termination suspend (swap-out) executing CPU Scheduling phases (non real-time) pre-emption or cycle done unblock ready, suspended

Transcription

1 76 eal-tme & Embedded Sysems 7 Uwe. Zmmer - The Ausrala aoal Uversy 79 Deployme eal-tme Sysems A schedulg scheme provdes wo feaures: Orderg he use of resources (e.g. PUs, ewors) a lve sysem. Predcg he wors-case behavour of he sysem whe he schedulg algorhm s appled. The predco ca he be used: a comple-ru: o cofrm he overall emporal requremes of he applcao. a ru-: o perm accepace of addoal usagereservao requess. Uwe. Zmmer, The Ausrala aoal Uversy page 79 of 96 (chaper 7: up o page 8) 7 phases (real-) pre-empo or cycle doe bach ready creao admed dspach execug PU ermao ubloc Admace accordg o schedulably Dspachg ad Pre-Empo accordg o deadles, prores, or ules bloced bloc or sychroze Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8) 77 efereces for hs chaper [Burs7] Ala Burs ad Ady Wellgs ocurre ad eal-tme Programmg Ada ambrdge Uversy Press (7) [Murhy] S Murhy, G Mamara esource Maageme eal Sysems ad ewors MIT Press, ambrdge, Massachues, odo, Eglad () Uwe. Zmmer, The Ausrala aoal Uversy page 77 of 96 (chaper 7: up o page 8) 7 Sac versus Dyamc eal-tme Sysems gd: All schedules are se off-le. Full predcably (may hgh egry real- sysems). Sac: Schedule relaos are sacally ordered off-le. Predcable respose o dsurbaces (may real- sysems). Dyamc: Schedules deped o ru- suao. More flexble, more effce (mos sof real- sysems). Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8) 7 Assumpos A smple process model The umber of processes he sysem s fxed. All processes are perodc ad all perods are ow. All processes are depede. The as-swchg overhead s eglgble. All deadles are decal wh he process cycle s (perods). The wors case execuo s ow for all processes. All processes are released a oce. Ths model ca oly be appled o a specfc group of hard real- sysems. (Exesos o hs model wll be dscussed laer hs chaper). Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8) 78 Movao eal-tme Sysems ocurrecy may lead o o-deermsm. o-deermsm may mae harder o predc he mg behavour. eal-tme- schemes reduce o-deermsm. Uwe. Zmmer, The Ausrala aoal Uversy page 78 of 96 (chaper 7: up o page 8) 7 phases (o real-) pre-empo or cycle doe bach ready creao admed dspach execug PU ermao ubloc susped (swap-ou) ready, suspeded susped (swap-ou) swap- bloced, suspeded ubloc swap-ou bloced bloc or sychroze Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8) 7 eal- schedulg Tas se (6, 8) (, ), ), ) Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8)

2 (6, 8) 7 Uwe. Zmmer, The Ausrala aoal Uversy = Maxmal ulzao eal- schedulg: Earles Deadle Frs Uwe. Zmmer, The Ausrala aoal Uversy page 7 of 96 (chaper 7: up o page 8) G ae moooc orderg s opmal ( he framewor of fxed prory schedulers): f a process se s schedulable uder a FPS-scheme, he s also schedulable uder FPS wh rae moooc prores., ) G Sac scheme, sce he order dspach order of processes s fxed ad calculaed off-le. Uwe. Zmmer, The Ausrala aoal Uversy, ) (, ) G Pre-empve scheme. A ru-: dspach he ruable process wh he hghes prory. page 7 of 96 (chaper 7: up o page 8) Uwe. Zmmer, The Ausrala aoal Uversy, ), ) (, ) page 7 of 96 (chaper 7: up o page 8) page 7 of 96 (chaper 7: up o page 8) G If deadles D are decal o cycle s T for each as he: The maxmal ulzao for EDF becomes: T # (suffce ad ecessary es) T, ),, ), ( (, ) (, (6, ( 66, 8) 7 page 77 of 96 (chaper 7: up o page 8) Avod uecessary as swches. Dspach by as d (ou of he currely qualfyg processes). Uwe. Zmmer, The Ausrala aoal Uversy Execue FPS schedule G Fals! Tas se Fxed Prory (FPS), rae moooc eal- schedulg: Fxed Prory (6, 8) 7 page 79 of 96 (chaper 7: up o page 8) G I he example: Wors case respose s are decal o cycle s. Uwe. Zmmer, The Ausrala aoal Uversy eal- schedulg: Fxed Prory page 78 of 96 (chaper 7: up o page 8) espose : Tme from schedule reques o process compleo. G If mulple deadles cocde, oher meas are eeded o selec a process,.e. T, ) Execue EDF schedule G Wors! eal- schedulg: Earles Deadle Frs eal- schedulg. Each process s assged a fxed prory accordg o s cycle : T T & P P 7 Uwe. Zmmer, The Ausrala aoal Uversy Gves a dea how crcal he schedule s. T, ) T, ),, ), ) (6, ( 6, 8) (, ) (, (, ) Wors case respose s Tmes o deadles page 76 of 96 (chaper 7: up o page 8) eal- schedulg: Earles Deadle Frs 79 Uwe. Zmmer, The Ausrala aoal Uversy eal- schedulg: Earles Deadle Frs page 7 of 96 (chaper 7: up o page 8) sce he dspached process s seleced a ru-, due o he curre deadles. G Dyamc scheme, (6, 8) 78 Uwe. Zmmer, The Ausrala aoal Uversy T, ),, ), ( 66, 8) (6, (, ( (, ) G Pre-empve scheme. a. ul fshes. b. ul aoher process deadle s foud earler he he curre oe.. Execue hs process 77, ) Earles Deadle Frs (EDF) Deadles. Deerme (oe of) he process(es) wh he earles deadle. eal- schedulg eal- schedulg 76 (, ) (6, 8) 7

3 , ) = page 7 of 96 (chaper 7: up o page 8) (6, 6) page 78 of 96 (chaper 7: up o page 8) G Ulzao es fals, schedulably o guaraeed. page 76 of 96 (chaper 7: up o page 8) G Ulzao es succeeds, schedulably guaraeed. T = = ( - ) U max = page 76 of 96 (chaper 7: up o page 8) G Ulzao es succeeds, schedulably guaraeed. T = = ( - ) U max Uwe. Zmmer, The Ausrala aoal Uversy U T, ),, ) (, ) (, = (6, ) 76 = page 76 of 96 (chaper 7: up o page 8) G Ulzao es succeeds, schedulably guaraeed. T = = ( - ) U max Uwe. Zmmer, The Ausrala aoal Uversy U, ), ) (, ) page 79 of 96 (chaper 7: up o page 8) G Ulzao es fals, schedulably o guaraeed. 6 T = =.87 >.779. ( - ) U max Uwe. Zmmer, The Ausrala aoal Uversy U, ) Execue FPS schedule G Wors!, ) Execue FPS schedule G Wors! (66, ) (6, 76 6 T = =.87 >.779. ( - ) U max (, ) Furher reduced as se = Uwe. Zmmer, The Ausrala aoal Uversy U T, ) page 76 of 96 (chaper 7: up o page 8) G Ulzao es fals, schedulably o guaraeed. Uwe. Zmmer, The Ausrala aoal Uversy 79 T = >.779. ( - ) U max eal- schedulg: Fxed Prory Uwe. Zmmer, The Ausrala aoal Uversy U 6 = eal- schedulg: Fxed Prory, ) U eal- schedulg: Fxed Prory page 77 of 96 (chaper 7: up o page 8) (, ) (6, ) G Ulzao es fals, schedulably o guaraeed. Uwe. Zmmer, The Ausrala aoal Uversy 76 6 T = =.87 >.779. ( - ) U max,,, ), ) (6, (66, 6) = Execue FPS schedule G Wors! 9 Execue FPS schedule G Wors! ((, (,, )) U umber of processes, ), ) (, ) educed as se (6, 8) eal- schedulg: Fxed Prory 78, ) T # ( - ) U max G Suffce, ye o ecessary es Uwe. Zmmer, The Ausrala aoal Uversy..6 page 7 of 96 (chaper 7: up o page 8) (, ) = wh he compuao ad T he legh of he perod for as ou of ass ad assumg ha he deadle D = T U Execue FPS schedule G Fals! Maxmal ulzao eal- schedulg: Fxed Prory eal- schedulg: Fxed Prory eal- schedulg: Fxed Prory 76 eal- schedulg: Fxed Prory 7 (6, 6) 77 Uwe. Zmmer, The Ausrala aoal Uversy, ) (, ), ) Execue FPS schedule G Fals! eal- schedulg: Fxed Prory (6, 8) 7 Maxmal uly

4 76 eal- schedulg: Fxed Prory Wors case respose s (6, ) (, ), ), ) for he hghes prory as: = Uwe. Zmmer, The Ausrala aoal Uversy page 76 of 96 (chaper 7: up o page 8) 766 eal- schedulg: Fxed Prory espose aalyss T = + e o $ > Fxed -po equao + ecurre form: = + f p $ wh: = > T + Ierae he recurre form ul: = + or > D Uwe. Zmmer, The Ausrala aoal Uversy page 766 of 96 (chaper 7: up o page 8) 769 eal- schedulg: Earles Deadle Frs espose aalyss () () a T a a a+ T- T = ; + E + * f p T, * > H T +! m max $ Fxed -po equao ecurre form: () + () a T a a a+ T- T = ; + E + * f p T, *, > H T +! m max $ wh: = a + + Ierae ul: () a = () a + or () a > a+ D Uwe. Zmmer, The Ausrala aoal Uversy page 769 of 96 (chaper 7: up o page 8) 76 eal- schedulg: Fxed Prory Wors case respose s (6, ) (, ), ), ) for ohers ass: = + I (erferece from hgher prory ass) Uwe. Zmmer, The Ausrala aoal Uversy page 76 of 96 (chaper 7: up o page 8) 767 eal- schedulg: Earles Deadle Frs espose aalyss The wors case for Earles Deadle Frs s o ecessarly whe all ass are released a oce! All possble release combaos a full hyper-cycle eed o be cosdered! The respose s are bouded by he cycle s as log as he maxmal ulzao s #. Oher ass eed o be cosdered oly, f her deadle s closer or equal o he curre as. Uwe. Zmmer, The Ausrala aoal Uversy page 767 of 96 (chaper 7: up o page 8) 77 eal- schedulg: Earles Deadle Frs espose aalyss () () a T a a a+ T- T = ; + E + * f p T, * > H T +! m max $ Fxed -po equao = max " () a - a, a! A where A = scm ( T ) Uwe. Zmmer, The Ausrala aoal Uversy page 77 of 96 (chaper 7: up o page 8) 76 eal- schedulg: Fxed Prory Wors case respose s (6, ) (, ), ), ) for ohers ass: = + e o $ > T Uwe. Zmmer, The Ausrala aoal Uversy page 76 of 96 (chaper 7: up o page 8) 768 eal- schedulg: Earles Deadle Frs espose aalyss () () a T a a a+ T- T = ; + E + * f p T, > H T +! m $ Uwe. Zmmer, The Ausrala aoal Uversy page 768 of 96 (chaper 7: up o page 8) 77 eal- schedulg: Fxed Prory Wors case respose s (6, ) (, ), ), ) = # ; = # ; = # 6 ; T # ( - ) = Uwe. Zmmer, The Ausrala aoal Uversy page 77 of 96 (chaper 7: up o page 8),,

5 ; = # T # = = T # T "^T, h, = "^6, 6h, ^, h, ^, h, Uwe. Zmmer, The Ausrala aoal Uversy "^T, h, = "^6, h, ^, h, ^, h, # ( - ) = Ulzao Tes > e ",,, ",,, o T $ " #,,, + espose Tmes ", T # max ", 6,, ", 8,, " 6,,, $ (a) - a.a! A page 778 of 96 (chaper 7: up o page 8) = espose Tmes ", Earles Deadle Frs Ulzao Tes G EDF ca hadle hgher (full) ulzao ha FPS. Uwe. Zmmer, The Ausrala aoal Uversy page 779 of 96 (chaper 7: up o page 8) G EDS: O() ulzao es respose aalyss: fxed po equao hyper-cycle G FPS: O() ulzao es respose aalyss: fxed po equao espose aalyss ad ulzao ess: G EDF: ay process ca mss s deadle G ad ca rgger a cascade of faled deadles. G FPS: processes wh lower prores wll always mss her deadles frs. Graceful degradao (resource s over-booed): G FPS s easer o mpleme ad mples less ru- overhead ; = 6 # Tass are perodc 78 Uwe. Zmmer, The Ausrala aoal Uversy = #, ) ; = # 6 Uwe. Zmmer, The Ausrala aoal Uversy Wors case execuo s are ow Pre-empve schedulg T # page 78 of 96 (chaper 7: up o page 8) Deadles are decal wh as s perod (D = T ) Tass are depede = page 777 of 96 (chaper 7: up o page 8) ; Wors case respose s eal- schedulg: Earles Deadle Frs page 77 of 96 (chaper 7: up o page 8) Smplsc Assumpos Fxed Prory, ) Fxed Prory Earles Deadle Frs page 776 of 96 (chaper 7: up o page 8) ; (, ) (6, ) espose Tme Aalyss ; = # GTesg all combaos a hyper-cycle: = max " (a) - a,a! A where A = scm ) eal-world Exeso 779 ; = 8 # Uwe. Zmmer, The Ausrala aoal Uversy = #, ) Wors case respose s eal- schedulg: omparso ; page 77 of 96 (chaper 7: up o page 8) ; = 6 # 6 eal- schedulg: Earles Deadle Frs Uwe. Zmmer, The Ausrala aoal Uversy T, ),, ), (, ( (, ) ( 66, 8) (6, 77 eal- schedulg: omparso "^T, h, = "^6, 8h, ^, h, ^, h, 778 ; = # Uwe. Zmmer, The Ausrala aoal Uversy = # (,, ),, ) T, ) (6, ( 6) ( (, ) (, ) (, Wors case respose s page 77 of 96 (chaper 7: up o page 8) Wors case respose s 776 Uwe. Zmmer, The Ausrala aoal Uversy ; = # ; = 9 6 ; T ( - ) = eal- schedulg: Earles Deadle Frs page 77 of 96 (chaper 7: up o page 8) = #, ) eal- schedulg: Earles Deadle Frs ; = # 6 ; T ( - ) = (6, (66, 8) 77 Uwe. Zmmer, The Ausrala aoal Uversy = #, ), ), ) (, ) (6, 8) Wors case respose s Wors case respose s ( ) (, eal- schedulg: Fxed Prory eal- schedulg: Fxed Prory 77 ( 6) (6, 77

6 G we wll roduce (brefly) cooperave schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 787 of 96 (chaper 7: up o page 8) Seg a deferrable server as as a proxy for sporadc aperodc ass o hghes prory level., ) Uwe. Zmmer, The Ausrala aoal Uversy page 788 of 96 (chaper 7: up o page 8) G Hard real- ass are sll schedulable wh he server as deployg s full legh. T, ),,, ) -, ) - page 78 of 96 (chaper 7: up o page 8) FPS server as as ormal as (66, 7) ( (6, 788 Uwe. Zmmer, The Ausrala aoal Uversy Sporadc aperodc as se o lowes prory., ) Iroducg g a server as o hghes g p proryy page 78 of 96 (chaper 7: up o page 8) Sporadc ad Aperodc Processes Sporadc ad Aperodc Processes (6, 7) 787 Uwe. Zmmer, The Ausrala aoal Uversy, ), ) (, ) (6, 7) Iroducg g a sof real- as page 78 of 96 (chaper 7: up o page 8) G we wll roduce faul olera schedulg FPS for hard real- ass, ) G we wll roduce (brefly) cooperave schedulg Sporadc ad Aperodc Processes 78 Uwe. Zmmer, The Ausrala aoal Uversy G we wll roduce arbrary deadles G we wll roduce schedules for eracg ass Wors case execuo s are ow Pre-empve schedulg Tass are depede Sporadc ad Aperodc Processes page 78 of 96 (chaper 7: up o page 8) G we wll roduce faul olera schedulg G we wll roduce sporadc ad aperodc processes Deadles are decal wh as s perod (D = T ) (6, 7) 78 Uwe. Zmmer, The Ausrala aoal Uversy G we wll roduce arbrary deadles G we wll roduce schedules for eracg ass Wors case execuo s are ow Pre-empve schedulg Tass are depede Deadles are decal wh as s perod (D = T ) G we wll roduce sporadc ad aperodc processes G More ealsc Assumpos Tass are perodc G More ealsc Assumpos eal-world Exeso 78 eal-world Exeso Tass are perodc 78 - Uwe. Zmmer, The Ausrala aoal Uversy page 789 of 96 (chaper 7: up o page 8) Deferrable server as oly deployg f here are requess from he sporadc aperodc as. Sporadc as ulzg deferrable server page 786 of 96 (chaper 7: up o page 8) Sporadc ad Aperodc Processes G Schedule mus also wor wll less erferece. T, ) (,, ) ( 66, 7) (6, (, (, ) 789 G espose s for sporadc aperodc as ca be large. Uwe. Zmmer, The Ausrala aoal Uversy FPS lowes prory for sof real- as Sporadc ad Aperodc Processes page 78 of 96 (chaper 7: up o page 8) Sporadc aperodc as does o erfere wh hard real- ass. T, ), ) (6 (6, 7) (, ) ( 786 Uwe. Zmmer, The Ausrala aoal Uversy, ), ) Hard real- ass Sporadc ad Aperodc Processes (6, 7) 78

7 Sporadc as ulzg EDF server Sporadc ad Aperodc Processes page 79 of 96 (chaper 7: up o page 8) Tass wh D < T (Deadle earler ha cycle ) page 796 of 96 (chaper 7: up o page 8) Ay as se Q whch s schedulable by a FPS scheme W, s also schedulable uder DMPO. Deadle Moooc Prory Orderg (DMPO) ae Moooc Prory Orderg (MPO) Uwe. Zmmer, The Ausrala aoal Uversy emma: o: hage from: page 79 of 96 (chaper 7: up o page 8) Tass wh arbrary deadles I case of fxed prory schedulg (FPS): 796 Uwe. Zmmer, The Ausrala aoal Uversy G Swf respose s for he sporadc aperodc ass wh deadles pushed o her lms. T, ),, ), ((6, ( (6 66, 7)) (, (,, ) 79 Uwe. Zmmer, The Ausrala aoal Uversy G Mmal er-arrval-s owledge s employed. G Ierferece level less or equal o a deferrable server. A sporadc server oly repleshes afer a fxed afer s acual deployme. orad aad dc d Server Hard Sporadc, ),,, ) Sporadc as ulzg sporadc server Sporadc ad Aperodc Processes (( 66, 7) (6, ((, (, ), 79 ED ED ED Iroducg g a EDF server Sporadc ad Aperodc Processes eal-world Exeso page 79 of 96 (chaper 7: up o page 8) G we wll roduce (brefly) cooperave schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 797 of 96 (chaper 7: up o page 8) G Wl: erferes oly oce wh G l = # D D & l D W: # D D # T & T meag ha erfered oly oce wh also: released oce, ad c. s schedulable Wl because: b. s schedulable Wl because Pl > P & l # # D & l # D a. All! Q wh P P or P P are uaffeced.. Wl schedules Q because:. Geerae Wl by swappg P ad P G _ P l P l _ D D G DMPO D T W Uwe. Zmmer, The Ausrala aoal Uversy W: D D # T & D T D T page 798 of 96 (chaper 7: up o page 8) Swap p wo p prores ou of W whch volae DMPO: Swap wo prores ou of W whch volae DMPO: page 79 of 96 (chaper 7: up o page 8) G we wll roduce faul olera schedulg Proof of DMPO opmaly 798 Uwe. Zmmer, The Ausrala aoal Uversy G we wll roduce arbrary deadles G we wll roduce schedules for eracg ass Wors case execuo s are ow Pre-empve schedulg Tass are depede Deadles are decal wh as s perod (D = T ) G we wll roduce sporadc ad aperodc processes G More ealsc Assumpos Tass are perodc 79 Uwe. Zmmer, The Ausrala aoal Uversy The EDF equvale o a deferrable server: a perodc server as wh a mmedae deadle., ), ) (6, 7) 79 Proof of DMPO opmaly page 79 of 96 (chaper 7: up o page 8)., are wo ass Q wh P P ad D D W G JDMPO 797 Uwe. Zmmer, The Ausrala aoal Uversy G Deadles explcly pushed o her lms durg he ED phases. ED Earles Deadle as (ED) for sporadc ass Sporadc ad Aperodc Processes page 79 of 96 (chaper 7: up o page 8) Earles Deadle as schedulg (whle sll eepg all deadles) whe sporadc aperodc ass are o be scheduled., ) (,,, ) ( 66, 7)) ( (6 (6, (, ( (, ) 79 Uwe. Zmmer, The Ausrala aoal Uversy G Pushes he hard real- ass o her deadles. Sar he sporadc aperodc ass o hgh prory ad demoe hem for he hard real- ass o complee (G dyamc schedulg scheme). T, ),, ) (, (, ) (, (, ) FPS wh dual prores Sporadc ad Aperodc Processes (6, 6 7) 7 (6, 79 orad o raaad dcc d Sporadc Hard Spo Server Hard Sporadc

8 799 Proof of DMPO opmaly Swap wo prores ou of W whch volae DMPO: W T T D D W: # D D # T & T erfered oly oce wh also: released oce, ad Uwe. Zmmer, The Ausrala aoal Uversy page 799 of 96 (chaper 7: up o page 8) 8 Proof of DMPO opmaly Swap all prores ou of W whch volae DMPO: Swap all, Q, wh _ P > P _ D > D W resulg all, Q wh P > P o have D < D osug he DMPO scheme Sce each swappg operao eep schedulably, he resulg DMPO scheme s also schedulable. Deadle moooc orderg s opmal: (f a process se s schedulable uder a FPS-scheme, he s also schedulable uder FPS wh deadle moooc prores.) Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 eal-world Exeso More ealsc Assumpos Tass are perodc we wll roduce sporadc ad aperodc processes Deadles are decal wh as s perod (D = T ) Tass are depede Pre-empve schedulg Wors case execuo s are ow we wll roduce arbrary deadles we wll roduce schedules for eracg ass we wll roduce (brefly) cooperave schedulg we wll roduce faul olera schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Proof of DMPO opmaly Swap wo prores ou of W whch volae DMPO: W W' T T T T D D D D W: # D D # T & T erfered oly oce wh also: released oce, ad Wl: Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Tass wh arbrary deadles Tass wh D > T (Deadle laer ha cycle ) Assumpo: every as s released oly afer he former release of s compleed. I case ha > T for a specfc schedulg suao, he followg release of as s delayed by - T. Md ha > T cao hold for all release suaos, oherwse he as s o schedulable. The wors case respose ^ h mgh hus be loger ha T bu mus sll be shorer ha D. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 86 Idepede ass 8, 8), ) (6, ), ) Deadles decal o cycle s DMPO or MPO. Uwe. Zmmer, The Ausrala aoal Uversy page 86 of 96 (chaper 7: up o page 8) 8 Proof of DMPO opmaly Swap wo prores ou of W whch volae DMPO: W W' T T T T D D D D ' ' W: # D D # T & T erfered oly oce wh also: released oce, ad Wl: erferes oly oce wh l= # D D & l D Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Tass wh arbrary deadles Tass wh D > T (Deadle laer ha cycle ) Assumpo: every as s released oly afer he former release of s compleed. Sce he respose ca ow be poeally greaer ha he cycle T: more ha oe release q of he as eeds o be cosdered: ( q) = B+ q+ e ( q) T o where 6 q q) -( q- ) T # D ( > B s he blocg ; q s he umber of releases. = % ( q) - ( q - ) T q! " f q max, ad max ( q) qmax = ' q q # T Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 87 Idepede ass 8, 8), ) (6, ), ) Schedulable uder DMPO or MPO. Uwe. Zmmer, The Ausrala aoal Uversy page 87 of 96 (chaper 7: up o page 8)

9 88 Tas depedeces 8, 8), ) (6, ), ) oc requess by wo ass. Uwe. Zmmer, The Ausrala aoal Uversy page 88 of 96 (chaper 7: up o page 8) 8 Prory herace Maxmal blocg for as : B = usage (,) r () r wh: deog he umber of crcal secos. usage (,) r beg a boolea fuco reurg for rue ad dcag he r s used by: a leas oe wh P < P ad a leas oe wh P $ P () r deog he wors case compuao crcal seco r Each as ca oly be bloced oce for each employed resource! Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Tas depedeces wh mulple locs 8, 8), ) (6, ), ) Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 89 Tas depedeces 8, 8), ) (6, ), ) The lower prory as blocs he hgher prory as. (oe ha he blue as s uaffeced.) Prory verso Uwe. Zmmer, The Ausrala aoal Uversy page 89 of 96 (chaper 7: up o page 8) 8 Prory herace 8, 8), ) (6, ), ) The lower prory as s promoed o he prory of he bloced as. The as o prory s bloced due o prory herace. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Tas depedeces wh mulple locs 8, 8), ) (6, ), ) by DMPOMPO resuls blocg for he hgher prory ass. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Prory herace Tas hers prory P of as f:. P < P.. Tas has loced a resource Q.. Tas s bloced wag for he release of resource Q. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Whou prory herace 8, 8), ) (6, ), ) The lower prory as blocs he hgher prory as. (oe ha he blue as s uaffeced.) Prory verso Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 86 Tas depedeces wh mulple locs 8, 8), ) (6, ), ) by DMPOMPO wh prory herace does o mprove he resul. Uwe. Zmmer, The Ausrala aoal Uversy page 86 of 96 (chaper 7: up o page 8) r

10 87 rcular as depedeces 8, 8), ) (6, ), ) Uwe. Zmmer, The Ausrala aoal Uversy page 87 of 96 (chaper 7: up o page 8) 8 elg Prory Proocol 8, 8), ) (6, ), ) Avods he deadloc! Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 eal-world Exeso More ealsc Assumpos Tass are perodc we wll roduce sporadc ad aperodc processes Deadles are decal wh as s perod (D = T ) Tass are depede Pre-empve schedulg Wors case execuo s are ow we wll roduce arbrary deadles we wll roduce schedules for eracg ass we wll roduce (brefly) cooperave schedulg we wll roduce faul olera schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 88 rcular as depedeces 8, 8), ) (6, ), ) by DMPOMPO resuls deadloc. (Prory herace does o mae a dfferece for bloced ass.) Uwe. Zmmer, The Ausrala aoal Uversy page 88 of 96 (chaper 7: up o page 8) 8 Immedae celg prory proocol (POSIX, Ada, T-Java) Implcaos: Tass are dspached oly f all employed resources are avalable. Deadlocs are preveed (o hold ad wa). umber of coex swches are reduced. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 o pre-empve schedulg I pre-empve schedulg: Maxmal dvdual blocg s B ca be deermed for each as by employg a prory celg proocol. Maxmum overall blocg Bmax = max # B -. ooperave Every as s dvded o pre-empve blocs of # B max. All crcal secos are compleely eclosed a sgle bloc. Every as calls a de-schedulg roue a he ed of each bloc,.e. offerg a as swch. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 89 Immedae celg prory proocol (POSIX, Ada, T-Java) Each as has a sac prory P. Each resource has a sac celg prory : = max # employ ^ h$ P- wh employ (, ) beg a boolea fuco reurg for rue f as employs resource. Each as has a dyamc prory P D : P D = max # P, max # loced ^, h$ - - wh loced (, ) beg a boolea fuco reurg for rue f as holds resource. Uwe. Zmmer, The Ausrala aoal Uversy page 89 of 96 (chaper 7: up o page 8) 8 Immedae celg prory proocol (POSIX, Ada, T-Java) Maxmal blocg : B = max # usage(,) r $ () r - r = deog he umber of crcal secos. usage (,) r beg a boolea fuco reurg for rue ad dcag ha r s used by: a leas oe wh P < P. () r deog he wors case compuao crcal seco r Each as ca oly be bloced oce by oe lower prory as! Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 o pre-empve schedulg ooperave Implcaos: umber of as swches s reduced. aches, pre-fechg, ad ppeles are more effce. Execuo s are (a b) easer o predc. Schedules are smpler. Ierdepede as ses are schedulable deadloc free by desg. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8),

11 86 o pre-empve schedulg ooperave espose s: = + F wh + B F = max f T p > wh F he execuo of he fal bloc. For he smplfed case of = = = F = Bmax : = + wh = + f T p > For he furher smplfed case of 6 T : = T : = + > Uwe. Zmmer, The Ausrala aoal Uversy page 86 of 96 (chaper 7: up o page 8) 89 Faul Tolerace Excepos ad ecoveres f Tas eeds exra PU- for error recovery or excepo hadlg ad he mmum er-arrval bewee fauls s T f : = B + + e T o + ) d T > max $ If error recovery s performed a he hghes prory: = B + + e T o + ) d T > max Uwe. Zmmer, The Ausrala aoal Uversy page 89 of 96 (chaper 7: up o page 8) 8 aguage suppor Ada provdes: Tas ad errup prores (sac, dyamc, acve). Tas arbues. Prorzed ery queues. Prory celg locg (IPP). Schedulers (FPS wh FIFO wh prores (pre-empve), oud ob, EDF). Tas execuo measuremes. Sporadc servers Ada does currely o provde: Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 87 o pre-empve schedulg ooperave osderaos: ode bloc dvso eed o be doe horoughly. Addoal proeco agas msbehavg (o-cooperave) ass: Scheduler pre-emps ass (deferred pre-empo), whch fal o offer a de-schedule hemselves. Due o a ceral B max, addoal ass eed o be egeered o parcpae a specfc cooperave schedule. equres ha a value B max ca be acceped by all ass. Shor ad reacve ass are excluded or reaed separaely. Uwe. Zmmer, The Ausrala aoal Uversy page 87 of 96 (chaper 7: up o page 8) 8 eal-world Exeso More ealsc Assumpos Tass are perodc we wll roduce sporadc ad aperodc processes Deadles are decal wh as s perod (D = T ) Tass are depede Pre-empve schedulg Wors case execuo s are ow we wll roduce arbrary deadles we wll roduce schedules for eracg ass we wll roduce (brefly) cooperave schedulg we wll roduce faul olera schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 Ada pacage Sysem s subype Ay_Prory s Ieger rage mplemeao-defed; subype Prory s Ay_Prory rage Ay_Prory Frs.. mplemeao-defed; subype Ierrup_Prory s Ay_Prory rage Prory as +.. Ay_Prory as; Defaul_Prory : cosa Prory := (Prory Frs + Prory as) ; ed Sysem; pacage Ada.Dyamc_Prores s procedure Se_Prory (Prory : Sysem.Ay_Prory; T : Ada.Tas_Idefcao.Tas_ID := Ada.Tas_Idefcao.urre_Tas); fuco Ge_Prory ( T : Ada.Tas_Idefcao.Tas_ID := Ada.Tas_Idefcao.urre_Tas) reur Sysem.Ay_Prory; ed Ada.Dyamc_Prores; Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 88 eal-world Exeso More ealsc Assumpos Tass are perodc we wll roduce sporadc ad aperodc processes Deadles are decal wh as s perod (D = T ) Tass are depede Pre-empve schedulg Wors case execuo s are ow we wll roduce arbrary deadles we wll roduce schedules for eracg ass we wll roduce (brefly) cooperave schedulg we wll roduce faul olera schedulg Uwe. Zmmer, The Ausrala aoal Uversy page 88 of 96 (chaper 7: up o page 8) 8 Geeral schedulg mehods Some as ses ca be scheduled by roducg offses o he release s, ye Whou ay furher resrcos hs problem s P-hard By roducg furher assumpos abou cycle graulary ad assocaed deadles: Schedulably aalyss complexy ca be reduced o polyomal. e.g. esrc cycle s o powers of wo of a base. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) 8 aguage suppor POSIX provdes: Threads ad errup prores (sac, dyamc, acve). Threads ca be sysem coeed or process coeed (prory schedulg uclear hs case). Prorzed message queues. Prory celg locg (IPP). Schedulers, prory based wh a leas: FIFO, oud-ob, Sporadc Server, possbly ohers. Tmers. Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8) f f f f

12 8 Summary Basc real- schedulg Fxed Prory (FPS) wh ae Moooc (MPO) ad Deadle Moooc Prory Orderg (DMPO). Earles Deadle Frs (EDF). eal-world exesos Aperodc, sporadc, sof real- ass. Deadles dffere from perod. Sychrozed als (prory herace, prory celg proocols). ooperave ad deferred pre-empo schedulg. Faul olerace erms of excepo hadlg cosderaos. aguage suppor Ada, POSIX Uwe. Zmmer, The Ausrala aoal Uversy page 8 of 96 (chaper 7: up o page 8)