[CSE]  Advanced Operating Systems 
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Next: -kernel Design Principles Up: 05-uk Previous: Critique of Microkernel Architectures

Subsections

A Critique of the Critique

Data presented earlier:
  • are specific to one (or a few) system,
  • results cannot be generalised without thorough analysis,
  • no such analysis has been done.
==> Cannot trust the conclusions[Lie95].

Re-analysis of Chen & Bershad's Data


l_95_f3
MCPI for Ultrix and Mach

Re-analysis of Chen & Bershad's Data...


l_95_f4

MCPI caused by cache misses: conflict (black) vs capacity (white)

Conclusion

 $.$
Mach system (kernel + UNIX server + emulation library) is too big!
 $.$
UNIX server is essentially same.
 $.$
Emulation library is irrelevant (according to Chan & Bershad).
==>
Mach \(\mu\)-kernel working set is too big





Can we build \(\mu\)-kernels which avoid these problems?

Requirements for \(\mu\)-kernels:

 $.$
Fast (system call costs, IPC costs)
 $.$
Small (big ==> slow)
==>
Must be well designed, providing a minimal set of operations.





Can this be done?

Are high system costs essential?

  • Example: kernel call cost on i486
     ${}$
    Mach kernel call: 900 cycles
     ${}$
    Inherent (hardware-dictated cost): 107 cycles.
    ==> 800 cycles kernel overhead.
     ${}$
    L4 kernel call: 123-180 cycles (15-73 cycles overhead).
    ==>
    Mach's performance is a result of design and implementation
    not the \(\mu\)-kernel concept!


next up previous
Next: -kernel Design Principles Up: 05-uk Previous: Critique of Microkernel Architectures
Gernot Heiser 2002-08-28