操作系统实验磁盘调度

1、操作系统实验报告课程名称操作系统实验课程编号0920311实验项目名称磁盘调度算法学号年级专业学生所在学院软件学院指导教师王宏斌实验室名称地点计算机软件第二实验室 21#282文档第十讲 磁盘调度算法一、实验概述1. 实验名称磁盘调度算法2. 实验目的通过学习 EOS 实现磁盘调度算法的机制， 掌握磁盘调度算法执行的条件和时机； 察EOS实现的FCFS、SSTF和SCAN磁盘调度算法，了解常用的磁盘调度算法；编写 CSCAN和N-Step-SCAN磁盘调度算法，加深对各种扫描算法的理解。3. 实验类型验证设计4. 实验容理解EOS是如何实现磁盘调度算法的；学习EOS是如何测试磁盘调度算法的，并

2、体会这种测试方法的优缺点。二、实验环境操作系统： Windows XP 操作系统集成实验环境软件： Tevation OS Lab编译语言： C 参考书： EOS 操作系统实验教程三、实验过程1实验指导P176-3.2验证先来先服务（FCFS ）磁盘调度算法，要求请给出在“输出” 窗口中的结果。* Disk schedule start working *Start Cylinder: 10TID: 31 Cylinder: 8 Offset: 2 -TID: 32 Cylinder: 21 Offset: 13 +TID: 33 Cylinder: 9 Offset: 12 -TID: 34

3、 Cylinder: 78 Offset: 69 +TID: 35 Cylinder: 0 Offset: 78 -TID: 36 Cylinder: 41 Offset: 41 +TID: 37 Cylinder: 10 Offset: 31 -TID: 38 Cylinder: 67 Offset: 57 +TID: 39 Cylinder: 12 Offset: 55 -TID: 40 Cylinder: 10 Offset: 2 -Total offset: 360 Transfer times: 10 Average offset: 362实验指导P177-3.3验证验证最短寻道时间

4、优先（ SSTF）磁盘调度算法，要求请给出在“输出”窗口中的结果。* Disk schedule start worki ng *Start Cyli nder: 10TID: 37 Cyli nder: 10 Offset: 0 =TID: 40 Cyli nder: 10 Offset: 0 =TID: 33 Cylinder: 9 Offset: 1 -TID: 31 Cylinder: 8 Offset: 1 -TID: 39 Cyli nder: 12 Offset: 4 +TID: 32 Cylinder: 21 Offset: 9 +TID: 36 Cylinder: 41 Of

5、fset: 20 +TID: 38 Cylinder: 67 Offset: 26 +TID: 34 Cylinder: 78 Offset: 11 +TID: 35 Cylinder: 0 Offset: 78 -Total offset: 150 Tran sfer times: 10 Average offset: 153实验指导P178-3.4验证SSTF算法造成的线程“饥饿”现象，要求请给出在“输出 窗口中的结果。* Disk schedule start worki ng *Start Cyli nder: 10TID: 37 Cyli nder: 10 Offset: 0 =TI

6、D: 40 Cyli nder: 10 Offset: 0 =TID: 33 Cylinder: 9 Offset: 1 -TID: 34 Cylinder: 8 Offset: 1 -TID: 35 Cylinder: 11 Offset: 3 +TID: 39 Cylinder: 12 Offset: 1 +TID: 32 Cylinder: 21 Offset: 9 +TID: 36 Cylinder: 41 Offset: 20 +TID: 38 Cylinder: 67 Offset: 26 +TID: 31 Cylinder: 78 Offset: 11 +Total offset

7、: 72 Transfer times: 10 Average offset: 74.实验指导 P179-3.5 验证扫描 （SCAN ）磁盘调度算法， 要求在非饥饿 （即实验指导P176-3.2 节中的数据）和饥饿（即实验指导 P178-3.4 节中的数据）请给出在“输出”窗 口中的结果，并且要求在每次输入两次“ds”命令（注意不要连续输入，要等第一次“ds”命令执行完，再输入第二次"ds”命令），分析结果为什么不同。非饥饿下第一次：* Disk schedule start working *Start Cylinder: 10TID: 37 Cylinder: 10 Offse

8、t: 0 =TID: 40 Cylinder: 10 Offset: 0 =TID: 39 Cylinder: 12 Offset: 2 +TID: 32 Cylinder: 21 Offset: 9 +TID: 36 Cylinder: 41 Offset: 20 +TID: 38 Cylinder: 67 Offset: 26 +TID: 34 Cylinder: 78 Offset: 11 +TID: 33 Cylinder: 9 Offset: 69 -TID: 31 Cylinder: 8 Offset: 1 -TID: 35 Cylinder: 0 Offset: 8 -Total

9、 offset: 146 Transfer times: 10 Average offset: 14非饥饿下第二次：* Disk schedule start working *Start Cylinder: 10TID: 47 Cylinder: 10 Offset: 0 =TID: 50 Cylinder: 10 Offset: 0 =TID: 43 Cylinder: 9 Offset: 1 -TID: 41 Cylinder: 8 Offset: 1 -TID: 45 Cylinder: 0 Offset: 8 -TID: 49 Cylinder: 12 Offset: 12 +TID

10、: 42 Cylinder: 21 Offset: 9 +TID: 46 Cylinder: 41 Offset: 20 +TID: 48 Cylinder: 67 Offset: 26 +TID: 44 Cylinder: 78 Offset: 11 +Total offset: 88 Transfer times: 10 Average offset: 8 饥饿第一次：* Disk schedule start working *Start Cylinder: 10TID: 37 Cylinder: 10 Offset: 0 =TID: 40 Cylinder: 10 Offset: 0

11、=TID: 35 Cylinder: 11 Offset: 1 +TID: 39 Cylinder: 12 Offset: 1 +TID: 32 Cylinder: 21 Offset: 9 +TID: 36 Cylinder: 41 Offset: 20 +TID: 38 Cylinder: 67 Offset: 26 +TID: 31 Cylinder: 78 Offset: 11 +TID: 33 Cylinder: 9 Offset: 69 -TID: 34 Cylinder: 8 Offset: 1 -Total offset: Transfer times: 10 Average

12、offset: 13 饥饿第二次：* Disk schedule start working *Start Cylinder: 10TID: 47 Cylinder: 10 Offset: 0 =TID: 50 Cylinder: 10 Offset: 0 =TID: 43 Cylinder: 9 Offset: 1 -TID: 44 Cylinder: 8 Offset: 1 -TID: 45 Cylinder: 11 Offset: 3 +TID: 49 Cylinder: 12 Offset: 1 +TID: 42 Cylinder: 21 Offset: 9 +TID: 46 Cyli

13、nder: 41 Offset: 20 +TID: 48 Cylinder: 67 Offset: 26 +TID: 41 Cylinder: 78 Offset: 11 +Total offset: 72 Transfer times: 10 Average offset: 7分析： 两次 ds 的寻道方向不一样。 由于定义了一个布尔类型的全局变量 ScanInside ，用 于表示扫描算法中磁头移动的方向。该变量值为 TRUE 时表示磁头向移动(磁道号增加)； 值为 FALSE 时表示磁头向外移动(磁道号减少)。该变量初始化为 TRUE ，表示 SCAN 算 法第一次执行时，磁头向移动。然

14、后TRUE变成FLASE，所以实验中两次 ds的结果就发生了变化。5 改写 SCAN 算法算法：PREQUESTIopDiskSchedule(VOID)PLIST_ENTRY pListEntry;PREQUEST pRequest;LONG Offset;ULONG InsideShortestDistance = 0xFFFFFFFF;ULONG OutsideShortestDistance = 0xFFFFFFFF;PREQUEST pNextRequest = NULL;PREQUEST pNextRequestn = NULL; PREQUEST pNextRequestw =

15、NULL;for (pListEntry = RequestListHead.Next; pListEntry != &RequestListHead; pListEntry = pListEntry->Next) pRequest = CONTAINING_RECORD(pListEntry, REQUEST, ListEntry); Offset = pRequest->Cylinder - CurrentCylinder;if (0 = Offset) pNextRequest = pRequest;goto RETURN; else if (Offset >

16、0) if (Offset < InsideShortestDistance) InsideShortestDistance = Offset; pNextRequestn = pRequest; else if (Offset < 0) if (-Offset < OutsideShortestDistance) OutsideShortestDistance = -Offset; pNextRequestw = pRequest;if(ScanInside)if(pNextRequestn!=NULL) pNextRequest=pNextRequestn;elsepNe

17、xtRequest=pNextRequestw; ScanInside=!ScanInside;elseif(pNextRequestw!=NULL) pNextRequest=pNextRequestw;elsepNextRequest=pNextRequestn; ScanInside=!ScanInside;RETURN:return pNextRequest;运行结果：* Disk schedule start working *Start Cylinder: 10TID: 37 Cylinder: 10 Offset: 0 =TID: 40 Cylinder: 10 Offset: 0 =TID: 39 Cylinder: 12 Offset: 2 +TID: 32 Cylinder: 21 Offset: 9 +TID: 36 Cylind