Nachos Project 3. Speaker: Sheng-Wei Cheng 2010/12/16

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1 Nachos Project Speaker: Sheng-We Cheng //6

2 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson

3 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson

4 Motvaton Motvaton Nachos keeps only one user program n memory at a tme./nachos -x user_program Objectves Use the pagng mechansm to mplement the multprogrammng,.e., keep multple user programs n man memory. Pages are only loaded when they are demanded durng program executon,.e., pure demand pagng. 4

5 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson 5

6 Execute a User Program n Nachos Create a page table to run ths program Load program nto physcal memory Execute the program Object AddrSpace maps vrtual page to physcal page n one to one (:) AddrSpace::AddrSpace( ) { pagetable = new TranslatonEntry[NumPhysPages]; } AddrSpace::Load( ) AddrSpace::Execute( ). Intal regsters. Load page table regsters. Jump to the user program Kernel->machne->Run( ) for( ; ; ){ OneInstructon(nstr); //execute one nstructon kernel->nterrupt->onetck( ); //Advance tmer tck } 6

7 Map Address Space n Nachos User program Vrtual page Physcal page Vald/Invald /8 = V V V V 4 4 V 5 5 V 4 5 Physcal memory %8 = 4 Offset = V 7 Physcal page sze = 8 Number of physcal pages = 8 7

8 Load User Program Read the header of the user program The header format s NoffHeader defned n noff.h Magc number Magc number The header of code segment Vrtual address User Program Header The header of ntalzed data segment The header of read only segment Offset n fle Segment sze Code and data segments The header of unntalzed data segment Code segment 8

9 Load User Program (cont.) Load code and data segments nto man memory In Nachos, the segments are loaded nto memory wth no offset. Physcal memory Code segment Code segment Intalzed data segment Read only data segment Intalzed data segment Read only data segment 9

10 Execute One Instructon Machne::OneInstructon( ) Use ReadMem( ) to read one nstructon It wll call Machne::Translate( ) to get the physcal address by checkng the page table (AddrSpace table). Read data from the address returned from Machne::Translate( ) Parse the fetched nstructon Update PCReg and NextPCReg accordng to the executon of the fetched nstructon

11 Load Process wthout Page faults 4 5 Physcal page Vrtual page Page table 6 7 Physcal page Vrtual page User program Man memory 7 Page table User program

12 Load Process wth Page faults 4 5 Physcal page Page fault Page table Vrtual page Pure demand pagng 6 7 Physcal page Vrtual page User program 7 Man memory Page table User program

13 Load Process wth Page faults 4 5 Physcal page Vrtual page v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program 7 Man memory Page table User program

14 Load Process wth Page faults 4 5 Physcal page Page fault v Page table Vrtual page Pure demand pagng 6 7 Physcal page Vrtual page User program 7 4 Man memory Page table User program

15 Load Process wth Page faults 4 5 Physcal page Vrtual page v v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program 7 5 Man memory Page table User program

16 Load Process wth Page faults 4 5 Physcal page Vrtual page v v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program Page fault 7 6 Man memory Page table User program

17 Load Process wth Page faults 4 5 Physcal page Vrtual page v v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program v 7 7 Man memory Page table User program

18 Load Process wth Page faults 4 5 Physcal page Vrtual page v v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program v 7 8 Man memory Page fault Page table User program

19 Load Process wth Page faults 4 5 Physcal page Vrtual page v v Page table Pure demand pagng 6 7 Physcal page Vrtual page User program v v 7 9 Man memory Page table User program

20 Loadng Procedure Example Program A Program B Nachos Create thread A wth ts own page table Load Program A nto man memory and setup thread A s page table n AddrSpace::Load( ) Create thread B wth ts own page table Load Program B nto man memory and setup thread B s page table n AddrSpace::Load( ) Put thread A and B nto readylst System start: kernel->machne->run() Load the demanded page run user programs (an nfntve loop) Swtch current thread Page fault Tmer nterrupt occurs

21 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson

22 Related Fles Major Nachos-4./code/machne/machne.cc Nachos-4./code/machne/translate.cc Nachos-4./code/machne/addrspace.cc Nachos-4./code/machne/man.cc Nachos-4./code/machne/nterrupt.cc Nachos-4./code/machne/excepton.cc Mnor Nachos-4./code/machne/mpssm.cc Nachos-4./code/threads/thread.cc Nachos-4./code/threads/scheduler.cc

23 Nachos Page Table The page table s Declared n machne/machne.h Implemented as an array of TranslatonEntry objects. Machne/translate.h class TranslatonEntry { publc: nt vrtualpage; // The page number n vrtual memory nt physcalpage; // The page number n real memory relatve to the start of man memory bool vald; bool readonly; bool use; bool drty; }

24 Machne Class Some mportant varable defntons: const nt PageSze = 8; The page sze of the physcal memory n Nachos const nt NumPhysPages = 8; The number of pages n physcal memory char *manmemory; Physcal memory to store the user program code and data, whle t s executng. TranslatonEntry *pagetable; Pont to the page table of current thread 4

25 AddrSpace Class AddrSpace::AddrSpace( ) The AddrSpace constructor Create an address space to run a user program Set the one to one relatonshp between vrtual pages and physcal pages Clear man memory AddrSpace::~AddrSpace() The AddrSpace destructor Deallocate the page table 5

26 AddrSpace Class (cont.) bool AddrSpace::Load( char *flename) Load a user program nto memory from a fle Nachos assumes vrtual address equals to physcal address The user program s n NOFF format 6

27 AddrSpace Class (cont.) Vod AddrSpace::Execute( ) Run a user program usng the current thread Intalze the regster values of the smulated MIPS machne ths->intregsters(); Set page table regster ths->restorestate(); Jump to the user program kernel->machne->run(); 7

28 AddrSpace Class (cont.) Vod AddrSpace::IntRegsters( ) Set the ntal values for the user-level regster set Vod AddrSpace::RestoreState( ) Tell the machne where to fnd the page table (pagetable) Tell the machne number of pages needed by the user program (numpages) bool AddrSpace::SaveState( ) Save any machne state for ths address space on a context swtch 8

29 Machne Class n translate.cc bool Machne::ReadMem(nt addr, nt sze, nt *value) Read sze (,, or 4) bytes of vrtual memory at addr nto the locaton ponted to by value. If the address translaton (from Machne:: Translate()) s faled, t wll rase an excepton (page fault handlng routne) by nvokng RaseExcepton( ). Arguments: addr the vrtual address to read from sze the number of bytes to read (,, or 4) value the place to wrte the result 9

30 Machne Class n translate.cc (cont.) bool Machne::WrteMem(nt addr, nt sze, nt value) Wrte sze (,, or 4) bytes of the contents of value nto the vrtual memory at locaton address addr. If the address translaton (from Machne::Translaton( )) s faled, t wll rase an excepton by nvokng RaseExcepton( ). Arguments: addr the vrtual address to wrte to sze the number of bytes to be wrtten (,, or 4) value the data to be wrtten drty bt would be set!!

31 Machne Class n translate.cc (cont.) ExceptonType Machne::Translate (nt vrtaddr, nt* physaddr, nt sze, bool wrtng) Translate a vrtual address(vrtaddr) nto a physcal address(*physaddr), usng the current thread s page table. If error, then return the type of the excepton Arguments: vrtaddr the vrtual address to translate *physaddr the place to store the physcal address sze the amount of memory beng read or wrtten wrtng f TRUE, check the read-only bt n the page table to see whether the process attempts to wrte a read only page.

32 Machne Class n mpssm.cc Machne::OneInstructon(Instructon* nstr); Exceute one nstructon from a user program After any excepton or nterrupt, return to kernel ->machne->run() agan Machne::Run() s a loopng functon On a system call, the excepton handler has to ncrement the program counter On an excepton, we don t need to ncrement the program counter n order to restart ths nstructon agan. For example: page fault

33 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson

34 Requrement Multprogrammng and Vrtual Memory(5%) Load multple user programs to run on Nachos smultaneously Implement a pagng mechansm wthout consderng page faults Each user program starts at vrtual address. The system uses nachos default schedulng: swap current user program(thread) out n each tmer nterrupt, whch occurs once every tcks, and swap n the user program wth the specfed order. 4

35 Requrement (cont.) Enable the Loadng of Multple User Programs Modfy man.cc to let t enable loadng three user programs from parameters Ex: >./nachos -x programa programb programc Create one thread for each user program mplement OSPrnt() for test program Modfy AddrSpace::Load( ) to let t Create a page table whle loadng a user program Load a user program nto memory Confgure ts own page table for that user program n each nvocaton. 5

36 Requrement (cont.) Pure demand pagng(%) Intally, load user programs to swap space. Only pages that are demanded n runtme wll be loaded nto man memory. You do need to consder page faults now. Increment kernel->stats->numpagefaults for every page fault You do NOT need to consder page replacement. Report(%) 6

37 Handlng of Page faults In excepton.cc, you have to add the PageFaultExcepton case to load the demanded page. If the replaced page has been modfed or s drty, wrte t back. Don t advance the program counter whle handlng page faults. The system needs to execute the nstructon that causes the page fault. 7

38 Test Programs a.c b.c c.c nt man(){ nt ; for( =;<;++){ OSPrnt( %da\n,); OSPrnt( %da\n,); OSPrnt( %da\n,); OSPrnt( %da\n,); OSPrnt( %da4\n,); OSPrnt( %da5\n,); OSPrnt( %da6\n,); OSPrnt( %da7\n,); OSPrnt( %da8\n,); OSPrnt( %da9\n,); OSPrnt( %da\n,); } } nt man(){ nt ; for( =;<;++){ OSPrnt( %db\n,); OSPrnt( %db\n,); OSPrnt( %db\n,); OSPrnt( %db\n,); OSPrnt( %db4\n,); OSPrnt( %db5\n,); OSPrnt( %db6\n,); OSPrnt( %db7\n,); OSPrnt( %db8\n,); OSPrnt( %db9\n,); OSPrnt( %db\n,); } } nt man(){ nt ; for( =;<;++){ OSPrnt( %dc\n,); OSPrnt( %dc\n,); OSPrnt( %dc\n,); OSPrnt( %dc\n,); OSPrnt( %dc4\n,); OSPrnt( %dc5\n,); OSPrnt( %dc6\n,); OSPrnt( %dc7\n,); OSPrnt( %dc8\n,); OSPrnt( %dc9\n,); OSPrnt( %dc\n,); } } 8

39 Test Program Executon and Output >./nachos -x a b c Output: Loadng program: a Number of pages: 4 Sze of code segment: 656 Vrtual address of code segment: Sze of readonly data segment: 96 Vrtual address of readonly data segment: 656 a a ###ContextSwtch b ###ContextSwtch c 9

40 Hnt In order to support the multprogrammng n Nachos, you need to mplement the excepton handler of SC_Ext snce the system call Ext( ) s nvoked automatcally whle a program completes. 4

41 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson 4

42 Bonus Implement the page replacement usng Enhanced Second-Chance Algorthm. Change NumPhysPages n the machne class to 6. You should consder all PhysPages (or frames) n your man memory altogether, rather than consderng only those PhysPages (or frames) allocated to a certan addrspace. Usng use and drty n class TranslatonEntry Detaled explanaton n your report s requred to get any credt. 4

43 Agenda Motvaton User Programs n Nachos Related Nachos Code for User Programs Project Assgnment Bonus Submsson 4

44 Submsson Make sure your project can be executed over 7 workstaton and prnt message properly. Deadlne: //6 : For the delayed submsson, deduct two ponts for each day. Upload your team project to the FTP ftp server: os/os Pack the whole Nachos-4./code wthout any object fles and your report n a fle named OSPJ_GROUP##.tar.gz The report s lmted to A4 pages. 44

45 Note Do not copy homework. Keep your code secret. On any questons, wrte an e-mal to wth [project] prepend to ttle. 黃柏鈞 : b948@cse.ntu.edu.tw 何建忠 : r999@cse.ntu.edu.tw 陳煒栩 : wsh5angela@hotmal.com 鄭聖威 : r999@cse.ntu.edu.tw Come to R48/R44 durng TA hours 45

46 Thank you!

Virtual Memory. Background. No. 10. Virtual Memory: concept. Logical Memory Space (review) Demand Paging(1) Virtual Memory

Virtual Memory. Background. No. 10. Virtual Memory: concept. Logical Memory Space (review) Demand Paging(1) Virtual Memory Background EECS. Operatng System Fundamentals No. Vrtual Memory Prof. Hu Jang Department of Electrcal Engneerng and Computer Scence, York Unversty Memory-management methods normally requres the entre process