慶應義塾大学
2012年度 春学期

システム・ソフトウェア
System Software / Operating Systems

2012年度春学期 火曜日2時限
科目コード: 60730
開講場所:SFC
授業形態:講義
担当: Rodney Van Meter
E-mail: rdv@sfc.keio.ac.jp

第13回 7月13日 リアルタイムOS
Lecture 13, July 13: Real-Time Operating Systems

Outline

Links of the Day

David Malan's introductory computer science class at Harvard
Launch of the space shuttle Columbia, April 12, 1981 (I was there.)

Today's Picture

Fast food!
  (nagashi-soumen)

Real-Time Operating Systems

Scheduling

Basic Priority Scheduling

A few weeks ago we saw basic priority scheduling, in the example of VxWorks on Mars. VxWorks is a good example of an embedded OS, and also includes real-time operation.

Goals of General-Purpose Scheduling

Do those goals still hold in real-time OSes? No!

Real-time: Deadline Scheduling

Airplanes falling from the sky, death and destruction all around. We don't want that, do we? Then don't play Tetris on your flight avionics hardware...

  • CPU scheduling is perhaps the most important aspect, but the principles apply to other resources, as well.
  • Several mechanisms can be used:
    • Shortest job first
    • Deadline: Job with the earliest deadline is chosen
    • Slack: Job with the least "slack" (room for error/time to waste) is chosen
    • FIFO: Just what it sounds like, and only good in certain circumstances

Jensen, Locke and Tokuda talk about the value of completing a particular task at a particular time:

Some possible
      cases of value functions for computation, from Jensen

Once the value reaches zero, there is no point in executing the task. Question: What might some tasks be that would have each of those classes of value function?

Here is an example of what a schedule might look like if we had one of each kind of task, all started at the same time:

An example of
  four scheduling cases of value functions for computation, from Jensen

Homework

None, just work on your project.

Next Lecture

Next lecture:

第14回 7月19日 Operating Systemsの研究
Lecture 14, July 19: Operating Systems Research

Readings for next week and followup for this week:

Follow-up: You should look up both the real-time and embedded capabilities of

その他 Additional Information