Parallel Computer Architecture

596 CHAPTER 8 Directory-Based Cache Coherence

have performance disadvantages, and for protocols that do not do this, avoiding

starvation can be difficult to guarantee. Deadlock or livelock solutions that use

NACKs and retries are often more susceptible to starvation, which is most likely

when many processors repeatedly compete for a resource. Some may keep succeed-

ing while one or more may be very unlucky in their timing and may always get

NACKed.

A protocol could decide to do nothing about starvation and rely on the variability

of delays in the system not to allow such an indefinitely repeating pathological situ-

ation to occur. The DASH machin ...