CMPEN431-PractceExam1-SP17.pdf - Computer Science and...

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Computer Science and Engineering 431 Spring 2017 PRACTICE QUESTIONS for EXAM 1 Tuesday, February 28 th Exam time: 50 minutes/part x 2 parts Test Value: XX pts. Total possible points: YY ( max score = ZZ%) 1. Understanding Performance (P pts) Assume that machines A, B, C, and D implement the same ISA. a) Machine A runs at frequency F A and Machine B runs at frequency F B . For a given program P1 on input FOO, Machine A executes I A instructions with CPI C A and Machine B executes I B instructions with CPI C B . If Machine A has twice the performance of Machine B when executing P1(FOO), what is the ratio of frequencies of Machine A/Machine B expressed in terms of the other variables? . F A /F B = _______________________________________________________________ b) For a program P2 on input QUUX, Machine C and Machine D have the same performance. For a different input to program P2, BAR, Machine C is twice as fast as Machine D despite the same number of instructions being executed on all machines for all inputs. Of instruction count, frequency and CPI, explain which factor(s) are most likely responsible for the difference in performance as a function of inputs to P2, and why. Describe at least one plausible cause for the difference. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________
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2. Pipelining and data hazards (P pts) a) Consider the following sequence of instructions scheduled on a five stage, scalar MIPS pipeline. In the table below, for each cycle, indicate the cycle an instruction completes a stage with a capital letter (FDXMW) and indicate stalls with a lower case letter (fdxmw) in a circle. Assume full forwarding/bypass networks. Indicate by drawing a vertical arrow when a value is bypassed from one instruction to another in the cycle that the forwarding occurs . For simplicity, elide W à D bypassing arrows. Use the grid on the following page. Assume all loads/stores are
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  • Fall '10
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