Revision MIPS Pipelined Architecture

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Walter Pierce
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1 Rviion MIPS Piplin Achitctu D. Eng. Am T. Abl-Hami ELECT 1002 Sytm-n-a-Chip Dign Sping 2009 MIPS: A "Typical" RISC ISA 32-bit fix fomat intuction (3 fomat) bit GPR (R0 contain zo, DP tak pai) 3-a, g-g aithmtic intuction Singl a mo fo loa/to: ba + iplacmnt no iniction Simpl banch conition Dlay banch : SPARC, MIPS, HP PA-Ric, DEC Alpha, IBM PowPC, CDC 6600, CDC 7600, Cay-1, Cay-2, Cay-3

2 Exampl: MIPS (- MIPS) it-it p R1 R2 R px it-immiat p R1 R immiat Banch p R1 R2/px immiat Jump / Call p tagt Datapath v Contol Datapath Contoll ignal Contol Point Datapath: Stoag, FU, intconnct ufficint to pfom th i function Input a Contol Point utput a ignal Contoll: Stat machin to ochtat opation on th ata pat h Ba on i function an ignal

3 5 Stp of MIPS Datapath Nxt PC Intuction Ftch 4 A Int. Dco. Ftch Nxt SEQ PC RS1 Excut A. Calc Zo? Mmoy Acc MUX Wit Back A Mmoy Int RS2 RD Fil MUXMUX Data Mmoy L M D MUX Imm Sign Extn What I Piplining Launy Exampl Ann, Bian, Cathy, Dav ach hav on loa of cloth to wah, y, an fol Wah tak 30 minut A B C D Dy tak 40 minut Fol tak 20 minut

4 T a k What I Piplining A B C D 6 PM Minight Tim Squntial launy tak 6 hou fo 4 loa If thy lan piplining, how long woul launy tak? What I Piplining Stat wok ASAP 6 PM Minight Tim T a k A B C D Piplin launy tak 3.5 hou fo 4 loa 8

5 What I Pip lining T a k A B C D 6 PM Tim Piplining Lon Piplining on t hlp latn cy of ingl tak, it hlp th oughput of nti wokloa Piplin at limit by low t piplin tag Multipl tak opating im ultanouly Potntial pup = Numb pip tag Unbalanc lngth of pip tag uc pup Tim to fill piplin an ti m to ain it uc p up 5 Stp of MIPS Datapath Figu A.3, Pag A-9 Nxt PC A Intuction Ftch 4 A Mmoy IF/ID Int. Dco. Ftch Nxt SEQ PC RS1 RS2 Imm Fil Sign Extn ID/EX Excut A. Calc Nxt SEQ PC MUXMUX Zo? EX/MEM RD RD RD Mmoy Acc MUX Data Mmoy MEM/WB Wit Back MUX WB Data

6 I n t. Viualizing Piplining Figu A.2, Pag A-8 Tim (clock cycl) Cycl 1 Cycl 2 Cycl 3 Cycl 4 Cycl 5 Cycl 6 Cycl 7 What I Piplining Intuction Ftch (IF): Sn out th PC an ftch th intuction fom mmoy into th intuction git (IR); inc mnt th PC by 4 to a th nxt qunti al intuction. IR hol th intuction that will b u in th nxt tag. NPC hol th valu of th nxt PC. Intuction Dco/it Ftch Cyc l (ID): Dco th intuction an acc th git fil t o a th git. Th output of th gnal pupo git a a into two tmpoay git (A & B) fo u in la t clock cycl. W xtn th ign of th low 16 bit of th Int uction it. IR <- < Mm[PC] NPC <- < PC + 4 A <- < [IR6..IR..IR10 10]; B <- < [IR IR..IR15 15]; Imm <- < ((IR16 16) ) ##IR

7 What I Piplining Excut A Calculation (EX): W pfom an opation (fo an ) o an a calculation (if it a loa o a Banch). If an, actually o th opation. If an a calculation, figu out how to obtain th a an tah away th location of that a fo th nxt cycl. MEMRY ACCESS (MEM): If thi i an, o nothing. If a loa o to, thn acc mmoy. WRITE BACK (WB): Upat th git fom ith th o fo m th ata loa. A <- < A func. B con = 0; A = Mm[pv. B] o Mm[pv. B] = A <- < A, B; Piplining i not quit that ay! Limit to piplining: Haza pvnt nxt intuction fom xcuting uing it ignat clock cycl Stuctual haza: HW cannot uppot thi combination of in tuction (ingl pon to fol an put cloth away) Data haza: Intuction pn on ult of pio intuctio n till in th piplin (miing ock) Contol haza: Cau by lay btwn th ftching of in tuction an ciion about chang in contol flow (banch an jump).

8 n Mmoy Pot/Stuctual Haza Figu A.4, Pag A-14 Tim (clock cycl) Cycl 1 Cycl 2 Cycl 3 Cycl 4 Cycl 5 Cycl 6 Cycl 7 I Loa n Int 1 t. Int 2 Int 3 Int 4 n Mmoy Pot/Stuctual Haza (Simila to Figu A.5, Pag A-15) I n t. Tim (clock cycl) Loa Int 1 Int 2 Stall Cycl 1Cycl 2Cycl 3Cycl Cycl 4 5Cycl 6Cycl 7 Int 3 Bubbl BubblBubblBubblBubbl

9 Sp Up Equation fo Piplining CPI piplin = Ial CPI + Avag Stall cycl p Int Ial CPI Piplin pth Spup = Ial CPI + Piplin tall CPI Cycl Cycl Tim Tim unpiplin piplin Fo impl RISC piplin, CPI = 1: Piplin pth Spup = 1+ Piplin tall CPI Cycl Cycl Tim Tim unpiplin piplin Exampl: Dual-pot v. Singl-pot Machin A: Dual pot mmoy ( Hava Achitctu ) Machin B: Singl pot mmoy, but it piplin implmnt ation ha a 1.05 tim fat clock at Ial CPI = 1 fo both Loa a 40% of intuction xcut 5) SpUp A = Piplin Dpth/(1 + 0) x (clock unpip /clock pip ) = Piplin Dpth SpUp B = Piplin Dpth/( x 1) x (clock unpip /(clock unpip / 1.0 = (Piplin Dpth/1.4) x 1.05 = 0.75 x Piplin Dpth SpUp A / SpUp B = Piplin Dpth/(0.75 x Piplin Dpth) = 1.33 Machin A i 1.33 tim fat

10 Data Haza on R1 Figu A.6, Pag A-17 I n t. Tim (clock cycl) IF ID/RF EX MEM WB a 1,2,3 ub 4,1,3 an 6,1,7 o 8,1,9 xo 10,1,11 Th Gnic Data Haza Ra Aft Wit (RAW) Int J ti to a opan bfo Int I wit it I: a 1,2,3 J: ub 4,1,3 Cau by a Dpnnc (in compil nomnclatu). Thi haza ult fom an actual n fo communication.

11 Th Gnic Data Haza Wit Aft Ra (WAR) Int J wit opan bfo Int I a it I: ub 4,1,3 J: a 1,2,3 K: mul 6,1,7 Call an anti-pnnc by compil wit. Thi ult fom u of th nam 1. Can t happn in MIPS 5 tag piplin bcau: All intuction tak 5 tag, an Ra a alway in tag 2, an Wit a alway in tag 5 Th Gnic Data Haza Wit Aft Wit (WAW) Int J wit opan bfo Int I wit it. I: ub 1,4,3 J: a 1,2,3 K: mul 6,1,7 Call an output pnnc by compil wit Thi alo ult fom th u of nam 1. Can t happn in MIPS 5 tag piplin bcau: All intuction tak 5 tag, an Wit a alway in tag 5 Will WAR an WAW in mo complicat pip

12 Fowaing to Avoi Data Haza Figu A.7, Pag A-19 I n t. a 1,2,3 ub 4,1,3 Tim (clock cycl) an 6,1,7 o 8,1,9 xo 10,1,11 HW Chang fo Fowaing Figu A.23, Pag A-37 NxtPC it Immiat ID/EX mux mux EX/MEM Data Mmoy MEM/WR mux What cicuit tct an olv thi haza?

13 Fowaing to Avoi LW-SW Data Haza Figu A.8, Pag A-20 I n t. a 1,2,3 lw 4, 0(1) Tim (clock cycl) w 4,12(1) o 8,6,9 xo 10,9,11 Data Haza Evn with Fowaing Figu A.9, Pag A-21 Tim (clock cycl) I n t. lw 1, 0(2) ub 4,1,6 an 6,1,7 o 8,1,9

14 Data Haza Evn with Fowaing (Simila to Figu A.10, Pag A-21) I n t. Tim (clock cycl) lw 1, 0(2) ub 4,1,6 an 6,1,7 Bubbl Bubbl o 8,1,9 How i thi tct? Bubbl Contol Haza on Banch Th Stag Stall 10: bq 1,3,36 14: an 2,3,5 18: o 6,1,7 22: a 8,1,9 36: xo 10,1,11

15 Banch Stall Impact If CPI = 1, 30% banch, Stall 3 cycl => nw CPI = 1.9! Two pat olution: Dtmin banch takn o not oon, AND Comput takn banch a ali MIPS banch tt if git = 0 o 0 MIPS Solution: Mov Zo tt to ID/RF tag A to calculat nw PC in ID/RF tag 1 clock cycl pnalty fo banch vu 3 Piplin MIPS Datapath Figu A.24, pag A-38 Nxt PC Intuction Ftch 4 A Int. Dco. Ftch Nxt S EQ PC A RS1 MUX Zo? Excut A. Calc Mmoy Acc Wit Back A Mmoy IF/ID Fil Sign Extn MUX EX/MEM RD RD RD Intplay of intuction t ign an cycl tim. RS2 Imm ID/EX Data Mmoy MEM/WB MUX WB Data

16 Fou Banch Haza Altnativ #1: Stall until banch iction i cla #2: Pict Banch Not Takn Excut ucco intuction in qunc Squah intuction in piplin if banch actually takn Avantag of lat piplin tat upat 47% MIPS banch not takn on avag PC+4 alay calculat, o u it to gt nxt intuction #3: Pict Banch Takn 53% MIPS banch takn on avag But havn t calculat banch tagt a in MIPS MIPS till incu 1 cycl banch pnalty th machin: banch tagt known bfo outcom Fou Banch Haza Altnativ #4: Dlay Banch Dfin banch to tak plac AFTER a following intuction banch intuction quntial ucco 1 quntial ucco 2... quntial ucco n banch tagt if takn Banch lay of lngth n 1 lot lay allow pop ciion an banch tagt a in 5 tag piplin MIPS u thia

17 Schuling Banch Dlay Slot (Fig A.14) A. Fom bfo banch B. Fom banch tagt C. Fom fall though a $1,$2,$3 if $2=0 thn lay lot ub $4,$5,$6 a $1,$2,$3 if $1=0 thn lay lot a $1,$2,$3 if $1=0 thn lay lot ub $4,$5,$6 bcom bcom bcom a $1,$2,$3 if $2=0 thn if $1=0 thn A i th bt choic, fill lay lot & uc intuction count (IC) In B, th ub intuction may n to b copi, incaing IC In B an C, mut b okay to xcut ub whn banch fail a $1,$2,$3 a $1,$2,$3 if $1=0 thn ub $4,$5,$6 ub $4,$5,$6 Dlay Banch Compil ffctivn fo ingl banch lay lot: Fill about 60% of banch lay lot About 80% of intuction xcut in banch lay lot u ful in computation About 50% (60% x 80%) of lot ufully fill Dlay Banch owni: A poco go to p pi plin an multipl iu, th banch lay gow an n mo than on lay lot Dlay banching ha lot populaity compa to mo xpniv but mo flxibl ynamic appoach Gowth in availabl tanito ha ma ynamic appoac h lativly chap

18 Pojct Plan??

Instruction Execution

Instruction Execution MIPS Piplining Cpt280 D Cuti Nlon Intuction Excution C intuction: x = a + b; Ambly intuction: a a,b,x Stp 1: Stp 2: Stp 3: Stp : Stp 5: Stp 6: Ftch th intuction Dtmin it i an a intuction Ftch th ata a