Anale. Seria Informatică. Vol. XI fasc Annals. Computer Science Series. 11 th Tome 2 nd Fasc. 2013

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1 Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc EFFECTS OF SYSTEM PAGIG / THRASHIG OVERHEA O SYSTEM PERFORMACE BASE O EGREE OF MULTIPROGRAMMIG Ahigbe Mudu Thusday Ehis eatment of Comute Science, Fedeal Univesity of Agicultue Abeouta, igeia ABSTRACT: Thee is usually a stong concen about the functionality of comute systems and vey little concen about its efomance. In geneal, efomance becomes an issue only when the efomance becomes eceived as being oo by uses. Majo constaints on systems show themselves in fom of extenal symtoms, stess conditions and ing being the chief foms. Thashing occus when a comute s vitual memoy subsystem is in a constant state of ing, aidly exchanging data in memoy fo data on dis, to the exclusion of most alication ocessing. This causes the efomance of the system to degade by multile odes of magnitude. We develoed analytical models with comutational algoithms that ovide the values of desied efomance measues. Lyaonuv stability citeia ovide sufficient conditions fo the system validity, the esult shows that the savings geneated fom the e- based, offsets the additional time needed to ocess the incease numbe of e- faults. KEYWORS: Paging, Thashing, Multiogamming, Intefault, Fames and ovehead. ITROUCTIO Paging fom the layman oint of view is a technique used by vitual memoy oeating system to hel ensue that the data you need is available as quicly as ossible. When a ogam needs a e that is not in the main memoy, the oeating system coies the equied e into memoy and coies anothe e bac to the dis. As this ocess continues, a e fault occus when the addess of the e being equested is invalid and in that case, the alication is usually aboted. It is the e in ate that is of imay concen, because e in activity occus synchonously [MA94]. A e in incus a time cost fo the hysical I/O and a moe significant incease in ocesso usage. Page in activity slows wn the ate at which tansactions flow though the system, that is, tansactions tae longe to get though the system. If a system es not have enough es, thashing is a high ing activity, and the e fault ate is high. This leads to CPU utilization. In moden comutes, thashing may occu in the ing system (if thee is not sufficient hysical memoy o the dis access time is ovely long), o in the communications system (esecially in conflicts ove intenal bus access), etc. eending on the configuation and algoithms involved, the thoughut and latency of a system may degade by multile odes of magnitude as a esult of excessive ing [MA8]. In vitual memoy system, thashing may be caused by ogams o wo load that esent insufficient locality of efeence, if the woing set of a ogam o a woload cannot be efficiently held within hysical memoy, then constant data swaing, i.e. thashing may occu. Hence, the efomance evaluation of comute system and netwos has thus become a emanent concen of all who use them... Identifying System Constaints Majo constaints on system show themselves in the fom of extenal symtoms, stess conditions and ing being the chief foms. The fundamental thing that has to be undestood is that actically evey symtoms of oo efomance aises in a system that is congested. Fo examle, if thee is a slowwn in a system, tansactions ing data set activity ile u; thee ae waits on stings; thee ae moe tansactions in the system, thee is theefoe a geate vitual stoage demands, thee is ing, and because thee ae moe tansactions in the system, the tas disatche uses moe ocesso owe scanning the tas chains. We then have tas constaints; tansaction class limit is exceeded and adds to the ocesso ovehead because of eties and so on. The esult of this is that the system shows heavy use of its esouces and this is the tyical system stess. Thashing occus when a comute s vitual memoy subsystem is in a constant state of ing, aidly exchanging data in memoy fo data on dis, to the exclusion of most alication level ocessing. This causes the efomance of the system to degade o collase. Hence, the battle cy fo system otimal efomance esonates with a gowing and wide sead concen to imove the efomance of comute systems and to fail to so today will amount to inviting catastohic system failue tomoow... Memoy Queuing Multiogamming is a cental at of moden oeating systems. It allows fo seveal ogams (jobs), tansactions, ocesses and equests to be memoy esident at the same time, shaing the system esouces, such as ocessos and I/O devices. Most

2 46 ogams not ovela thei I/O and ocessing activities, so that while one ogam is maing use of the ocess othes ae undegoing I/O ocessing. Theefoe, multiogamming leads to a bette use of the system esouces, by eeing I/O devices unning concuently with ocessos. Howeve, due to the finitude of eal memoy, the numbe of ogams in execution may affect system efomance. Fo examle, in vitual memoy systems, as the multiogamming level inceases, the ing and swaing activities also incease and may cause a eduction of thoughut of oductive wo. Thus, thee must be contol of the maximum numbe of ogams allowed to shae memoy at the same time. Usually, oeating systems contol the oveall load by acting on the degee of multiogamming..3. Poblem escitions Paging moves individual es of ocessing fom main memoy to dis and bac, as a esult geneates I/O taffic. Each time a e is needed that is not cuently in memoy, a e fault occus. An invalid e fault occus when the addess of the e being equested is invalid; in this case, the alication is usually aboted and deending on the configuation and algoithms involved, the thoughut and latency of a system may degade by multile odes of Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 magnitude. The intensity of ing activities is measued by e ins (es moved fom dis to memoy), and e outs (es moved fom memoy to dis), as exhibited in figue. Page ins incus a time cost fo hysical I/O and a moe significant incease in ocesso usage, since it has to wait until the e tansfe comletes. As a esult, most esent day oeating systems use demands ing, which means that a e of code o data is not ead into memoy until the e is needed. In an ove committed situation, whee the numbe of es actively in use exceeds the numbe of es of hysical memoy, it becomes necessay to select es that will be emoved fom hysical memoy in ode to mae oom fo new es. When the ing activity stats to incease, the load on the ing device inceases and it eventually becomes the bottlenec. The thoughut deceases and eventually goes to zeo (Thashing) and as such, ing activity should be included in efomance model systems. The est of this ae is stuctued in the following manne: - section () discusses the liteatue eview, section (3) focuses on the methology of the w while section (4) analyzes the ing activities, imlemented the method discussed in the body of the ae and evaluated the esult using Lyaunov stability citeia. Section (5) discusses the summay and conclusion of the ae. Physical memoy is dive Vitual memoy Addess saces Figue : System Paging Activities. LITERATURE REVIEW Poo efomance of the oeating systems can have consideable imact on alication efomance. To avoid the oeating system fom limiting alication efomance, it must be highly cuent. In the ealy 990 s, eseaches identified memoy efomance as citical to system efomance. [KGP89] noted that Cache efomance and Coheency ae citical asects of hadwae which must be taen into account. They exlicitly advocated that oeating systems must be otimized to meet the demands of uses fo high efomance. They ointed out that OS ae lage and comlex and the otimization tas is difficult and without cae, tuning can esult in inceased comlexity with little imact to the end use s efomance. The dawbac hee was the ey to focus otimization by identifying efomance oblems. [WW00] imlementation and analysis of e based comession in the OS/ oeating system yielded two esults with esect to memoy. Fist, OS with e based comession uses less vitual memoy than an oeating system without e based comession. In an unconstained envionment, the system with e based comession will geneate fewe e faults than the system without e based comession, which tanslates into faste efomance. Secondly, a system with e- based comession equies moe loced (wied) memoy than a system without e based,

3 which effectively educes the amount of memoy available to the est of the system. This will oduce no notable effect in an unconstained envionment; howeve, a small eduction in the amount of memoy will cause an incease in the numbe of e faults. Also we found that the time saved due to comession offsets the additional time caused by the incease in numbe of e faults. Though e based comession imoves the efomance of a demand ing oeating system, it educes the amount of memoy available to the est of the system which es not suot ou effot. [B06] used the numbe of queies being executed concuently as a measue of multiogamming level, and choose to define multiogamming level as being the numbe of queies in any hase of execution. The dawbac hee is that data shaing is based on obsevation that in cetain data based alications, multile queies may be accessing the same elations concuently, and thee is a high obability that index es will be accessed by these alications. [AEP] oosed a tool fo lanning and contol, costing systems lay a consideable ole in oviding infomation needs fo manages. This eseach sees to exloe such oganizational factos as oganization size, industy tye, cost stuctue, the imotance of cost infomation and oducts and sevices. This study fails to incooate othe imotant vaiables which ae liely to influence cost system design... System thashing ovehead Ovehead denotes hadwae esouces use by the oeating system. It can be viewed as comosed of two ats:- a constant one and a vaiable one. The fome coesonds to those activities efomed by an OS that not deend on the level of system load, such as the CPU time handle an I/O inteuts. The vaiable comonent of ovehead stems fom activities that ae closely associated with the system load [ZQ93]. Fo examle, as the numbe of jobs in memoy inceases, the wo ne by memoy management modules also inceases (Thashing) [MA94]. Basically, thee ae two aoaches fo eesenting ovehead in efomance models. One aoach uses a secial class of the model fo eesenting the ovehead of the OS activities efomed on behalf of the alication ogams. Thee ae oblems associated with this aoach. Because of its vaiable comonent, the sevice demands of the secial class have to be made load deendent. Thus, wheneve the intensity aametes (e.g. multiogamming level and aival ate) of the alication classes change, the sevice demands of the ovehead class also have to be modified. The inte-deendency between ovehead aametes and Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 multiogamming mix may mae this aoach imactical [MLT]. 3. METHOOLOGY Most moden comute systems have ing diss that hold the es of the vitual addesses of the seveal ocesses. As a ocess e fault ate (numbe of e faults divided by the numbe of memoy efeences) inceases, a geate otion of the ocess execution time is sent on the ing device. The load on the ing device affects all ocesses in execution. We shall show how the ing activity can be taen into account when modeling comute system. 3.. Modeling Paging Activity Let be the index of the ing device but this device can also be used to stoe files othe than ocess addess saces, a ocess sevice demand at the ing device may be decomosed into two comonents: one due to and anothe not due to ing ing ( ) P ( ) which is a given aamete. = + () P P The oblem hee is how to estimate( ). We can say that aveage sevice demand at the ing device due to ing is equal to the aveage numbe of e faults multilied by the aveage dis time to sevice a e fault ( S ). Hence 47 = aveage. numbe. of. e. faultsχ S () Since the aveage sevice time e e fault can easily be comuted as a function of the dis hysical chaacteistics and the size of a vitual e, ou oblem educes to estimating the aveage numbe of e faults e ocess. Let f be the numbe of e fames allocated to a ocess in maim memoy. Let IFT f be a function that gives the inte fault time of a ocess when f e fames ae allocated to the ocess. The inte fault time is defined as the aveage time between consecutive e faults. S if we divide the total CPU time of a ocess ( cu ) by the value of the IFT ( f ) function, we obtain the aveage numbe of e faults. The gah of the IFT function is monotonically inceasing as shown in figue.

4 48 Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 IFT(f) o. of e fames Figue : Intefault Time vesus umbe of Page Fames Initially, the intefault time gows vey fast as the ocess acquies moe e fames. Howeve, as the numbe of e fames aoaches the size of the ocess woing set, the ate of incease of the intefault time deceases shaly and tends to zeo as the numbe of e fames allocated to the ocess aoaches its total numbe of es. At this oint, thee ae no e faults and the intefault time becomes equal to the total CPU time fo the ocess. A ossible exession fo such a function is: a a = [ + ] xs P / n F Theefoe, using Eq. (5) in Eq. (), we get that: P a a = + + xs P / n F (5) (6) IFT ( f ) cu = (3) + / / ( a f ) ( a F ) Whee F is the numbe of vitual es that comose a ocess addess sace and the constant a may be obtained fom measuement data. Let P be the total numbe of e fames to be divided by all ocesses and let n be the multiogamming level. Assuming that the e fames ae equally divided among all ocesses, each will be allocated a numbe of fames f given by P / n. Hence, the sevice demand due to ing can be witten as: cu = xs (4) ( / ) IFT P n ote that Eq. (6) is valid only when the degee of multiogamming is such that thee ae not enough e fames to stoe the comlete addess sace of all ocesses (i.e. when nxf > P). Othewise, thee ae no e faults and the ing device sevice demands due to ing activity ae zeo. We can now use Eq. (6) to adjust the esidence time ecuence exession fo the ing device in the algoithm given in figue (3). R' ( n ) = (7) P a a + + xs x + n ( n ) P / n F P Using Eq. (3) in Eq. (4), we get that:

5 3.. Thoughut Estimation We see that to comute the esidence time R ' i, ( ) we need the values of the obabilities Pi ( j / ). & To comute these obabilities we need the values of X, which deend on the the thoughuts esidence time values. We oose the following iteations aoach:. Estimate initial values fo the X. These estimates can be thoughuts obtained by aoximating the thoughut by its asymtotic ue bound, namely X min / i,, ( i, ). i= max i Although this is athe loose ue bound, it is usually good enough as a stating oint fo the iteation, P j /. Comute the obabilities i 3. Comute the esidence times, 4. Comute new values fo the thoughuts using Little s esult as X ( ) = R ' Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 i= 5. If the elative eo between the thoughuts obtained in the cuent iteation and the evious one is geate than a cetain toleance then goto ste (). Othewise, comute the final metics and sto. This aoach is secified in details in the fom of algoithms in figue (3) Algoithms Inut aametes:, S,,, R,, α j initialization : fo. : =. tor.., i fo. i: =. to.. if.. > 0. then m = / K i ev fo. : =. tor... Xo, = min / i,, ( i, ) i= max i Eo = + ; foce. enteing. loo. fo. fist. time Iteation loo { } while. eo >. begin comute. Queue. lenghts. fo. on L. devices fo. all. non L. device. i.. fo : =. to.. n I n n ( _ ) = + j i= comute. obabilies. fo. L. devices R Pi i X o j= i= j ev ( 0 / ) + + =,, ( ) ( / ) ( / ) P j = P o j = i i = j =..., comute.re sidence. Times fo. i : =. to.. fo. : =. to. R. Ri, '( ) = R X ev α + n I j comutethoughuts i i j= i ( ) ( ) j / α j P j / cuent fo. : =. to. R.. X = comute. queue. lenghts. e. class cu = ' i= cu ev cu X fo. all. non L. device. j.. fo. : =. tor. ni, X xr & comute. elative. eo X X Eo : = max Peae fo next iteation { while} R ' ( ) cu ( o ) fo. : =. to. R.. X : = X End; ev, Figue 3: Multile Class Algoithms 49

6 50 4. IMPLEMETATIO Examle: A comute system has one CPU and two diss :. and. dis :, dis. is used diss, ( fo ing uoses only. The sevice demands at the CPU and at dis ae 0.0 and 0.06 seconds esectively. The ing dis has an aveage sevice time equal to 30msecs. The system has 0Mbytes of memoy available fo ing. The size of the e fame is equal to 04 bytes. The addess sace of each ocess is equal to Mbytes. The constant a fo the intefault time function is assumed to be equal to Plot a gah of the thoughut vesus the multiogamming level. We need to comute the mode aametes fom the oblem data. The numbe of vitual es e addess sace F, is equal to x04 x04 /04 = 048. es. The total numbe of e fames is equal to P = 0x04 x04 /04 = 0,40. es P Also = 0 since the ing dis is used fo ing only and S = 0.03sec. We Can now use the Algoithms and comute the thoughut fo vaious values of the degee of multiogamming n. we need to use Eq. (7) fo the esidence time of the ing dis. Fo the othe Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 devices we use the nomal esidence time equation, In this examle, the esidence time equation becomes: R' ( n) = + n 0.03 ( ) 0,40 x x n n = ( n 3.8 ) x0.03 x + n ( n ) fon. > 5= 0,40/ 048 fon. 5 n=,..., R' = 0 ( n) The esulting thoughut gah is given in figue 4. It edicts the exected esult, namely that at the beginning, the thoughut inceases with the degee of multiogamming. Afte the ing activity stats to incease, the load on the ing device inceases and eventually becomes to the bottlenec. The thoughut deceases and eventually goes to zeo. This henomenon is called thashing. thoughut(job/sec) Multiogamming Figue 4: Thoughut vesus Multiogamming Level

7 4.. System Evaluation Fo a given system, stability is usually the most imotant thing to be detemined. Lyaonuv stability citeia is the most geneal method fo the detemination of stability of non- linea / o time vaying systems [B+06]. Lyaonuv esented two methods (fist and second methods) fo detemining the stability of dynamic systems descibed by odinay diffeential equations. The fist method consists of all ocedues in which the exlicit fom of the solutions of the diffeential equations is used fo the analysis. The second method es not equie the solutions of the diffeential equations. Theefoe, the second method is quite convenient fo the stability analysis of non linea systems, fo which the exact solution may not be obtained because solving non-linea / o time- vaying state equations is usually vey difficult. Lyaonuv ovides a sufficient condition fo asymtotic stability and this theoem is stated as follows; 4.. Theoem Suose that a system is descibed by x& = f ( x, t ) w h e e f ( t ) 0, = 0 f o. a l l. t If thee exist a scala function v( x, t ) having continuous, fist atial deivatives and satisfying the following conditions:. v( x, t ) is ositive definite,. v& ( x, t) is negative definite, Then the equilibium state at the oigin is unifomly asymtotically stable. We shall conside the second ode system descibed in the ae by: x& 0. x x =. x and we shall detemine the & stability of this state. Let us assume a tentative Lyaonuv function, v x = x Px whee. P. is. to. be.det e min ed. fom : A P + PA = o =.. 0. Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 By exanding this matix equation, we obtain thee simultaneous equations as follows: = = 0 = solving. fo.,,. we. obtain 3.. =.. To test the ositive definiteness of P, chec the deteminants of the successive incial minos. * Q = ( A P + PA) is ositive definite 3 Q = > 0 3 Clealy.. = > 0.. Clealy, P is ositive definite. Hence the equilibium state at the oigin is asymtotically stable in the lage and the Lyaonuv function is: v = x' x = ( 3x + xx + x ) v& = x + x ( ) If the e fault ate gets below the comuted ange, then the ocess losses a fame and if the e fault ate gets too high, the ocess gains a fame (see figue 5), and this esults in fewe e faults. Theefoe, ou aoach has been able to evaluate the effectiveness of the analytical model which is comosed of a set of fomulas and / o comutational algoithms. Inteestingly, we find that the savings geneated fom e- based offsets the additional time needed to ocess the incease numbe of e - faults. 5

8 5 Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 umbe of e faults o. of Fames Figue 5: Page Fault Fequency 5. COCLUSIO When a ogam needs a e that is not in the main memoy, the oeating system coies the equied e into memoy and coies anothe e bac to the dis and this is efeed to as ing. It is the e in ate that is of imay concen because a e in incus a time cost fo the hysical I/O and a moe significant incease in ocesso usage. eending on the configuation and algoithms involved, the thoughut and Latency of a system may degade by multile odes of magnitude. Hence, the battle cy esonates with a gowing and wide sead concen fo effective system efomance. In this ae, analytical model, comosed of a set of fomulas and comutational algoithms ovides the values of desied efomance measues as a function of the set of values of the efomance aametes. Lyaonuv stability citeia ovides a sufficient condition fo the system validity. Inteestingly, the esult shows that the savings geneated fom the e- based, offsets the additional time needed to ocess the incease numbe of e- faults even in a memoy constained envionment. Teminologies The tem woload designates all the ocessing equests submitted to a system by the use community duing any given eiod of time. Thoughut is the numbe of jobs that can be comleted e unit time. Residence time is the time sent by the job once it is loaded into memoy. The measue of load is given by the aveage numbe of batch jobs that ae concuently in execution and this numbe is called the aveage degee of multiogamming and is denoted by. otations K= numbe of devices R = numbe of classes of customes, = class.. oulation S = aveage sevice time of class customes at device i = aveage device demand of class - customes at device i; i, = Vi, S R = aveage esonse time e visit of class customes to device i, R ' i, = aveage esidence time of class customes at device i, n = aveage numbe of class customes at device i, X = class thoughut at device i, REFERECES [AEP] Taha Ahmadzadeh, Hossein Etemad Ahmed Pifeh - Exloation of Factos Influencing on Choice of the Activity Based Costing System in Ianain Oganization, Intenational Jounal of

9 [B06] [B+06] Anale. Seia Infomatică. Vol. XI fasc. 03 Annals. Comute Science Seies. th Tome nd Fasc. 03 Business Administation, Vol., o., 0. Haan Boal, avid J. ewitt - A Methology fo tatabase System Pefomance Evaluation, Comute Science eatment, Univesity of Wisconin Madison, 006. Qi B Pi-Chun Chen, Yang Yang, Qinqing Zhang - An Analysis of VOIP Sevices Using IXEV O evision of a system, IEEE Jounal on Selected Aeas in Communications, Vol. 4, o., es 36 45, 006. [MA94] aniel Menasce, Vigilo A.T. Almelda, Lay W. owdy - Caacity Planning and Pefomance Modeling, Pentice Hall, Inc. A Simon and Scheate Comany, Eaglewood Cliff, new Jesey 0763, es 64 0, 994. [MLT] 53 Heng gee M Yeow Leong Lee, Wee Kiat Tan - Setting u a Low-Cost Lab Management System fo a Multiuose Comuting Lab Using Vitualization Technology, Austalasian Jounal of Educational Technology, 8(), , (0). [KGP89] R. Katz, G. Gibson,. Patteson - is System Achitectue fo High Pefomance Comuting, Poceedings of the IEEE, Vol. 77, o., ec [MA8]. A. Menasce, V. A. Almeida - Oeational Analysis of Multiclass Systems with Vaiable Multiogamming Level and Memoy Queuing. Comute Pefomance, Vol. 3, o. 3, Set, 98. [WW00] Allen Wynn, Jie Wu - The Effect of Comession on Pefomance in a emand Paging Oeating Systems and Softwae, The Jounal of Systems and Softwae, 50 (000), [ZQ93] Xiaodang Zhang, agas allu Xiaohan Qin - A Tool fo Monitoing and Visualizing Min-Based Multiocesso Pefomance, Jounal of Paallel and istibuted Comuting, 8,. 3 4, 993.