[理工] 計組pipeline問題

看板Grad-ProbAsk作者qwer123073 (NullSpace)時間9年前 (2017/01/22 00:03)推噓6(6推 0噓 17→)

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想問各位高手一些pipeline的問題問題一： For the code sequence below,assume the two bne instructions are as taken,but actually they are not taken.How many cycles does it take to complete the execution of the code by using the two CPUs below,respectively?For each CPU,please also identify which cycle(s) will become bubble(i.e., stall cycle) when executes the code(Note:the first instruction:"lw $t0,$s1,$s2 "starts from cycle 1). 1. lw $t0,$s1,$s2 2. add $s0,$t0,$t1 3. lw $s1,0($t0) 4. bne $s0,$s1,10 5. add $s2,$s0,$s1 6. add $s3,$s1,$s0 7. bne $s2,$s3,10 8. add $s3,$s2,$s3 (1)The pipelined CPU for which assume the forwarding mechanism has been designed and the branch outcome is determined at MEM stage. (2)The pipelined CPU for which assume the forwarding mechanism has been designed and some hardware has been added to determine the branch outcome at ID stage. 以下為答案： (1) Total number of cycles = 5-1+8+1+1+3+3=20 Stall cycles : c4,c7 (2) Total number of cycles = 5-1+8+1+2+1+1+1=18 Stall cycles : c4,c7,c8,c12 以下是我的想法 (1) IF ID EX ME WB --lw $t0,$s1,$t2 IF ID ID EX ME WB --add $s0,$t0,$t1 IF IF ID EX ME WB --lw $s1,0($t0) IF ID ID EX ME WB --bne $s0,$s1,10 IF IF ID EX ME WB --add $s2,$s0,$s1 以上因為有2個load-use hazards 所以共stall 2 cycles 題目中提到 bne猜會跳但是其實沒跳我想問 5-1+8+1+1+3+3 後面兩個3是怎麼算的 (2) IF ID EX ME WB --lw $t0,$s1,$t2 IF ID ID EX ME WB --add $s0,$t0,$t1 IF IF ID EX ME WB --lw $s1,0($t0) IF ID ID ID EX ME WB --bne $s0,$s1,10 IF IF IF ID EX ME WB --add $s2,$s0,$s1 跟第一題一樣我知道load-use共stall (1+2) cycles 但是不知道後面bne的部分要怎麼看還請大家指點問題二：想問stall和nop的使用時機什麼時候用stall 什麼時候用nop 謝謝大家 -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 36.239.41.152 ※ 文章網址: https://www.ptt.cc/bbs/Grad-ProbAsk/M.1485014629.A.1DF.html

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