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Unformatted text preview: active? 458 CHAPTER 9. MEASURING PROGRAM EXECUTION TIME
Intel Pentium III, Linux, Process Timer
0.5 0.4 0.3 Measured:Expected Error 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 0 50 100 150 200 250 300 Expected CPU Time (ms) Load 1 Load 11 Figure 9.8: Experimental Results for Measuring Interval Counting Accuracy. The error is unacceptably high when measuring activities less than around 100 ms (10 timer intervals). Beyond this, the error rate is generally less than 10% regardless of whether running on lightly loaded (Load 1) or heavily loaded (Load 11) machine. For programs that run long enough, (at least several seconds), the inaccuracies in this scheme tend to compensate for each other. The execution times of some segments are underestimated while those of others are overestimated. Averaged over a number of segments, the expected error approaches zero. From a theoretical perspective, however, there is no guaranteed bound on how far these measurements vary from the true run times. To test the accuracy of this timing method, we ran a serie...
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