Software Design Process Models

Design as search. Design spaces. Design state, goal structure, generative design operations, early quantitative evaluations, control of design process. Basic models of design (transformational, plan/architecture driven). Relationship to other life-cycle activities.

Terms

• Module: a collection of classes
• Subsystem: a collection of classes with an interface
• Design window: the time, which design decision have to be made
• Service: the operation in common purpose, offered by a subsystem

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Master Theorem

T(n) = a * T(n / b) + f(n)
x    = log_b(a)
T(n) = θ(n^x)          if f(n) = O(n^(x-ε))
       θ(n^x * lg(n))  if f(n) = θ(n^x)
       θ(f(n))         if f(n) = Ω(n^(x+ε)) 
                          and a * f(n/b) <= c * f(n)

Greedy

• At each step, make the "best" next choice.
• Never backtrack or change past choices.
• Never look ahead to see if this choice has negative consequences.

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这次Assignment除了Physical Memory Management, 其他几个部分都相互关联. 所以在设计完成前几部分的时候, 最好将所有需要解决的问题都搞明白, 然后统一设计Address Space的结构.

TLB Management

和TLB有关的, 需要解决的问题有这么几个:

1. Context Switch的时候, 如果不是两个不同的thread, 则不需要flush TLB
2. 当TLB被占满的时候, 要替换最老的TLB entry
3. TLB内保存read-only信息

然后一个一个说…

1. 只要检查上一次flush TLB时候的thread, 和现在的是不是同一个thread即可
2. 这部分这次Assignment已经把code写好大半了…`你需要做的就是把tlb_get_rr_victim return回来的那个entry替换掉
3. 理解MIPS TLB的每个flag bits的用处, 然后把read-only flag放在对应的位置.
   当程序试图写入一个read-only的memory时候, vm_fault拿到的faulttype是VM_FAULT_READONLY.
   Don't PANIC!!!

TLB基本就这么多= =||`没啥东西…

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这篇文章的目的是记录CS350 Assignment2中, 我编写各种System Calls时所采用的思路. 实际coding的时候, 同一种System Call的实现方式很可能不止一种, 但殊途同归.
注1: 文章顺序和实际coding顺序并不一定一致, 请参考Assignment中的Strategy部分.
注2: 如果没有仔细读过code和Assignment...这里很有些东西你可能读的似懂非懂.

欢迎在评论中提问...

General Tips

1. 别管写什么function, 第一步永远是检查parameter是否有效!!!
   (比如, pointer是不是NULL, string是不是空, etc)
2. 不要放过任何一个warning...需要explicit cast的时候, 千万不要偷懒.
3. function一般使用parameter中的pointer进行value return, 正常的return用来return errno.
4. 开始coding之前, 除了读Assignment, 读code, 还要好好读Assignment Hint! 解答了很多FAQ
5. 注意在header file里用#ifndef, 保证header不会出现重复include
6. kmalloc了的东西...在destroy的时候一定要kfree. 不然A3里, 你会发现各种memory leak
   (Create某些data structure的中间, 如果出现error, 则需要首先free已经allocated的内存, 然后返回error)
7. 善用spl解决mutex问题. 当然, 首先你要明白什么样的操作需要mutex!

我会边写这个Note边添加Tips...

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Definition实在不知道怎么概括= =...

• Intention of a relation: relation definition and constrains
• Extention of a relation: the actual data, tuples

Relation properties

• Set Theory
  
  
  • Attributes has order (not necessary)
  • Value are used to identify tuples
  • Tuples dont have order
  • Tuples cant have duplication
• Attribute value are atomic
• Degree: How many attributes in the schema
• Cardinality: How many tuples in an instance

Constraints

• Let the DBMS to ensure the entry or modification on data are legal
• Give applications' bug no chance to ruin the data

Three Constraint Level

• Tuple-level
  
  
  • Domain restrictions (datatype)
  • Attribute comparisons (好像是指check)
• Relation-level
  
  
  • Special type of keys
    
    
    • Superkey: 能uniquely identifies a tuple的一个or一组attribute
    • Candidate key: Superkey的最小集, (最简单的一个or一组attribute)
    • Primary key: 被选中, 用来identity tuples的Candidate key
• Database-level
  
  
  • Referential integrity
    
    
    • Foreign key: 其他relation中的primary key
    • Referential integrity: 不允许出现和对应relation中的记录不符的情况
  • Inclusion dependencies: = =`不懂