.makelinux.net/books/lkd2/ch07lev1sec1
• http://www.makelinux.net/books/lkd2/ch07lev1sec2
• http://www.makelinux.net/ldd3/chp-10-sect-4
• http://www.makelinux.net/books/ulk3/understandlk-CHP-4-SECT-7
• http://www.makelinux.net/books/ulk3/understandlk-CHP-4-SECT-8
• http://www.makelinux.net/books/lkd2/ch07lev1sec1

Historical

• BH - Removed in 2.5
• Task queues - Removed in 2.5
• http://people.netfilter.org/rusty/unreliable-guides/kernel-hacking/basics-softirqs.html
• http://www.tldp.org/LDP/tlk/kernel/kernel.html

IPC

• ls /proc/sysvipc/
• http://www.tldp.org/LDP/tlk/ipc/ipc.html
• http://www.tldp.org/LDP/lki/lki-5.html