[Chapter2] Cosmetics. part6

chapters/2-Measuring-Performance/2-0 Measuring Performance.md

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 # Measuring Performance {#sec:secMeasPerf}
 
-The first step to understanding the performance of an application is to measure it. Anyone ever concerned with performance evaluations likely knows how hard it is sometimes to conduct fair performance measurements and draw accurate conclusions from them. Performance measurements can be very unexpected and counterintuitive. Changing a seemingly unrelated part of the source code can surprise us with a significant impact on the performance of the program. For various reasons, performance measurements may consistently overestimate or underestimate the true value, which leads to distorted results that do not accurately reflect reality. This phenomenon is called *measurement bias*. 
+The first step to understanding the performance of an application is to measure it. Anyone ever concerned with performance evaluations likely knows how hard it is sometimes to conduct fair performance measurements and draw accurate conclusions from them. Performance measurements can be very unexpected and counterintuitive. Changing a seemingly unrelated part of the source code can surprise us with a significant impact on the performance of the program. For various reasons, measurements may consistently overestimate or underestimate the true performance, which leads to distorted results that do not accurately reflect reality. This phenomenon is called *measurement bias*.
 
 Performance problems are often harder to reproduce and root cause than most functional issues. Every run of a program is usually functionally the same but somewhat different from a performance standpoint. For example, when unpacking a zip file, we get the same result over and over again, which means this operation is reproducible. However, it's impossible to reproduce the same CPU cycle-by-cycle performance profile of this operation.