A Comparison of Operating Systems Features in PowerPC versus x86

1
A Comparison of Operating Systems Features in
PowerPC versus x86

• Jason Gilanfarr
• CS 591 (OS 2)
• Spring 2004

2
Motivation

• PowerPC is available in more forms than x86. It
  powers many forms of embedded processors, desktop
  systems, and even super computers using the same
  basic architecture.
• Gain a clear understanding of the PowerPC
  architecture in order to port the User-Level
  Sandbox to another architecture.
• Investigate the hardware features allowing for a
  kernel to minimize its overhead.

3
Related Work

• Linux on the PowerPC Optimizing Modern Operating
  Systems for Modern Processors. Cort Dougan.
• Optimizing the Idle Task and Other MMU Tricks.
  Cort Dougan.
• Investigates the MMU architecture of 603 and 604
  PowerPCs. Uses hardware to gain overall
  improvement of 10-20.
• Improved Address Space Switching on Pentium
  Processors by Transparently Multiplexing User
  Address Spaces. Jochen Leidtke.
• Shows that address space switch overhead can be
  minimized by utilizing 2 virtual address space.

52
4
Approach

• Studied Hardware Manuals for 32-bit PPC,
  Motorollas G4 manuals, and the Operating System
  Manual for PowerPC processors (IBM).
• Investigated Kernel 2.4s and 2.6s use of the
  architecture by studying the assembly macros and
  writing modules to read/verify settings in the
  hardware registers.
• Investigated the use of the different methods of
  address translation to minimize the overhead of
  User-Level Sandboxing by keeping the number of
  TLB entries to a minimum.
• Gained knowledge of the split MMU present on all
  32-bit PowerPC processors. Most 64-bit PPCs have
  similar MMUs.

5
Results

• All tests performed using the Motorolla G4 (MPC
  7547) 1.33 GHz. Tests were performed using C and
  hardware timers or lmbench 3.0.
• Pipe Bandwidth 540.4 MB/s
• Null Syscall overhead 0.075µs
• 2 Process Context Switch Overhead 0.667µs

6
Future Work / Conclusions

• Finish Implementing Pure Upcalls into user code.
• Use the MMU methods and upcalling code to
  implement the User-Level Sandbox in a portable
  manner.
• The PowerPC architecture is fundamentally
  different from x86, although most code can be
  ported utilizing some of the features of the
  architecture. Optimization techniques can be
  utilized without sacrificing portability.