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1、第 2 讲：OS Architecture&Structure第四节：Micro kernel Mach&L4What is a Microkernel?Kernel with minimal featuresMoves as much from the kernel into user spaceAddress spacesInterprocess communication(IPC)Scheduling.What is a Microkernel?BenefitsFlexibilitySafetyModularityDetrimentsAddress spacesInterprocess
2、communication(IPC)Scheduling.Microkernel MachMach Developed at CMU Led by Rick Rashid,Founded Microsoft Research Initial release:1985First generation microkernel Mach(led by RickRashid)Task and thread managementTask(process)unit of allocationThread,unit of executionCPU scheduling policies exposed to
3、 appsInterprocess communication(IPC)Between threads via portsSecured by capabilitiesMemory object managementvirtual memorymemory objecthierarchical pagers.Microkernel MachFirst generation microkernel Mach.Microkernel MachFirst generation microkernel MachPerformancethe use of IPC for almost all tasks
4、 turned out tohave serious performance impact.system calls take 5-6X as long as UNIXgiven a syscall that does nothing,a full round-tripunder BSD would require about 40s,whereas on auser-space Mach system it would take just under500s.benchmarks on 1997 hardware showed that Mach3.0-based UNIX single-s
5、erver implementations wereabout 50%slower than native UNIX.Microkernel L4Second generation microkernel L4 by JochenLiedtke(GMD)Performancesynchronous IPCs async IPCs(like epoll in Linux)smaller,Mach 3(330 KB)L4(12KB)IPC security checks moved to user processIPC is hardware dependent.L4 family.L4 family.L4 family.