Preventing Performance Degradation

on Operating System Reboots

Kenichi Kourai

Tokyo Institute of Technology

Motivation

OS reboot is not avoidableMany bugs in OSesSimple method for software

rejuvenation

Performance degradation after OS rebootThe file cache is lostDisk access conflicts between

virtual machines (VMs)

VM VM

sharedphysical disk

Warm-cache Reboot

A new reboot mechanism to prevent the performance degradationEnables an OS to reuse the file cachePreserves the integrity of the file cache

Our claimThe file cache does not need to be

discarded if its integrity is preservedThe purpose of OS reboot is to initialize its

internal state or to update its components

The warm-cache reboot preserves cache pages on memory during OS rebootThe VMM allocates the same memory

to VMsThe OS maintains a cache-mapping

table

Preserving the File Cache

virtual machine monitor (VMM)

cache-mappingtable

OS

cache pageVM

Protecting the File Cache

Cache pages are write-protectedThe VMM reads file blocks into a

protected cache pageThe VMM maintains a reuse flag

diskvirtual machine monitor (VMM)

OS

VM

write-protected

readset a reuse flag

Experiment

Power test in DBT-3To examine the

performance just afterOS reboot

ResultsWarm-cache reboot

No performance degradation

Normal rebootDegraded by 67%

before after

VMM: Xen 3.0.0OS: Linux 2.6.12CPU: dual-core Opteron x2Memory:12 GBDisk: Ultra SCSI

Conclusion

We proposed the warm-cache rebootPreserves the file cache during OS

rebootProtects cache pages using the VMM

Related workRio file cache [Chen et al.'96]

Preserves dirty file cache for reliability Warm-VM reboot [Kourai et al. '07]

Preserves VMs during VMM reboot