02 04 Operating System Services P4 — Transcript

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1. 0:08[Music]
2. 0:20next
3. 0:21operating system structure
4. 0:24so for efficient performance and
5. 0:26implementation of os should be
6. 0:28partitioned into a separate subsystems
7. 0:32so each with carefully defined tasks
8. 0:36inputs and outputs
9. 0:38and performance characteristics
10. 0:40these subsystems can be arranged in
11. 0:43various architectural configurations so
12. 0:45it could be a simple structure like that
13. 0:47of ms-dos a more complex like that of
14. 0:50unix
15. 0:51layered or an abstraction
16. 0:54and micro kernel
17. 0:56alright
18. 0:57so let's take this let's start with
19. 1:00the monolithic structure okay
20. 1:03this is original in unix
21. 1:05okay so what do we mean by monolithic
22. 1:08okay so a monolithic kernel is an
23. 1:10operating system architecture
24. 1:13where the entire operating system is
25. 1:14working in kernel space
26. 1:17okay so the monolithic model differs
27. 1:20from other operating systems
28. 1:22architecture
29. 1:23such as the microkernel architecture in
30. 1:25that it alone defines
31. 1:27a high-level virtual interface over
32. 1:30computer hardware
33. 1:32okay
34. 1:34next
35. 1:39so traditional unix system structure
36. 1:42okay so you've got the kernel here
37. 1:44all right so the users
38. 1:47interacting with the shells all right
39. 1:49and the shells okay so you've got a
40. 1:52system called interface the kernel
41. 1:54and then these are the services
42. 1:56okay so that's how traditional unix
43. 1:58system architecture works
44. 2:00so beyond simple but fully layered
45. 2:03okay
46. 2:05next for the linux system structure
47. 2:07monolithic plus modular design
48. 2:10okay
49. 2:11so
50. 2:13basically linux has innovated
51. 2:16the
52. 2:17unix systems all right
53. 2:20using this um the traditional monolithic
54. 2:23and unix
55. 2:24plus the modular design
56. 2:26okay
57. 2:28you also have the layered approach
58. 2:30okay so another approach is to break the
59. 2:33os into a number of smaller layers
60. 2:37each of which rests on the layer below
61. 2:40it
62. 2:41okay
63. 2:42and relies solely on the surfaces
64. 2:44provided by the next lower layers so
65. 2:46this approach allows each layer
66. 2:49to be developed and debugged
67. 2:51independently
68. 2:53so with the assumption that all lower
69. 2:54layers have already been debugged
70. 2:57and are trusted to deliver system
71. 2:59properties
72. 3:07all right
73. 3:08so the problem is deciding what order
74. 3:11in which to place the layers
75. 3:14as no layer can upon
76. 3:17the services of a higher layer so
77. 3:20many chicken and egg situations may
78. 3:23arise
79. 3:24right
80. 3:25so layered approach can also be less
81. 3:27efficient as the request from service
82. 3:30from a higher layer has to filter
83. 3:32through a lower layers before it reaches
84. 3:34the hardware
85. 3:35okay so like what we see here
86. 3:37so to reach the hardware you have to go
87. 3:40through several layers and possibly with
88. 3:43significant processing at each step all
89. 3:46right
90. 3:48okay so next is microkernel
91. 3:54so the basic idea behind microkernel is
92. 3:56to remove all the non-essential services
93. 3:59from the kernel
94. 4:00and implement them as system
95. 4:02applications instead
96. 4:04so thereby
97. 4:05making the kernel as small and efficient
98. 4:07as possible
99. 4:09okay
100. 4:10so most microkernels provide basic
101. 4:12process and memory management and
102. 4:14message passing between other services
103. 4:17and not much more
104. 4:19okay
105. 4:21so
106. 4:22most
107. 4:23our security and protection can be
108. 4:25enhanced as most services
109. 4:28are performed in the user mode not in
110. 4:30the kernel mode anymore
111. 4:32so system expansion
112. 4:34can also be easier
113. 4:36because it only involves adding more
114. 4:39system applications and not rebuilding a
115. 4:42new kernel
116. 4:43okay
117. 4:44so that that's the benefits of it okay
118. 4:48so mac
119. 4:50was the first and most widely known
120. 4:52microkernel and now forms a major
121. 4:54component for the map osx
122. 4:57okay so the first to adopt this okay
123. 5:00it was mac okay mac is an example of
124. 5:03microkernel
125. 5:05and it has
126. 5:07the influence of the modern mac os x
127. 5:12okay so they call it darwin
128. 5:15okay so in windows nt
129. 5:17okay this is from microsoft i mean the
130. 5:19microsoft windows nt was originally
131. 5:21microkernel but suffered from
132. 5:23performance problem relative to windows
133. 5:2595
134. 5:27nt powerpoint 0 improved performance
135. 5:30by moving more services into the kernel
136. 5:34and
137. 5:35now xp is back being more monolithic
138. 5:39i like windows xp you know so for me
139. 5:40it's the most
140. 5:42stable operating system from microsoft
141. 5:45okay
142. 5:46another micro kernel example is qnx
143. 5:49a real time os for embedded systems
144. 5:57okay so this is how a micro calendar
145. 6:00system architecture look like you've got
146. 6:02the user mode there kernel some of the
147. 6:04functionalities are not anymore in the
148. 6:06kernel mode
149. 6:07okay and instead they have converted it
150. 6:10into
151. 6:11an application program instead
152. 6:13okay so it's much faster
153. 6:16next is modules
154. 6:18okay so modern os development is well
155. 6:22nowadays most of the software
156. 6:24developments or even the os developments
157. 6:26are using the object oriented okay
158. 6:28with a relatively small core kernel and
159. 6:31set of modules which can be linked in
160. 6:33dynamically
161. 6:36all right so see for example the solaris
162. 6:39structure okay so which we will show
163. 6:41later on okay so modules are similar to
164. 6:44the layers
165. 6:46in that each subsystem has clearly
166. 6:48defined tasks and interfaces but any
167. 6:51module is free to contact any other
168. 6:53modules eliminating the problems of
169. 6:56going through multiple intermediary
170. 6:57layers
171. 6:58as well as chicken and egg problems all
172. 7:02right
173. 7:03so the kernel is relatively small in
174. 7:05this architecture
175. 7:08similar to microkernels but
176. 7:10the kernel does not have to implement
177. 7:12message passing since modules are free
178. 7:15to contact
179. 7:16each other directly so that's the
180. 7:18advantage or the good side of it
181. 7:20okay
182. 7:22next
183. 7:23hybrid systems
184. 7:25so most oss today do not strictly adhere
185. 7:27to one architecture okay so that's why
186. 7:30it's called hybrid systems it's a
187. 7:31combination of different
188. 7:33uh systems presented so but hybrids are
189. 7:36of several okay so like the mac os or
190. 7:40the apple mac os x hybrid
191. 7:42layered aqua ui plus kakoa programming
192. 7:45environment
193. 7:47all right
194. 7:51so the mac os and the ios structures is
195. 7:53basically on this um
196. 7:57uh stocks you've got the applications
197. 8:00you can communicate okay or user
198. 8:02experience
199. 8:03directly accessing the application
200. 8:06frameworks core frameworks and the
201. 8:08kernel environment called darwin
202. 8:10okay darwin is on mac os
203. 8:14and ios and this is how it looked like
204. 8:16the organization of darwin
205. 8:18is on this diagram or figure here
206. 8:22all right
207. 8:25next how about for android
208. 8:27for android the android os was developed
209. 8:30for android smartphones and tablets by
210. 8:32an open handset alliance so primarily
211. 8:36it's google all right
212. 8:38so it's an open source
213. 8:41similar stack to ios
214. 8:44okay
215. 8:46so android is an open source os as
216. 8:48opposed to ios of course which is
217. 8:50proprietary
218. 8:51which has led to its popularity okay so
219. 8:55android includes versions of linux and a
220. 8:58java virtual machine
221. 8:59both optimized for small platforms
222. 9:03okay so android apps are developed using
223. 9:07a special java for android development
224. 9:09environment
225. 9:12so this is a
226. 9:14android architecture
227. 9:16okay so similar to that of the ios
228. 9:19architecture
229. 9:20okay
230. 9:22next
231. 9:24building and booting and operating
232. 9:26systems
233. 9:29so operating systems generally designed
234. 9:31to run on a class of systems
235. 9:33with variety of peripherals so commonly
236. 9:37operating system already installed on
237. 9:39purchased computers right
238. 9:42so we have this oem type of operating
239. 9:44systems right when you purchase
240. 9:46an operating system so when you purchase
241. 9:49a laptop so an operating system is
242. 9:50already built in it
243. 9:52okay
244. 9:53so but can build and install some other
245. 9:56operating system so if generating an
246. 9:58operating system from scratch
247. 10:00so write the operating system source
248. 10:02code okay
249. 10:03this one is a challenge
250. 10:05okay so configure the operating system
251. 10:07for the system on which it will run
252. 10:10compile the operating system
253. 10:12install the operating system and boot
254. 10:14the computer and its new operating
255. 10:16system
256. 10:19all right
257. 10:20so building and booting linux so you can
258. 10:23do this okay give it a try so download
259. 10:25the linux source code okay so at
260. 10:27kernel.org
261. 10:29configure the kernel via the mini config
262. 10:32okay compile the kernel using make
263. 10:35okay
264. 10:36so you can have build and
265. 10:40boot linux systems
266. 10:42okay
267. 10:45next is system boot
268. 10:48so when power initialized on the system
269. 10:51execution starts at a fixed memory
270. 10:53location
271. 10:54okay so the operating system must be
272. 10:56made available to hardware so hardware
273. 10:58can start it so a small piece of code
274. 11:00bootstrap loader bios is stored in a rom
275. 11:03or eprom locates the kernel load
276. 11:05into a memory and starts it okay so this
277. 11:08is what usually happens during the power
278. 11:10and self test now all right so in your
279. 11:12system is about to boot
280. 11:14okay
281. 11:15now common bootstrap loader
282. 11:18the grub or the groove
283. 11:20allow selection of kernel from multiple
284. 11:23disks versions and kernel options
285. 11:26so kernel loads the system
286. 11:29and system is then running
287. 11:31okay so boot loaders frequently allow
288. 11:34various boot states such as a single
289. 11:36user mode now in cisco
290. 11:39these cisco devices even has an ios
291. 11:42all right or the internet operating
292. 11:43systems
293. 11:45okay and the booting process is similar
294. 11:48to that of
295. 11:49a computer
296. 11:52if you will still remember now in cisco
297. 11:56we considered
298. 11:57a router as a computer why
299. 12:00because every component of a computer is
300. 12:03available in the router
301. 12:04so the way windows are the way
302. 12:07computers boot up is also the same way
303. 12:10as the router and switches boot up
304. 12:13all right
305. 12:17next operating system debugging
306. 12:19debugging is finding and fixing errors
307. 12:22just like in programming okay
308. 12:24also performance tuning os generate log
309. 12:27files containing in error information
310. 12:30so failure of an application can
311. 12:32generate core dump
312. 12:34okay file capturing memory of the
313. 12:36process or the operating system failure
314. 12:38can generate crash dump
315. 12:40containing the kernel memory
316. 12:43right so beyond crashes performance
317. 12:46tuning can optimize system performance
318. 12:48okay
319. 12:51next performance tuning
320. 12:53just like in task manager so we can
321. 12:55improve the performance by removing
322. 12:57battle necks
323. 12:58okay so os must provide means of
324. 13:01computing and displaying measures of the
325. 13:03system behavior by in windows we are
326. 13:05using the task manager to see the
327. 13:08behavior of our computer
328. 13:10okay and we can
329. 13:12remove or we can end tasks some of the
330. 13:15applications that we see cause
331. 13:17bottlenecks over the performance okay or
332. 13:20that would cost per more performance
333. 13:22aggregation on our computer systems
334. 13:25okay
335. 13:27next is tracing tracing collects data
336. 13:31for specific events such as steps
337. 13:33involved in a system called invocation
338. 13:36okay tools includes like stress i have
339. 13:39mentioned stress earlier right
340. 13:41so trace system calls invoke bear
341. 13:43process
342. 13:44or the gdb source level debugger perf
343. 13:48collection of linux performance tools or
344. 13:51the tcp dump
345. 13:53collects network packets
346. 13:55okay so we use tcp dump in windows or in
347. 13:58in
348. 13:59networks all right that's a very useful
349. 14:02command there
350. 14:04okay
351. 14:05so this would be the last slide
352. 14:08the bcc okay or the bpf compiler
353. 14:11collection
354. 14:13so debugging interactions between user
355. 14:15level and kernel code nearly impossible
356. 14:17without tool set that understands both
357. 14:20and an instrument
358. 14:22their actions okay so this bcc is a rich
359. 14:25toolkit providing tracing features for
360. 14:28linux
361. 14:29alright
362. 14:30so this one is for linux
363. 14:42[Music]
364. 14:50you