Although a store-in cache requires less storage bandwidth
than that of a store-through cache, a shared storage bus can
become congested in the MP configuration. In order to estimate the bus traffic on the shared storage bus, a simple
queuing model was constructed, as shown in Figure 5. In that
model, the memory requests of a CPU to the main storage is
simulated as a Poisson process with the arrival rate determined by the cache miss ratio. The average number of bus
cycles for each bus access is computed by weighing the bus
cycles of each transaction with its corresponding probability.
A bus transaction can be a bus read miss, bus write miss, and
bus invalidation. It may incur a cache-to-cache transfer or a
storage access. The simulation results are shown in Table 2.
In this simulation, the CPU is assumed to achieve 3