Pipeline Questions
Printed From: One Stop GATE
Category: GATE Technical Discussions
Forum Name: GATE CS
Forum Discription: General Technical Discussions, Queries, doubts etc. for GATE in CS.
URL: http://forum.onestopgate.com/forum_posts.asp?TID=534
Printed Date: 19Apr2025 at 11:38pm
Topic: Pipeline Questions
Posted By: manju
Subject: Pipeline Questions
Date Posted: 22Feb2007 at 2:25pm
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1. Consider the case of a computer system employing both a cache and a paged virtual memory . One can analyze this system through identifying FIVE combinations of accesses. What are these combinations? Determine the probability and the access time in each case assuming the following information. Compute also the overall average access time. TLB address translation and search 25 ns Cache search time to determine whether address in cache 25 ns Cache access time 25 ns Main memory access time 250 ns Hard disk access time 100 ms TLB hit ratio 0.9 Cache hit ratio 0.95 Main memory hit ratio 0.8 2. Consider the execution of 500 instructions on a five-stage pipeline machine. Compute the speed-up due to the use of pipelining given that the probability of an instruction being a branch is p = 0.3? What must be the value of p and the expected number of branch instructions such that a speed-up of at least 4 is possible? What must be the value of p such that a speed-up of at least 5 is possible? Assume that each stage takes one cycle to perform its task. Plz try to solve this questions ??? 
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Replies:
Posted By: balu
Date Posted: 22Feb2007 at 2:27pm
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I can proceed wth few steps as folows: In pipeline, 500 instructions, w/o any branch, they will take 500 clock cycles Now, 500*0.3 are branch instr, assuming branch instr stalls the pipeline for remaining stages till its execution is complete (coz no behaviour regarding ths is given  ) so they will take 500*0.3*(1 : for fetch + 4 : delayed) = 500 * 0.3 * 5 Remaining will execute normally i.e. 500*0.7 will take same amnt.. so avg = 500 * 0.7 + 500 * 0.3 * 5 = 750 as opposed to 500 when no branch..  (i doubt abt ths.. ) so speed up = 1.5  plz chk n correct.. i guess m mising some details..
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