STATIC SOFTWARE SCHEMES Generational approach

Generational approach

• Chiueh, 1993, the State University of New York at Stony Brook
• Essence: determination of the last "valid" task generation
• HW support:
  • Each cache line is extended with a VGN field
  • A new register per processor is added, to indicate the CGN of running tasks
• SW support:
  • Instruction to set VGN(X) is inserted by compiler at the end of task which writes to X
• Algorithm:
  • VGN(X):= number of task generation in which the X is written again
  • CGN register is set when a task is scheduled to a processor
  • if VGN(X) >= CGN => hit
• Simplified hardware support (one CGN versus many CVNs)
• Natural solution to DoAccross loops and conditional writes