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Unformatted text preview: fferent degrees of unrolling, and for two different vector lengths we obtain the following: Vector Length CPE 31 Net CPE 1024 Net CPE 1 2.00 4.02 2.06 Degree of Unrolling 2 3 4 8 1.50 1.33 1.50 1.25 3.57 3.39 3.84 3.91 1.56 1.40 1.56 1.31 16 1.06 3.66 1.12 The distinction between CPE and net CPE is minimal for long vectors, as seen with the measurements for length 1024, but the impact is signiﬁcant for short vectors, as seen with the measurements for length 31. Our measurements of the net CPE for a vector of length 31 demonstrate one drawback of loop unrolling. Even with no unrolling, the net CPE of 4.02 is considerably higher than the 2.06 measured for long vectors. The overhead of starting and completing the loop becomes far more signiﬁcant when the loop is executed a smaller number of times. In addition, the beneﬁt of loop unrolling is less signiﬁcant. Our unrolled code must start and stop two loops, and it must complete the ﬁnal elements one at a time. The overhead decreases with increased loop unrolling, while the number of operations performed in the ﬁnal loop increases. With a vector length of 1024, performance generally improves as the degree of unrolling increases. With a vector length of 31, the best performance is achieved by unrolling the loop by...
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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.
- Spring '10
- The American