An infrastructure for multiprocessor run-time adaptation

Runtimeadaptationanddynamicrecon gurationallowasystemtodynamicallyswapinthemostappropriateimple-mentationofitscomp onentsbasedoncurrentorexp ecteduse,andtoselectivelyupgradecomp onentswithbug,secu-rity,orp erformance xeswithoutdown-time.Hot-swappingistheactofreplacinganactivesystemcomp onent'sim-plementationwithanewordi erentimplemenwhilemaintainingavailabilityofthecomp onent'sfunctionalit.Thispap erdescrib esamechanism tohot-swapsoftwarecom-p onentswithintheK421op eratingsystem.Wehavusedthiscapabilitytoimprovep erformanceunderaarietofconditions.K42isaresearchop eratingsystemforcache-coherentsharedmemorymultipro cessorsdesignedtoachievego o dscalabilityonawiderangeofworkloads.InK42,eachvir-tualandphysicalresource,e.g.,op en le,memoryregion,pagetable,ismanagedbyseparate, ne-granularit,ob jectinstances.Eachob jectinstancemayb ecustomized(di er-entsub-class).Thismo delprovidesthestandardsoftwareengineeringb ene ts,butmoreimp ortantly:1)allowsp er-formancecustomizationonanob ject-by-ob jectbasisand2)allows,onamultipro cessor,indep endentaccessestob edirectedtoindep endentinstancesandpro ceedinparallelthuseliminatingsharedmemoryaccessesandsynchroniza-tion,whicharefundamentalbarrierstomultipro cessorp er-formance.Anop eratingsystemisaparticularlydemandingenvi-ronmentasitneedstosatisfymultipleconcurrenclientswhoseresourcedemandsmayb eato dds.Forexample,multipleclientsmaysimultaneouslyaccessa lewithdif-ferentusagepatterns.Supp ortingmultipro cessorspresentsadditionalchallengesforop eratingsystems,andoftenimple-mentationsthatarerequiredforscalablep erformancehaveworseunipro cessorb ehavior.Toprovideb othunipro cessorandmultipro cessorcomp o-nentswithinasingleob jectmo del,K42'sob jectsareim-1http://www.research.ibm.com/K42