The Design, Implementation and Initial Evaluation of an Advanced Knowledge-based Process Scheduler

Transcription

1 Th Dign, Implmntation and Initial Evaluation of an Advancd Knowldg-bad roc Schdulr Sukanya Suranauwarat Hido Taniguchi Graduat School of Information Scinc and Elctrical Enginring, Kyuhu Univrity, Fukuoka-hi, , Japan Abtract Traditional oprating ytm control th xcution of program rgardl of how oftn thy ar run. Thi rai th qution: can't th oftn run or th oftn ud program provid bttr prformanc if an oprating ytm had an ability to optimiz thir xcution bhavior bad on a knowldg th oprating ytm had obtaind from thir prviou xcution()? In thi papr, w intgrat thi ability into a part of an oprating ytm calld a proc chdulr and xamin it cot and bnfit. Our initial valuation how that th cot involvd in our chdulr i mall and th procing tim can b rducd by uing thi chdulr.. Introduction Traditional oprating ytm control th xcution of program rgardl of how oftn thy ar run. In othr word, with traditional oprating ytm, th oftn ud program ar tratd in th am way a tho that ar rarly run or tho that ar run for th firt tim. Howvr, among th program that ar in xcution, it i dirabl for ur to hav thir oftn ud program to b xcutd at th hight pd. Thrfor, in thi papr, w ak whthr th oftn ud program might provid bttr prformanc if an oprating ytm had an ability to optimiz or to altr thir xcution bhavior bad on an advancd knowldg a knowldg th oprating ytm obtaind from th prviou xcution() of th program. So, w dcidd to intgrat thi ability into a part of an oprating ytm calld a proc chdulr, and w dign a chdulr that altr th xcution bhavior of a program by changing th timing of proc witching. Mor pcifically, our chdulr dlay proc witching in ordr to allow a proc running on bhalf of an oftn ud program to continu it xcution vn though it tim-lic ha alrady xpird, whn it i prdictd from an advancd knowldg that that proc nd a littl bit mor CU tim bfor it voluntarily rlinquih th CU. By doing thi, w can achiv nhancd prformanc. A a concrt xampl, by dlaying proc witching of an objctiv proc that u up it tim-lic jut bfor it initiat an I/O opration, it procing tim and proc witching cot can b rducd. Sinc it do not nd to wait until it nxt tim-lic to initiat an I/O opration and rlinquih th CU

2 immdiatly aftr that for th I/O compltion. A mntiond, th dciion about whthr or not to dlay th proc witching i dtrmind bad on an advancd knowldg, which w will call FS (rogram Flow Squnc). Th FS of ach program i cratd bad on th xcution bhavior of it corrponding proc at th nd of th firt xcution, and it i ud whnvr th program i xcutd from thn on. It i alo adjutd bad on th fdback obtaind from ach xcution. W implmnt our chdulr in BSD/OS 2. and valuat it ffctivn xprimntally. Our initial xprimntal rult how that th cot involvd in our chdulr i mall and th procing tim can b rducd by uing our chdulr. Th rt of thi papr i organizd a follow. Sction 2 dicu rlatd work. Sction 3 and Sction 4 dcrib th dign and implmntation of our chdulr rpctivly. Sction 5 dcrib our xprimnt and xplain th rult w obtaind. Sction 6 offr our concluion and futur work. 2. Rlatd Work Th work dcribd in thi papr rlat mainly to th ara of CU chduling in oprating ytm. Traditional proc chdulr in oprating ytm control th haring of th CU rourc among proc uing a fixd chduling policy bad on th utilization of a computr ytm uch a a ral-tim or a tim-haring ytm. Ral-tim ytm chdulr ar uually only availabl in ral-tim oprating ytm, and not in gnral-purpo oprating ytm in which tim-haring ytm chdulr ar ud. In othr word, ral-tim and tim-haring ytm chdulr hav xitd in two parat world. Howvr, th advnt of multimdia application on C and worktation ha calld for nw chduling paradigm to upport ral-tim in ytm with convntional tim-haring chdulr. On impl approach to do thi, which ha bn adoptd by many gnral-purpo oprating ytm uch a Solari, Linux and Window NT, i to provid fixd prioriti to ral-tim application [][2]. Anothr approach i to chdul bad on proportion and/or priod [3][4][5][6]. Anothr approach i bad on hirarchical chduling with vral chduling cla and with ach application bing aignd to on of th cla for th ntir duration of it xcution [7][8][9]. Howvr, non of th abov approach i trying to chdul bad on contnt or bhavior of a proc, which i what our approach do. A a conqunc, in om ca, thi can hindr an ffctiv u of th CU rourc or can xtnd th procing tim of a proc unncarily. For xampl, in a tim-haring ytm, if th proc i till running at th nd of it tim-lic, th CU i prmptd and givn to th nxt waiting proc no mattr how much mor CU tim th proc nd. Thu, a proc that nd jut a littl bit mor CU tim will alo nd to wait until it nxt tim-lic. Bcau of thi, th procing tim and th proc witching cot incra unncarily. For xampl,

3 whn a proc u up it tim-lic jut bfor it initiat an I/O opration, it will voluntarily rlinquih th CU (i.., th proc block itlf pnding th compltion of th I/O opration) immdiatly aftr th bginning of it nxt tim-lic. If w had prdictd th bhavior of th proc and dlayd proc witching according to th prdictd bhavior allowing th proc to continu it xcution until it initiatd an I/O opration, thn th xtra cot mntiond abov would hav bn avoidd. In a paralll computr ytm, chduling a paralll program onto CU i baically don bad on bhavior of proc by taking a dirctd acyclic graph rprnting th xcution bhavior of th paralll program (.g., dpndnci of cod gmnt) a input, and chdul it onto CU of a targt machin in a mannr which rduc th compltion tim [0][][2]. Howvr, chduling i prformd without rgard to th prviou xcution bhavior of th paralll program a our approach do. In addition to proc chduling, on function in Window 98, which ur can gt fatr program tart up a a prformanc nhancmnt [3], u an ida imilar to our. That i, th function improv th prformanc of a ur' program bad on th prviou uag of th program. To b mor pcific, th function crat a log fil to dtrmin which program a ur run mot frquntly. All uch frquntly ud fil ar thn placd in a ingl location on th ur' hard dik, which furthr rduc th tim ndd to tart tho program [4]. Howvr, th function do not altr th xcution bhavior of program bad on th prviou uag, which i what our ida do. Thrfor, by uing th function in Window 98, th oprating ytm can control a ur' program mor fficintly until a ur' program tart up (i.., th oprating ytm can locat and load a ur' program fatr), but it cannot xcut or run a ur' program mor fficintly. 3. Dign Our ida-bad chdulr can b dividd in two part: th loggr and th proc controllr. Whn a program i xcutd, if it FS do not xit thn th loggr will rcord th xcution bhavior of th corrponding proc and u it to crat FS of th program at th nd of th xcution. If it FS xit thn th proc controllr will altr th xcution bhavior of th corrponding proc bad on FS, which in thi papr man that it will mak a dciion about whthr or not th proc witching hould b dlayd bad on th FS, whn th corrponding proc i running at th nd of it tim-lic. Th proc controllr alo adjut FS to chang in xcution bhavior of a program. Not that, in thi papr, w dicu only th program that conit of a ingl proc in which th mutual rlation btwn proc in th am program i not a concrn. Figur i a impl xampl ud to idntify how our chdulr work and how it improv th prformanc. In thi figur, proc A and proc B nd rpctivly 3.4 cond and 2. cond of CU

4 tim to complt thir job. Both proc hav th am priority and a tim-lic of cond. Figur (a) and (b) how th procing tim of proc A and proc B whn uing a convntional timharing chdulr and whn uing our chdulr rpctivly. In Figur (a), th procing tim of proc A and proc B ar 5.5 cond and 4. cond rpctivly, whil in Figur (b), bad on th advancd knowldg, FS, that proc B nd only 0. cond mor CU tim to complt it job, th chdulr dlay proc witching by 0. cond to allow proc B to complt it job. Dlaying proc witching cau th procing tim of proc B to b rducd to 3. cond whil that of proc A i till th am a in Figur (a). Morovr, th numbr of proc witch of th proc B dcra from 6 to 4. tim-lic proc A proc B cond 5.5 cond 4. cond (a) normal proc witching tim-lic cond 0. cond dlay proc A proc B 5.5 cond 3. cond (b) dlayd proc witching Figur : A chduling xampl. Th following ction dicu th part of our chdulr in mor dtail. 3. Th Loggr Whn a program i xcutd, if it FS do not xit thn a log about th corrponding proc i collctd rcording th information ncary to crat FS. A log (hown in Figur 2(a)) i a qunc of ntri dcribing tim, proc idntifir and proc tat. Thi information i rcordd at dipatch tim, i.., whn dciding which proc to run nxt. Not that thr ar many proc tat, but w will focu only on run, rady, and wait tat. A proc i aid to b running in th run tat if it i currntly uing th CU. A proc i aid to b rady in th rady tat if it could u th CU if it wr availabl. A proc i aid to b blockd in th wait tat if it i waiting for om vnt to happn (.g., an I/O compltion vnt) bfor it can procd.

5 Nxt, uing th log mntiond abov crat FS. A FS (hown in Figur 2(b)) i compod of th program nam and a qunc of it proc information, i.., a qunc of ntri dcribing proc tat and tim pnt. W will rfr to ach tim pnt in th run tat a a CU tim of FS ( T ). (a) a log (b) a FS program nam tim proc idntifir a log ntry proc tat proc tat a FS ntry tim pnt Figur 2: Th imag of a log and a FS. 3.2 Th roc Controllr Whn a proc i running at th nd of it tim-lic, if th FS of th program it run on bhalf of xit, thn th dciion about whthr proc witching hould b dlayd or not i dtrmind bad on FS a follow. T C C T, thn th proc i allowd to continu uing th CU, () If ( c ) m T C C > T, thn th nxt waiting proc i dipatchd, (2) If ( c ) m whr C c i th currnt tim, C i th tim that a proc tart uing th CU for ach allocatd portion of CU, T i th xpctd CU tim a proc would u from C until it voluntarily rlinquih th CU (ach T i dtrmind bad on ach CU tim of FS ( T )) and T m i th maximum tim to dlay proc witching, calld maximum dipatch dlay tim. According to thi, whn a proc i running at th nd of it tim-lic, if th xpctd CU tim th proc would u from now until it voluntarily rlinquih th CU i mallr than th maximum dipatch dlay tim T m, thn w allow th proc to continu uing th CU intad of dipatching th nxt waiting proc. W not that tting th T m arbitrarily will cau th managmnt of proc witching to bcom complx, o w nforc th rul that T m mut b a multipl of timlot whr timlot i th minimum unit of tim that proc witching can b dlayd. Sinc th xcution bhavior of a program may chang du to, for xampl, th load in th ytm, FS nd to b abl to adjut to chang. Howvr, adjuting FS to th latt chang i dangrou whn th corrponding proc run abnormally. Thrfor, th proc controllr adjut ach CU tim of FS ( T ) lightly by multiplying th diffrnc btwn th CU tim that a corrponding proc actually

6 pnd bfor it voluntarily rlinquih th CU and T with a contant (calld an incra or a dcra caling factor) a hown in th following. If T = ( Cc C ), thn th adjutmnt i not ndd. (3) If T < ( Cc C ), thn T hould b incrad by uing th following rul: {( C C ) T } ( x 00) T = T + c, (4) whr x i an incra caling factor (%). If T > ( Cc C ), thn T hould b rducd by uing th following rul: { T ( C C )} ( y 00) T = T c, (5) whr y i a dcra caling factor (%). According to thi, throughout th xcution, whnvr a proc voluntarily rlinquih th CU (.g., whn th proc block itlf pnding th compltion of th I/O opration in th wait tat), if T i mallr or gratr than th CU tim that th proc actually pnd bfor it voluntarily rlinquih th CU, thn it i incrad or dcrad lightly by uing an incra or a dcra caling factor. 4. Implmntation Thi ction dcrib th implmntation of th loggr and th proc controllr in dtail. 4. Th Loggr Th main work of th loggr i to crat a log and a FS. A log (hown in Figur 3) i implmntd a an array of tructur containing information about tim (clock), proc idntifir (pid) and proc tat (p_tat). A FS (hown in Figur 3) i implmntd a an array of tructur containing information about proc tat (p_tat) and tim pnt ( T ). In ordr to idntify th FS of ach program, th program nam i attachd to th top of th array. Figur 3 how how to u th log to crat a FS and it i dcribd in dtail blow.

7 log clock pid p_tat tart poition FS program nam clock n pid p_tat n p_tat tim pnt ( Tp) nd poition currnt poition pid program nam Figur 3: Th diagram of how to u th log to crat a FS. How to crat a log: whn a program i xcutd, if it FS do not xit thn th information ncary to crat th FS i rcordd in th log at vry dipatch until th corrponding proc trminat. That i, whn th corrponding proc i th currnt running proc, th information about tim, proc idntifir and proc tat from now (i.., rady or wait tat) i ntrd into th log via a pointr giving th currnt poition. Thn, th pointr i incrmntd to th nxt log ntry and th nxt waiting proc i dipatchd. whn th corrponding proc i th nxt waiting proc, th information about tim, proc idntifir and proc tat from now (i.., run tat) i ntrd in th log via a pointr giving th currnt poition. Thn, thi pointr i incrmntd to th nxt log ntry and th corrponding proc i dipatchd. Not that th addr of th log ntry whn th proc tart xcution and whn it finih xcution ar rpctivly rfrrd to a th tart and th nd poition. And th data btwn th two poition ar ud for crating th FS of th program. How to crat a FS: at th nd of th xcution, pac for th FS of th program i allocatd and th data for ach FS ntry i thn cratd from th log btwn th tart and th nd poition. Whn thr i mor than on proc in th ytm, it i ncary to dtrmin which proc() corrpond to which program. By uing thi information, th data for th proc() which corrpond to th program nam i takn from th log. Not that for our chdulr only th tim pnt in run tat and in wait tat hav uful information, inc th tim pnt in rady tat dpnd on th numbr of th proc waiting for th CU to bcom availabl in th rady quu and ha no baring on futur xcution bhavior. Thrfor, w conidr th ri of log ntri in which thir p_tat lmnt rcording th concutiv witching

8 btwn run tat and rady tat, a on FS ntry who p_tat lmnt i run tat and T lmnt i th ummation of th tim pnt in run tat in that ri, and it i calculatd uing th following quation whr C i i a clock i lmnt in th log ntri in that ri. T { C rady) C ( run) } + + { C ( rady) C ( run) } + { C ( wait) C ( )} p = 2 ( L n n n+ 2 n+ run 4.2 Th roc Controllr Th main work of th proc controllr i to mak a chduling dciion bad on FS and to adjut an xiting FS to chang. Thi can b implmntd by dividing into four pha: ) whn a proc i cratd, 2) whn a proc u up it tim-lic, 3) whn a proc block itlf, and 4) whn a proc trminat. Th following i dcribing ach pha in mor dtail. Th diagram of how to chdul bad on FS and th procing flowchart ar hown in Figur 4 and 5 rpctivly. chduling tabl pid pid 2 currnt information tabl tart tim ( C) xpctd tim ( T ) FS program nam p_tat tim pnt ( Tp ) Figur 4: Th diagram of how to chdul a proc bad on FS. ) Whn a proc i cratd, if th FS of th program it run xit, thn (a) it proc idntifir i tord in a tabl calld chduling tabl and pac for a tabl calld currnt information tabl i allocatd. A chduling tabl (hown in Figur 4) i an array of tructur containing proc idntifir (pid) of th proc that will b chduld bad on FS and a pointr to it currnt information tabl. A currnt information tabl (hown in Figur 4) i a tructur containing th tim a proc tart uing th CU for ach allocatd portion of CU ( C ), th xpctd CU tim a proc would u from C until it voluntarily rlinquih th CU ( T ) and a pointr to th FS ntry (pf_ptr). (b) Nxt, ach lmnt of th currnt information tabl i initializd a blow. C 0,

9 pf_ptr th addr of th firt FS ntry who p_tat i run tat, T T which i accd via pf_ptr. 2) Whn a proc u up it tim-lic, (a) th lmnt of th currnt information tabl, T and T T ( C C ) c, C C if T Tm, or C 0 if T > Tm, c whr T m i th maximum dipatch dlay tim. (b) Nxt, th proc i chduld according to () and (2). That i, C, ar updatd a blow. if T Tm, thn th proc i allowd to continu uing th CU. if T > Tm, thn th nxt waiting proc i dipatchd. 3) Whn a proc block itlf, Not that th nxt waiting proc i alo dipatchd if T < 0. (a) th lmnt of FS ntry, T, i adjutd according to (3) through (5). That i, if ( C C ) = 0 T c, thn T if ( C C ) < 0 c T (no adjutmnt). T, thn T T T ( C C ) if ( C C ) > 0 c { } ( x 00) c T, thn T T T ( C C ) { } ( y 00) c (b) Each lmnt of th currnt information tabl i updatd a blow. C 0, pf_ptr th addr of th nxt FS ntry who p_tat i run tat, T T which i accd via pf_ptr. 4) Whn a proc trminat, (a) th lmnt of FS ntry, T, i adjutd according to (3) through (5). That i, if ( C C ) = 0 T c, thn T if ( C C ) < 0 c T (no adjutmnt). T, thn T T T ( C C ) { } ( x 00) c

10 T, thn T T T ( C C ) if ( C C ) > 0 c { } ( y 00) c (b) Th currnt information tabl i fr and it aociatd chduling tabl ntry i rmovd. Not that whn a proc chang from rady tat to run tat, if C = 0 thn C Cc. a proc i cratd (a) proc idntifr i tord in chduling tabl (b) th currnt information tabl i allocatd and initializd C 0 pf_ptr th addr of th firt FS ntry T Tp rady tat wait tat th currnt information tabl i updatd if C = 0, thn C Cc (a) th currnt information tabl i updatd T T ( Cc C ) C Cc if T < Tm, or C 0 if T > Tm (b) th proc i chduld a blow if T < Tm, thn it i allowd to continu uing th CU if T > Tm, thn th nxt waiting proc i dipatchd (a) th lmnt of FS ntry, Tp, i updatd according to T ( Cc C ) (b) th currnt information tabl i updatd C 0 pf_ptr th addr of th nxt FS ntry T Tp timlic run tat (a) th lmnt of FS ntry, Tp, i updatd according to T ( Cc C ) (b) th currnt information tabl i fr, and th chduling tabl ntry i rmovd a proc trminat Figur 5: Th procing flowchart. 5. Exprimntal Evaluation In thi ction, w prnt vral xprimnt dignd to valuat th ffctivn of our chdulr, which i implmntd a a modification to th BSD/OS 2. krnl.

11 W prformd two t of xprimnt: ) xprimnt with a tt program, and 2) xprimnt with xiting program. W cho gzip, mrg, and ort a th xampl of th xiting program. Gzip i uful for backing-up or tranfrring larg fil whil mrg and ort ar ud a lot in databa ytm. Th following i dcribing ach program in dtail. A tt program i a program that loop 20 tim through work A and work B. Work A incrmnt an intgr variabl by on for th amount of tim pcifid by th argumnt nt to th program. Work B go to lp in th wait tat for a fixd tim of cond. W will rfr to th proc of th tt program a th tt proc. Gzip i a fat and fficint fil comprion program ditributd by th GNU projct. Th baic function of gzip i to tak a fil, compr it, av th comprd vrion a filnam.gz, and rmov th original, uncomprd fil. Whn compring fil, on of th option, 2, L, 9 can b ud to pcify th pd and quality of th comprion ud. pcifi th fatt mthod, which compr th fil l compactly, whil 9 u th lowt but bt comprion mthod. In our xprimnt, w ran gzip a gzip 2 fil ; fil contain 200,000 numbr of intgr which ar gnratd by th library function calld rand(). Mrg i a uful program for combining all chang or diffrnc into on fil. In our xprimnt, w ran mrg a mrg outputfil fil2 fil3, rulting all diffrnc that lad from fil2 to fil3 into outputfil ar incorporatd. Fil2 and fil3 contain 00,000 numbr of intgr which ar gnratd by rand(). Sort i a txt fil orting program. It ort txt fil by lin and output th rult in th tandard output or in th fil pcifid by option -o. In our xprimnt, w ran ort a ort fil2 fil3 -o outputfil ; fil2 and fil3 ha th am contnt a mntiond abov. Th purpo of th firt t of xprimnt i to xplor th cot involvd in our chdulr, and to vrify that our chdulr work a xpctd, i.., it dlay proc witching a xpctd, and it adjut an xiting FS to chang a xpctd. Th purpo of th cond t of xprimnt i to xamin th prformanc of th xiting program whn thir corrponding proc ar chduld uing our chdulr. Mor pcifically, w xamind th procing tim of ach xiting program with rgard to th lngth of th maximum dipatch dlay tim, and th ffct on th procing tim of adjuting th xiting FS to chang whn ach program i xcutd a numbr of tim. All our xprimnt wr run on a 20 MHz ntium with 32 MB of mmory, running our modifid vrion of BSD/OS 2.. In addition, th xprimnt wr conductd in ingl ur mod with th prmption nabld, and timlot and tim-lic ar and 00 millicond rpctivly.

12 5. Tt rogram Thi ction prnt th xprimntal rult with th tt program for th cot involvd in our chdulr and th validation of our chdulr. 5.. Ovrhad Th cot involvd in crating and toring FS on mmory and th cot involvd in chduling bad on FS, whn running th tt program, ar a follow. W did not notic a diffrnc btwn th procing tim whn a FS wa cratd for th tt proc and whn it wa not. Thrfor, th ovrhad of logging th information of th tt proc and crating FS i rlativly mall. Whn th maximum dipatch dlay tim i zro, th procing tim whn th tt proc i chduld by our chdulr i th am a whn it i chduld by a convntional tim-haring chdulr. Thrfor, th ovrhad of chduling bad on FS i mall. According to th abov xprimntal rult, th ovrhad of our chdulr i mall Dlay roc Switching In ordr to vrify that our chdulr can dlay proc witching a xpctd, w maurd th procing tim of th tt program whn th lngth of th maximum dipatch dlay tim wa varid a 0, 0, 40, and 70. In thi xprimnt, th argumnt of th tt program wa givn a 75, 25, 50 and 200 millicond. In ordr to nabl proc witching whn a givn tim-lic xpir, th tt program coxitd with a CU intniv program calld loop program, throughout th xprimnt. Loop program i a program that incrmnt an intgr variabl by on in an infinit loop. W will rfr to th proc of th loop program a th loop proc. Figur 6 how th xprimntal rult plottd with th procing tim on y-axi normalizd by th procing tim whn uing a convntional tim-haring chdulr. Thi figur how that whn th rquird CU tim i mor than th tim-lic (00 millicond) and it diffrnc i mallr than th maximum dipatch dlay tim, thn th procing tim whn uing our chdulr bcom hortr. For xampl, whn th rquird CU tim i 25 millicond and th maximum dipatch dlay tim i 40 millicond, and whn th rquird CU tim i 25 and 50 millicond and th maximum dipatch dlay tim i 70 millicond. According to th rult, our chdulr dlay proc witching a xpctd.

13 rocing tim (normalizd) cpu75mc cpu25mc cpu50mc cpu200mc Maximum dipatch dlay tim Figur 6: Th rlation btwn th maximum dipatch dlay tim and th procing tim of th tt program whn th argumnt to th tt program i givn a 75, 25, 50, and 200 millicond Adjuting An Exiting FS In ordr to vrify that our chdulr can adapt an xiting FS to chang a xpctd, w xcutd th tt program with it initial FS diffrnt from it actual xcution bhavior for 20 tim and maurd th procing tim for ach xcution. During th xprimnt, th tt program coxitd with th loop program, in ordr to nabl proc witching whn a givn tim-lic xpir. Figur 7 how th rlation btwn th numbr of xcution and th procing tim, whn th maximum dipatch dlay tim i 20 millicond whil th incra (x) and th dcra (y) caling factor ar both varid from 0%, 20% and 30%. Figur 7(a) and (b) how th xprimntal rult whn w ran th tt program with it argumnt givn a 30 and 0 millicond rpctivly. Th initial FS wa cratd whn w ran th tt program with it argumnt givn a 20 millicond. Alo, th procing tim in Figur 7 i normalizd to th procing tim whn th initial FS of th tt program i th am a th actual xcution bhavior. Not that during ach xcution of th tt program, CU tim of th FS i adjutd whn th tt proc go to lp cond in th wait tat. During th firt xcution, whn th tt proc with it argumnt pcifying th amount of tim for work A a 30 millicond i running at th nd of it cond tim-lic, th CU tim it actually nd bfor going to lp cond bcom 0 millicond, which i mor than th maximum dipatch dlay tim (20 millicond). On th othr hand, th xpctd CU tim bad on th initial FS (0 millicond) i l than th maximum dipatch dlay tim (20 millicond). Thrfor, th initial FS i adjutd by uing (4). That i ach CU tim of th initial FS i incrad by uing th incra caling factor. And a th numbr of xcution bcom biggr, it finally bcom clo to 30 millicond. Th xprimntal rult hown in Figur 7(a) ar dicud in mor dtail.

14 rocing tim (normalizd) (a) cpu = 30 mc x=y= x=y= x=y= Numbr of xcution rocing tim (normalizd) (b) cpu = 0 mc x=y=0 x=y= x=y= Numbr of xcution Figur 7: Th ffct of adjuting th FS of th tt program to chang on it procing tim. tim-lic loop proc tt proc tim-lic loop proc tt proc tim-lic loop proc tt proc 00 m 50 m (a) 0 m dlay 000 m 00 m 00 m dlay (b) 000 m 0 m 50 m (c) 00 m 000 m 0 m 60 m Figur 8: Th xcution bhavior of a tt proc for work A of ach loop whn (a) th initial FS i th am a th actual xcution bhavior, (b) th numbr of tim th program i xcutd i mall, and (c) th CU tim of th initial FS i adjutd and bcom mor than 220 millicond. Whn th numbr of tim th program i xcutd i mall, for xampl, at th nd of th cond tim-lic of th firt xcution of th tt proc, th xpctd CU tim bad on FS for work A of ach loop i 0 millicond, which i l than th maximum dipatch dlay tim (20 millicond). A a rult, th tt proc i allowd to continu uing th CU intad of dipatching it to th loop proc. Aftr uing up 00 millicond mor of th CU tim, th xpctd CU tim bad on FS bcom l than

15 zro cauing th CU to b dipatchd to th loop proc (rcall th rul (in Sction 4.2) that th nxt waiting proc i dipatchd if T < 0 ). According to thi, th procing tim of th tt proc whn th initial FS i th am a th actual xcution bhavior and whn it i diffrnt ar th am a hown in Figur 8(a) and (b). Thrfor, th procing tim at th firt xcution in Figur 7(a) i on. A th numbr of tim th program i xcutd incra, ach CU tim of th initial FS i adjutd and bcom mor than 220 millicond. Thrfor, whn th tt proc i running at th nd of it cond tim-lic, th xpctd CU tim bad on FS for ach loop i mor than 20 millicond, which i mor than th maximum dipatch dlay tim (20 millicond). A a rult, th CU i dipatchd to th loop proc. Morovr, at th nd of it third tim-lic, th xpctd CU tim bad on FS bcom l than zro cauing th CU to b dipatchd to th loop proc a hown in Figur 8(c), whil th tt proc with th initial FS th am a th actual xcution bhavior i allowd to continu uing th CU for 0 mor millicond a hown in Figur 8(a). According to thi, th procing tim of th tt proc whn th initial FS i diffrnt from th actual xcution bhavior bcom biggr. Thrfor, th procing tim in thi ca i mor than on a hown in Figur 7(a). In addition, Figur 7(a) how that th biggr th incra caling factor i, th fatr ach CU tim of FS bcom mor than 220 millicond. For xampl, whn th numbr of xcution i two, th procing tim with th incra caling factor of 20% and 30% ar mor than on, whil th on with th incra caling factor of 0% i till about on. A th numbr of tim th program i xcutd incra mor, ach CU tim of th initial FS i adjutd and bcom clo to 30 millicond. Thrfor, whn th tt proc i running at th nd of it third tim-lic, th xpctd CU tim bad on FS for ach loop i l than 20 millicond, which i alo l than th maximum dipatch dlay tim (20 millicond). A a rult, th tt proc i allowd to continu uing th CU intad of dipatching it to th loop proc. According to thi, th procing tim of th tt proc whn th initial FS i th am a th actual xcution bhavior and whn it i diffrnt bcom th am. Thrfor, th procing tim in thi ca bcom on again a hown in Figur 7(a). In addition, Figur 7(a) how that th biggr th incra caling factor i, th fatr ach CU tim of FS bcom clo to 30 millicond. For xampl, whn th numbr of xcution i mor than 3, th procing tim with th incra caling factor of 20% and 30% bcom on again, whil th on with th incra caling factor of 0% i till mor than on. In th am way, th xprimntal rult hown in Figur 7(b) can b xplaind. In brif, during th firt xcution, whn th tt proc with it argumnt pcifying th amount of tim for work A a 0 millicond i running at th nd of it firt tim-lic, th CU tim it actually nd bfor going to lp cond bcom 0 millicond whil th xpctd CU tim bad on th initial FS i 0 millicond (which i biggr). Thrfor, th initial FS i adjutd by uing (5). That i ach CU tim of

16 th initial FS i dcrad by uing th dcra caling factor. And a th numbr of xcution bcom biggr, it finally bcom clo to 0 millicond. 5.2 Exiting rogram Thi ction how th ffct of th maximum dipatch dlay tim and th ffct of adjuting th FS of ach xiting program (gzip, mrg, and ort), on it procing tim Th Lngth of Th Maximum Dipatch Dlay Tim v. rocing Tim W ran th thr xiting program on at a tim and found th rlation btwn th lngth of th maximum dipatch dlay tim and th procing tim of th proc of ach program. In ordr to nabl proc witching whn a givn tim-lic xpir, throughout th xprimnt, th xiting program coxitd with th loop program. Figur 9 how th xprimntal rult plottd with th procing tim on y-axi normalizd by th procing tim whn uing a convntional timharing chdulr (TSS). For rfrnc, w alo how th tim ud to crat FS in Figur 9. Alo, tabl how, according to FS, th numbr of tim th CU and th I/O rourc ar obtaind by ach program including tim ud. Not that th numbr of tim th I/O rourc i obtaind i hown in parnthi. Alo, th total tim ud to xcut gzip, mrg and ort program ar 5, 05 and 9 cond rpctivly. Th xprimntal rult hown in Figur 9 ar dicud in mor dtail. rocing tim (normalizd) (a) gzip rocing tim (normalizd) (b) mrg rocing tim (normalizd) (c) ort 0.8 TSS crat FS Tm=0 Tm=20 Tm=40 Tm=60 Maximum dipatch dlay tim Tm= TSS crat FS Tm=0 Tm=20 Tm=40 Tm=60 Maximum dipatch dlay tim Tm= TSS crat FS Tm=0 Tm=20 Tm=40 Tm=60 Maximum dipatch dlay tim Tm=80 Figur 9: Th ffct of th maximum dipatch dlay tim on th procing tim (gzip, mrg, and ort).

17 Tabl : Th rourc uag of gzip, mrg and ort program bad on FS. tim ud numbr of tim CU (I/O) rourc wr obtaind (millicond) gzip mrg ort undr 0 (02) 5 (0) 54 (05) 0 to undr 20 5 (05) 0 (0) 43 (26) 20 to undr 30 0 (07) 0 () 2 (33) 30 to undr 40 0 (5) () 9 (33) 40 to undr 50 0 () 0 (0) 7 (23) 50 to undr 60 0 (07) 0 (0) (6) 60 to undr 70 (04) 0 (0) 3 (02) 70 to undr 80 (0) 0 (0) 0 (00) 80 to undr 90 0 (00) 0 (0) 0 (04) 90 to undr 00 0 (00) 0 () (04) ovr (0) (4) 6 (0) total 53 (53) total 7 (7) total 56 (56) In th ca of gzip: tabl how that th total numbr of dipatch and th total numbr of tim th CU rourc i obtaind by gzip ar 06 and 53 rpctivly. Out of th total numbr of tim th CU rourc i obtaind, about 50% (25 tim) of th tim it ud mor CU tim than th tim-lic (00 millicond). Whn th rquird CU tim i mor than th tim-lic (00 millicond), by uing our chdulr, th procing tim bcom mallr a th lngth of th maximum dipatch dlay tim i incrad. For xampl, th procing tim whn th maximum dipatch dlay tim i 20 and 60 millicond, i improvd 4.2% and 7.8% rpctivly. Thrfor, our chdulr mak a noticabl improvmnt in thi ca. In th ca of mrg: tabl how that th total numbr of dipatch and th total numbr of tim th CU rourc i obtaind by mrg ar 4 and 7 rpctivly. Out of th total numbr of tim th CU rourc i obtaind, only on tim did it u mor CU tim than th tim-lic (00 millicond). And that tim it ud th CU rourc only 3 millicond longr than it normal tim-lic. A a rult, th procing tim whn uing our chduling i almot th am a whn not uing it, rgardl of how much th lngth of th maximum dipatch dlay tim i incrad. For xampl, th procing tim whn th maximum dipatch dlay tim i 60 millicond i improvd only 0.5%. Thrfor, th ffct of our chdulr i rlativly mall in thi ca. In th ca of ort: tabl how that th total numbr of dipatch and th total numbr of tim th CU rourc i obtaind by ort ar 32 and 56 rpctivly. Out of th total numbr of tim th CU rourc i obtaind, only 0% (6 tim) of th tim it ud CU tim mor than th tim-lic (00 millicond). Howvr, th procing tim bcom mallr a th lngth of th maximum dipatch dlay

18 tim i incrad. For xampl, th procing tim whn th maximum dipatch dlay tim i 60 millicond i improvd 3.0%. In thi ca alo, our chdulr mak a noticabl improvmnt Adjuting An Exiting FS v. rocing Tim W varid th numbr of xcution of ach program from to 0 and obrvd th ffct on th procing tim of adjuting th xiting FS. During th xprimnt, th xiting program coxitd with th loop program, in ordr to nabl proc witching whn a givn tim-lic xpir. Figur 0 how th rlation btwn th numbr of xcution and procing tim, whn th maximum dipatch dlay tim i 20 millicond whil th incra (x) and th dcra (y) caling factor ar both varid from 0%, 20% and 30%. For comparion, w alo how th rult whn th maximum dipatch dlay tim and th incra and th dcra caling factor ar zro. In addition, th procing tim in Figur 0 i normalizd to th procing tim of th firt xcution. Not that during ach xcution of th xiting program, CU tim of th FS i adjutd whn th proc of th xiting program ar blockd for an I/O opration to b compltd in th wait tat. In Figur 0, thr i a trnd that th procing tim of th proc of gzip program will dcra a th numbr of xcution bcom largr, whil w did not notic thi kind of trnd for th mrg and th ort program. Thi how that adjuting th FS of th thr xiting program ha vry littl or no ffct on th procing tim. rocing tim (normalizd) (a) gzip x=y=0,tm= x=y=0,tm=20 x=y=20,tm= x=y=30,tm= Numbr of xcution rocing tim (normalizd) (b) mrg x=y=0,tm=0 x=y=0,tm=20 x=y=20,tm=20 x=y=30,tm= Numbr of xcution rocing tim (normalizd) (c) ort x=y=0,tm=0 x=y=0,tm=20 x=y=20,tm=20 x=y=30,tm= Numbr of xcution Figur 0: Th ffct of adjuting th xiting FS to chang on th procing tim (gzip, mrg, and ort). 6. Concluion Thi papr propod a proc chdulr that control th haring of th CU rourc bad on bhavior of a proc. Th pcial fatur of our chdulr i that () whn a program i xcutd for th firt tim, it

19 log th bhavior of th corrponding proc at vry dipatch and thn crat an advancd knowldg calld FS (rogram Flow Squnc) at th nd of th xcution, and (2) whn th program i xcutd from thn on, it chdul th corrponding proc bad on th FS, i.., it dlay proc witching in ordr to allow th corrponding proc to continu it xcution, whn it i prdictd from FS that th corrponding proc nd a littl bit mor CU tim bfor it voluntarily rlinquih th CU. It alo adjut FS to chang bad on th fdback obtaind from ach xcution. Alo, our xprimntal rult how that procing tim can b rducd by uing our chdulr. Howvr, th pric to b paid for rducing th procing tim i that w rduc th fairn of th ytm. Evn though thi work i motivatd by th qution why can't oftn-ud program run fatr, w nd to nur that th rulting unfairn do not outwigh th prformanc gain obtaind. Thi could b don by uing th arly proc witching mchanim to compnat for th dlay proc witching during othr tim. Alo, th impact of varying th maximum dipatch dlay tim on fairn nd to b xplord. Bid tho ara mntiond abov, om of our futur work will alo includ valuating th ffctivn of our chdulr with othr program, xploring th cot of toring FS on th dik, dvloping a mthod to dtrmin which proc running bhalf of oftn ud program, and xtnding our chdulr to dal with program coniting of multipl proc. Acknowldgmnt W would lik to thank Jam Michal rry for hi aitanc in proofrading thi papr. Rfrnc [] H. Chu and K. Nahrtdt, A oft ral tim chduling rvr in UNIX oprating ytm, Tchnical Rport UIUCDCS-R , Dpartmnt of Computr Scinc, Univrity of Illinoi at Urbana Champaign, March 997. [2] Silbrchatz and. Galvin, Oprating Sytm Concpt (5th d.), John Wily & Son, 997. [3] C. Mrcr, S. Savag, and H. Tokuda, rocor capacity rrv for multimdia oprating ytm, Tchnical Rport CMU-CS-93-57, School of Computr Scinc, Carngi Mllon Univrity, May 993. [4] C. Waldpurgr and W. Wihl, Lottry chduling: flxibl chduling proportional-har rourc managmnt, In roc. of th t USENIX Sympoium on Oprating Sytm Dign and Implmntation, pp.-, Nov [5] C. Waldpurgr and W. Wihl, Strid chduling: dtrminitic proportional-har rourc

20 managmnt, Tchnical Rport MIT/LCS/TM-528, MIT laboratory for computr cinc, Jun 995. [6] M. Jon, D. Rou, and M. Rou, CU rrvation and tim contraint: fficint, prdictabl chduling of indpndnt activiti, In roc. of th 6th ACM Sympoium on Oprating Sytm rincipl, pp.98-2, Oct [7] D. Golub, Oprating ytm upport for coxitnc of ral-tim and convntional chduling, Tchnical Rport CMU-CS-94-22, School of Computr Scinc, Carngi Mllon Univrity, Nov [8] B. Ford and S. Suarla, CU inhritanc chduling, In roc. of th 2nd USENIX Sympoium on Oprating Sytm Dign and Implmntation, pp.9-06, Oct [9]. Goyal, X. Guo, and H. Vin, A hirarchical CU chdulr for multimdia oprating ytm, In roc. of th 2nd USENIX Sympoium on Oprating Sytm Dign and Implmntation, pp.07-2, Oct [0] Y. Kwok and I. Ahmad, Dynamic critical-path chduling: an ffctiv tchniqu for allocating tak graph to multiprocor, IEEE Tran. aralll and Dit. Sytm, vol.7, no.5, pp , May 996. [] H. Wang, A. Nicolau, and K. Siu, Th trict tim lowr bound and optimal chdul for paralll prfix with rourc contraint, IEEE Tran. Comput., vol.45, no., pp , Nov [2] M. Wu and W. Shu, On paralllization of tatic chduling algorithm, IEEE Tran. Softwar Eng., vol.23, no.8, pp , Aug [3] [4] 2a.ap