For each of the memory reference streams given in the following,
compare the cost of executing
it on a bus-based machine that supports (a) the MESI protocol and (b) the Dragon protocol.
Explain the observed performance differences in terms of the characteristics of the streams and
the coherence protocols.
a. Stream 1: r1 w1 r1 w1 r2 w2 r2 w2 r3 w3 r3 w3
b. Stream 2: r1 r2 r3 w2 w2 w3 r1 r2 r3 w3 w1
c. Stream 3: r1 r2 r3 r3 w1 w1 w1 w1 w2 w3
All of the references in the streams are to the same location: r/w indicates read or write, and the
digit refers to the processor issuing the reference. Assume that all caches are initially empty, and
use the following cost model: read/write cache hit – 1 cycle; misses requiring simple transaction
on bus (BusUpgr, BusUpd) – 60 cycles; and misses requiring whole cache block transfer – 90
cycles. Assume all caches are write allocated.