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Page 447 Note that g is (usually) not the physical buffer size; rather, it is the mean expected bypassed request queue per source. Finding g allows us to properly implement the physical buffer. Recall that: and the queue per module for the By increasing the number of bypass registers, we realize a larger effective g. We can continue this until there is no contention, so: Let us call this value of g, which eliminates contention, g = gopt. We can find this by observing that "no contention" occurs when B = n, or: This occurs when (assuming m > n): Substituting Equation 7.6 into Equation 7.3 (p = 1/m), we get: but rearranging Equation 7.4, since n= B at gopt. Then: At gopt: mQ = ngopt. Thus, the mean total buffer size (TBF) is ngopt. Recall that any physical buffer that avoids overflow must be considerably larger (chapter 4), e.g.:
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