sunyiming
3 years ago
11 changed files with 351 additions and 18 deletions
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.idea/ |
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.idea/ |
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.DS_Store |
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From hjd(brace) |
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Intel Defined CPU Exception Table (see notes) |
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Interrupt Function |
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0 Divide by zero |
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1 Single step |
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2 Non-maskable (NMI) |
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3 Breakpoint |
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4 Overflow trap |
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5 BOUND range exceeded (186,286,386) |
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6 Invalid opcode (186,286,386) |
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7 Coprocessor not available (286,386) |
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8 Double fault exception (286,386) |
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9 Coprocessor segment overrun (286,386) |
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A Invalid task state segment (286,386) |
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B Segment not present (286,386) |
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C Stack exception (286,386) |
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D General protection exception (286,386) |
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E Page fault (286,386) |
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F Reserved |
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10 Coprocessor error (286,386) |
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IBM PC Hardware Interrupt Table (in order of priority) |
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IRQ# Interrupt Function |
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IRQ0 8 timer (55ms intervals, 18.2 per second) |
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IRQ1 9 keyboard service required |
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IRQ2 A slave 8259 or EGA/VGA vertical retrace |
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IRQ8 70 real time clock (AT,XT286,PS50+) |
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IRQ9 71 software redirected to IRQ2 (AT,XT286,PS50+) |
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IRQ10 72 reserved (AT,XT286,PS50+) |
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IRQ11 73 reserved (AT,XT286,PS50+) |
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IRQ12 74 mouse interrupt (PS50+) |
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IRQ13 75 numeric coprocessor error (AT,XT286,PS50+) |
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IRQ14 76 fixed disk controller (AT,XT286,PS50+) |
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IRQ15 77 reserved (AT,XT286,PS50+) |
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IRQ3 B COM2 or COM4 service required, (COM3-COM8 on MCA PS/2) |
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IRQ4 C COM1 or COM3 service required |
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IRQ5 D fixed disk or data request from LPT2 |
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IRQ6 E floppy disk service required |
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IRQ7 F data request from LPT1 (unreliable on IBM mono) |
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Interrupt Table as Implemented by System BIOS/DOS |
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INT # Locus Function |
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0 CPU divide by zero |
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1 CPU single step |
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2 CPU non-maskable |
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3 CPU breakpoint |
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4 CPU overflow trap |
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5 BIOS print screen |
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6 CPU Invalid opcode (186,286,386) |
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7 CPU coprocessor not available (286,386) |
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8 IRQ0 timer (55ms intervals, 18.21590 per second) |
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9 IRQ1 keyboard service required (see INT 9) |
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A IRQ2 slave 8259 or EGA/VGA vertical retrace |
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B IRQ3 COM2 service required (PS/2 MCA COM3-COM8) |
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C IRQ4 COM1 service required |
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D IRQ5 fixed disk or data request from LPT2 |
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E IRQ6 floppy disk service required |
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F IRQ7 data request from LPT1 (unreliable on IBM mono) |
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10 BIOS video (see INT 10) |
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11 BIOS Equipment determination (see INT 11) |
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12 BIOS memory size (see INT 12) |
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13 BIOS disk I/O service (see INT 13) |
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14 BIOS serial communications (see INT 14) |
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15 BIOS system services, cassette (see INT 15) |
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16 BIOS keyboard services (see INT 16) |
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17 BIOS parallel printer (see INT 17) |
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18 BIOS ROM BASIC loader |
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19 BIOS bootstrap loader (unreliable, see INT 19) |
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1A BIOS time of day (see INT 1A) |
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1B BIOS user defined ctrl-break handler (see INT 1B) |
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1C BIOS user defined clock tick handler (see INT 1C) |
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1D BIOS 6845 video parameter pointer |
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1E BIOS diskette parameter pointer (base table) |
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1F BIOS graphics character table |
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20 DOS general program termination |
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21 DOS function request services (see INT 21) |
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22 DOS terminate address (see INT 22) |
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23 DOS control break termination address (see INT 23) |
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24 DOS critical error handler (see INT 24) |
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25 DOS absolute disk read (see INT 25) |
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26 DOS absolute disk write (see INT 26) |
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27 DOS terminate and stay resident (see INT 27) |
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28 DOS idle loop, issued by DOS when idle (see INT 28) |
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29 DOS fast TTY console I/O (see INT 29) |
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2A DOS critical section and NETBIOS (see INT 2A) |
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2B DOS internal, simple IRET in DOS 2.0-5.0 |
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2C DOS internal, simple IRET in DOS 2.0-5.0 |
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2D DOS internal, simple IRET in DOS 2.0-5.0 |
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2E DOS exec command from base level command |
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interpreter (see INT 2E) |
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2F DOS multiplexer (see INT 2F) |
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30-31 CPM far jump vector for CPM (not an interrupt) |
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31 DPMI DOS Protected Mode Interface (for DOS extenders) |
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32 reserved |
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33 mouse support (see INT 33) |
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34-3E Microsoft/Borland floating point emulation |
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3F overlay manager |
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40 BIOS hard disk |
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41 BIOS fixed disk 0 parameters pointer (see INT 13,9) |
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42 BIOS relocated video handler (EGA/VGA/PS) |
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43 BIOS user font table (EGA/VGA/PS) |
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44 BIOS first 128 graphics characters (also Netware) |
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45 BIOS reserved for BIOS |
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46 BIOS fixed disk 1 parameters ptr (see INT 13,9/INT 41) |
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47 BIOS reserved for BIOS |
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48 BIOS PCjr cordless keyboard translation |
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49 BIOS PCjr non-keyboard scancode translation table |
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4A BIOS user alarm (AT,CONV,PS/2) (see INT 4A) |
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4B-4F BIOS reserved |
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50 BIOS periodic alarm from timer (PS/2) |
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51-58 BIOS reserved |
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59 BIOS GSS Computer Graphics Interface |
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5A BIOS cluster adapter BIOS entry point |
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5B BIOS cluster adapter boot |
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5C NETBIOS NETBIOS interface, TOPS interface |
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5D-5F BIOS reserved for BIOS |
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60-67 reserved for user software interrupts |
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67 EMS LIM/EMS specification (see INT 67) |
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68 APPC |
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69-6B reserved by IBM |
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6C DOS DOS 3.2 real time clock update |
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BIOS system resume vector |
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6D-6F reserved |
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70 IRQ8 real time clock (AT,XT286,PS50+, see INT 15) |
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71 IRQ9 software redirected to IRQ2 (AT,XT286,PS50+) |
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72 IRQ10 reserved (AT,XT286,PS50+) |
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73 IRQ11 reserved (AT,XT286,PS50+) |
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74 IRQ12 mouse interrupt (PS50+) |
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75 IRQ13 numeric coprocessor NMI error (AT,XT286,PS50+) |
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76 IRQ14 fixed disk controller (AT,XT286,PS50+) |
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77 IRQ15 reserved (AT,XT286,PS50+) |
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78-79 unused |
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80-85 ROM BASIC |
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86-F0 DOS reserved for BASIC interpreter use |
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86 NETBIOS NETBIOS relocated INT 18 |
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E0 CPM CP/M 86 function calls |
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F1-FF reserved by IBM |
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FE-FF may be destroyed by return from protected |
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mode using VDISK on 286 machines (Apr 86, DDJ) |
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@ -1 +1 @@ |
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这里是读者们上传的，请尽情发挥你们的见解吧！ |
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这里的世界，交给大家一起建设！ |
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23回补充内容 by sn： |
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0.11 的调度函数 schedule，在文件 kernel/sched.c 中定义为： |
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```c |
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while (1) { |
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c = -1; next = 0; i = NR_TASKS; p = &task[NR_TASKS]; |
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// 找到 counter 值最大的就绪态进程 |
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while (--i) { |
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if (!*--p) continue; |
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if ((*p)->state == TASK_RUNNING && (*p)->counter > c) |
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c = (*p)->counter, next = i; |
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} |
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// 如果有 counter 值大于 0 的就绪态进程，则退出 |
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if (c) break; |
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// 如果没有： |
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// 所有进程的 counter 值除以 2 衰减后再和 priority 值相加， |
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// 产生新的时间片 |
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for(p = &LAST_TASK ; p > &FIRST_TASK ; --p) |
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if (*p) (*p)->counter = ((*p)->counter >> 1) + (*p)->priority; |
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} |
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// 切换到 next 进程 |
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switch_to(next); |
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``` |
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由上面的程序可以看出，0.11 的调度算法是选取 `counter` 值最大的就绪进程进行调度。 |
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当没有 counter 值大于 0 的就绪进程时，要对所有的进程做 `(*p)->counter = ((*p)->counter >> 1) + (*p)->priority`。 |
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其效果是对所有的进程（**包括阻塞态进程**）都进行 counter 的衰减，并再累加 priority 值。这样，对正被阻塞的进程来说，其此时的counter不为0，那么计算后得到的counter大于就绪态进程。 |
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于是可知，**一个进程在阻塞队列中停留的时间越长，其优先级越大，被分配的时间片也就会越大**。 |
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所以总的来说，Linux 0.11 的进程调度是一种**综合考虑进程优先级并能动态反馈调整时间片的轮转调度算法**。 |
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## 进程 counter 是如何初始化的 |
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首先回答第一个问题，显然这个值是在 fork() 中设定的。Linux 0.11 的 `fork()` 会调用 `copy_process()` 来完成从父进程信息拷贝（所以才称其为 fork），看看 `copy_process()` 的实现，会发现其中有下面两条语句： |
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```c |
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// 用来复制父进程的PCB数据信息，包括 priority 和 counter |
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*p = *current; |
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// 初始化 counter |
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p->counter = p->priority; |
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// 因为父进程的counter数值已发生变化，而 priority 不会，所以上面的第二句代码将p->counter 设置成 p->priority。 |
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// 每个进程的 priority 都是继承自父亲进程的，除非它自己改变优先级。 |
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``` |
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①假设没有改变优先级，时间片的初值就是进程 0 的 priority，即宏 INIT_TASK 中定义的： |
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```c |
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#define INIT_TASK \ |
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{ 0,15,15, |
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// 上述三个值分别对应 state、counter 和 priority; |
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``` |
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## 当进程的时间片用完时，被重新赋成何值？ |
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接下来回答第二个问题，当就绪进程的 counter 为 0 时，不会被调度（schedule 要选取 counter 最大的，大于 0 的进程），而当所有的就绪态进程的 counter 都变成 0 时，会执行下面的语句： |
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```c |
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(*p)->counter = ((*p)->counter >> 1) + (*p)->priority; |
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``` |
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算出的新的 counter 值也等于 priority，即初始时间片的大小。 |
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