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Unformatted text preview: er case, the resolution will be poor—no better than what is provided by functions times and clock. Figure 9.21 also shows the latency required by a call to get timer on various systems. This property indicates the minimum time required for a call to the function. We computed this by repeatedly calling the function until one second had elapsed and dividing 1 by the number of calls. As can be seen, this function requires around 1-microsecond on most systems, and several microseconds on others. By comparison, our procedure get counter requires only around 0.2 microseconds per call. In general, system calls involve more overhead than ordinary function calls. This latency also limits the precision of our measurements. Even if the data structure allowed expressing time in units with higher resolution, it is unclear how much more precisely we could measure time when each measurement incurs such a long delay. Figure 9.22 shows the performance we get from an implementation of the à -best measurement scheme using gettimeofday rather than our own functions to access the cycle counter....
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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