Fundamentals of Quantitative Design and Analysis - Computer Architecture: A Quantitative Approach - page 45

Example
Show that the ratio of the geometric means is equal to the geometric mean of
the performance ratios, and that the reference computer of SPECRatio matters
not.
Answer
Assume two computers A and B and a set of SPECRatios for each.
That is, the ratio of the geometric means of the SPECRatios of A and B is the
geometric mean of the performance ratios of A to B of all the benchmarks in the
suite. Figure 1.17 demonstrates this validity using examples from SPEC.
1.9 Quantitative Principles of Computer Design
Now that we have seen how to define, measure, and summarize performance, cost, dependab-
ility, energy, and power, we can explore guidelines and principles that are useful in the design
and analysis of computers. This section introduces important observations about design, as
well as two equations to evaluate alternatives.
Take Advantage Of Parallelism
Taking advantage of parallelism is one of the most important methods for improving perform-
ance. Every chapter in this topic has an example of how performance is enhanced through
the exploitation of parallelism. We give three brief examples here, which are expounded on in
later chapters.
Our first example is the use of parallelism at the system level. To improve the throughput
performance on a typical server benchmark, such as SPECWeb or TPC-C, multiple processors
and multiple disks can be used. The workload of handling requests can then be spread among
the processors and disks, resulting in improved throughput. Being able to expand memory
and the number of processors and disks is called scalability , and it is a valuable asset for serv-
ers. Spreading of data across many disks for parallel reads and writes enables data-level paral-