F9 Microkernel code reading part 2 scheduling
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F9 is an experimental microkernel used to construct flexible embedded systems. It implements a tickless scheduler to improve energy efficiency by avoiding periodic timer interrupts. The scheduler code uses scheduling slots and a thread control block to select the next runnable thread. Important files related to scheduling include sched.c, ktimer.c, and thread.c. The kernel aims to support real-time and time-sharing applications on ARM Cortex-M microprocessors.
![Scheduling
related
code
•
•
•
•
•
•
•
ipc.c
kMmer.c
sched.c
(most
important)
so]irq.c
syscall.c
systhread.c
thread.c](https://image.slidesharecdn.com/f9-microkernelcodereadingpart2scheduling-131120201355-phpapp01/85/F9-Microkernel-code-reading-part-2-scheduling-10-320.jpg)
F9 Microkernel code reading part 2 scheduling
- 1. Part 2 : Code Reading of F9 Microkernel Scheduling ben6 2013-‐11-‐18
- 2. F9 Agenda • Brief of F9 Microkernel Scheduling • All about Algorithms • Scheduling Code reading
- 3. F9 Agenda • Brief of F9 Microkernel Scheduling • All about Algorithms • Scheduling Code reading
- 4. F9 Microkernel Overview • an experimental microkernel used to construct flexible embedded systems inspired by famous L4 microkernel. • The moMvaMon of F9 microkernel is to deploy modern kernel techniques to support – running real-‐Mme and Mme-‐sharing applicaMons (ex: wireless communicaMons) for ARM Cortex-‐M series microprocessors with efficiency (performance + power consumpMon) – security (memory protecMon + isolated execuMon)
- 5. CharacterisMcs • Energy efficient scheduling • Tickless Mmer
- 6. Mckless scheduler • F9 implements a Mckless scheduler which implies the dynamic Mmer. • You can track the development here: hWps://github.com/southernbear/RIOT/wiki/ Development • F9 follows some concepts about TiROS for Mckless: hWp://Mros.sourceforge.net/
- 7. F9 Agenda • Brief of F9 Microkernel Scheduling • All about Algorithms • Scheduling Code reading
- 8. Tickless Scheduling • Reference concept of TiROS • TiROS avoids most context-‐switching overhead costs by eliminaMng periodic Mcks. • Most embedded real-‐Mme OSes, a trade off between high Mme-‐resoluMon (by increasing Mck frequency) and overhead. • TiROS does not use Mcks and achieves high-‐ Mme resoluMon with very low overhead.
- 9. F9 Agenda • Brief of F9 Microkernel Scheduling • All about Algorithms • Scheduling Code reading
- 10. Scheduling related code • • • • • • • ipc.c kMmer.c sched.c (most important) so]irq.c syscall.c systhread.c thread.c
- 11. KMmer_handler Timer handler in ISR vector table
- 12. kMmer_handler Hardware interrupt trigger ktmer_handler
- 13. Plaborm/irq.h: schedule_in_irq Trigger point of scheduling which while IRQ event occurs include/plaborm/irq.h
- 16. Scheduler slots • sched.h sched.h 26 typedef struct sched_slot { 27 tcb_t *ss_scheduled; 28 sched_handler_t ss_handler; 29 } sched_slot_t; sched_slot_t ss_scheduled ss_handler Priority in order
- 17. Schedule handler typedef tcb_t *(*sched_handler_t)(struct sched_slot *slot);
- 18. Select target thread ss_handler is used while currnt slot thread is empty or not runnable
- 19. thread_state_t Only scheduling for T_RUNNABLE State
- 20. Thread control block TCB using by schedule slots
- 21. __NAKED • __aWribute__((naked)) Using While IRQ funcMon Use this aWribute on the ARM, AVR, MCORE, MSP430, NDS32, RL78, RX and SPU ports to indicate that the specified funcMon does not need prologue/epilogue sequences generated by the compiler. It is up to the programmer to provide these sequences. The only statements that can be safely included in naked funcMons are asm statements that do not have operands. All other statements, including declaraMons of local variables, if statements, and so forth, should be avoided. Naked funcMons should be used to implement the body of an assembly funcMon, while allowing the compiler to construct the requisite funcMon declaraMon for the assembler.
- 24. thread.c
- 25. Conclusion • F9 Microkernel uses following concepts – Tickless Scheduling – Dynamic Timer To archive energy efficiency scheduling
- 26. Discussions F9 ?
- 27. Kernel line of code for reading Kernel C code line: 2183 Git head: 4d87f204252d57525f9cd93f163ca5225cc34bb7
- 28. References • F9 Microkernel source code and introducMon • hWps://github.com/southernbear/RIOT/wiki/Development • TiROS for Mckless hWp://Mros.sourceforge.net/ • GCC Naked AWribute