4 votes 4 votes Consider a 5 stage pipeline with IF, ID, EX, MEM and WB latencies 8, 6, 4, 6 and 4 respectively (in ns). If IF stage is made 50% faster, the percentage it will improve the performance CPU is __________. tiger asked Dec 20, 2015 tiger 3.0k views answer comment Share Follow See all 3 Comments See all 3 3 Comments reply Vinay Yadav commented Dec 20, 2015 i edited by Vinay Yadav Dec 20, 2015 reply Follow Share is it 33% 2 votes 2 votes Jevi commented Dec 29, 2015 reply Follow Share Which is the correct answer? 33% or 25% .. Can u explain please 0 votes 0 votes Morphine commented Dec 31, 2015 i edited by Morphine Dec 31, 2015 reply Follow Share Performance is based on clock cycles. in first case since its a non-uniform , the clock cycle will be fixed with the highest latency i.e C = 8 ns in 2nd case due to 50% increment latency of IF = 4ms. In this case the highest latency becomes C = 6ns Thus, Decrement is from 8ns to 6ns is (6-8)/8 *100 = 25% In Case if you are confused about the percentage calculation check this : http://www.calculatorcat.com/free_calculators/percent_gain.phtml 3 votes 3 votes Please log in or register to add a comment.
1 votes 1 votes In case of pipeline we have to consider maximum stage delay as uniform delay so in normal case time taken to execute an instruction will be '8ns' as it is highest time taken by IF. Now as per question IF is becoming 50% faster so new delay for IF stage will be '4ns'. So average time taken by an instruction in second case is max(4,6,4,6,4). which is '6ns' %performance increased = (8-6/8)*100 = 25% mayursheliya answered Sep 19, 2018 mayursheliya comment Share Follow See all 0 reply Please log in or register to add a comment.