ECE4680 Computer Organization and Architecture. Hazards in a Pipeline Processor. Pipeline is good but you need be careful.

Transcription

1 ECE4680 Compu gaizaio a Achicu Haza i a Pipli Poco Pipli i goo bu you b caful. ECE4680 Haza Pipliig: Naual! Lauy Exampl A, Bia, Cahy, Dav ach hav o loa of cloh o wah, y, a fol A B C D Wah ak 30 miu Dy ak 40 miu Fol ak 20 miu ECE4680 Haza

2 Squial Lauy 6 PM Miigh Tim T a k A B C D Squial lauy ak 6 hou fo 4 loa f hy la pipliig, how log woul lauy ak? ECE4680 Haza Pipli Lauy: Sa wok ASAP 6 PM Miigh Tim T a k A B C D Pipli lauy ak 3.5 hou fo 4 loa ECE4680 Haza

3 Pipliig Lo T a k 6 PM Tim A B C D Pipliig o hlp lacy of igl ak, i hlp houghpu of i wokloa Pipli a limi by low pipli ag Mulipl ak opaig imulaouly Poial pup = Numb of pip ag Ubalac lgh of pip ag uc pup Tim o fill pipli a im o ai i uc pup ECE4680 Haza Why o pipli fo iucio? ECE4680 Haza

4 Rviw: Sigl Cycl, Mulipl Cycl, v. Pipli Cycl 1 Cycl 2 Clk Sigl Cycl mplmaio: Loa So Wa Clk Cycl 1 Cycl 2 Cycl 3 Cycl 4 Cycl 5 Cycl 6 Cycl 7 Cycl 8 Cycl 9 Cycl 10 Mulipl Cycl mplmaio: Loa fch Rg Exc Mm W So fch Rg Exc Mm R-yp fch Pipli mplmaio: Loa fch Rg Exc Mm W So fch Rg Exc Mm W R-yp fch Rg Exc Mm W ECE4680 Haza Rviw: A Pipli Daapah Clk fch Rg/Dc Exc Mm W RgW Exp p Bach PC 1 0 PC+4 AUi F/D Rgi PC+4 mm16 R Ra Rb R RFil R Rw Di R D/Ex Rgi 0 1 PC+4 mm16 bua bub Exc Ui Ex/Mm Rgi Zo Daa Mm RA Do WA Di Mm/W Rgi 1 Mux 0 RgD Sc MmW MmoRg ECE4680 Haza

5 Rviw: Pipli Cool Daa Saioay Cool Th Mai Cool ga h cool igal uig Rg/Dc Cool igal fo Exc (Exp, Sc,...) a u 1 cycl la Cool igal fo Mm (MmW Bach) a u 2 cycl la Cool igal fo W (MmoRg MmW) a u 3 cycl la Rg/Dc Exc Mm W F/D Rgi Mai Cool Exp Sc p RgD MmW Bach MmoRg RgW D/Ex Rgi Exp Sc p RgD MmW Bach MmoRg RgW Ex/Mm Rgi MmW Bach MmoRg RgW Mm/W Rgi MmoRg RgW ECE4680 Haza Rviw: Pipli Summay Pipli Poco: Naual hacm of h mulipl clock cycl poco Each fucioal ui ca oly b u oc p iucio f a iucio i goig o u a fucioal ui: - i mu u i a h am ag a all oh iucio Pipli Cool: - Each ag cool igal p NLY o h iucio ha i culy i ha ag ECE4680 Haza

6 o ha ay fo compu Limi o pipliig: Haza pv x iucio fom xcuig uig i iga clock cycl Sucual haza (hawa ouc coflic): HW cao uppo hi combiaio of iucio (igl po o fol a pu cloh away) Daa haza (aa pci): ucio p o ul of pio iucio ill i h pipli (miig ock) Cool haza (chag i pogam flow): Pipliig of bach & oh iucio all h pipli uil h haza ( bubbl ) i h pipli iappa. ECE4680 Haza Sigl Mmoy i a Sucual Haza Tim (clock cycl). Loa Mm Rg Mm Rg Mm Rg Mm Rg Mm Mm Rg Mm Rg Rg Mm Rg Mm Rg Mm Rg ECE4680 Haza

7 pio 1: Sall o olv Mmoy Sucual Haza Tim (clock cycl). Loa 1 2 3(all) 4 Mm Rg Mm Rg Mm Rg Mm Rg Mm Rg Mm Rg bubbl Mm Rg Mm Rg Mm Rg Mm Rg ECE4680 Haza pio 2: Duplica o Rolv Sucual Haza Spaa ucio Cach (m) & Daa Cach (Dm) Tim (clock cycl). Loa m Rg Dm Rg ECE4680 Haza

8 Daa Haza o 1 a 1,2,3 ub 4, 1,3 a 6, 1,7 o 8, 1,9 xo 10, 1,11 ECE4680 Haza Daa Haza o 1: (Fig. 6.36, pag 477) Dpci backwa i im a haza. Tim (clock cycl) F D/RF EX MEM WB a 1,2,3 ub 4,1,3 a 6,1,7 o 8,1,9 xo 10,1,11 m Rg Dm Rg Shaig o igh/lf half ma a/wi o ha lm. ECE4680 Haza

9 pio1: HW Sall o Rolv Daa Haza Dpci backwa i im a haza. Tim (clock cycl) F D/RF EX MEM WB a 1,2,3 ub 4, 1,3 a 6,1,7 o 8,1,9 xo 10,1,11 m bubbl bubbl bubbl Rg Dm Rg m Rg Dm m Rg m Rg Th Cool logic ca b complx ECE4680 Haza Bu call u of Daa Saioay Cool Th Mai Cool ga h cool igal uig Rg/Dc Cool igal fo Exc (Exp, Sc,...) a u 1 cycl la Cool igal fo Mm (MmW Bach) a u 2 cycl la Cool igal fo W (MmoRg MmW) a u 3 cycl la Rg/Dc Exc Mm W Exp Exp Sc Sc F/D Rgi Mai Cool p RgD MmW Bach MmoRg D/Ex Rgi p RgD MmW Bach MmoRg Ex/Mm Rgi MmW Bach MmoRg Mm/W Rgi MmoRg RgW RgW RgW RgW ECE4680 Haza

10 pio 1: How HW ally all pipli. HW o chag PC kp fchig am iucio & cool igal o big valu (0) Tim (clock cycl) F D/RF EX MEM WB a 1,2,3 all all all ub 4,1,3 m bubbl bubbl bubbl bubbl m bubbl bubbl bubbl bubbl m bubbl bubbl bubbl bubbl a 6,1,7 m Rg Dm ECE4680 Haza pio 2: SW i ip iucio Wo ca i NP iucio. Tim (clock cycl) F D/RF EX MEM WB a 1,2,3 op op op ub 4,1,3 m Rg Dm Rg a 6,1,7 m Rg Dm ECE4680 Haza

11 pio 3 igh: Daa i availabl! (Fig. 6.37, pag 481) Pipli gi alay coai aa. Tim (clock cycl) F D/RF EX MEM WB a 1,2,3 ub 4,1,3 a 6,1,7 o 8,1,9 xo 10,1,11 m Rg Dm Rg ECE4680 Haza HW Chag fo Fowaig (Bypaig):(Fig , p ) ca muliplxo o a pah fom pipli gi Aum gi a uig wi g w valu (ohwi mo ul o b fowa) D/EX EX/MEM MEM/WB M u x M u x Zo? Daa Mmoy ECE4680 Haza

12 Clock Fom La Lcu: Th Dlay Loa Phomo Cycl 1 Cycl 2 Cycl 3 Cycl 4 Cycl 5 Cycl 6 Cycl 7 Cycl 8 0: Loa fch Rg/Dc Exc Mm W Plu 1 fch Rg/Dc Exc Mm W Plu 2 fch Rg/Dc Exc Mm W Plu 3 fch Rg/Dc Exc Mm W Plu 4 fch Rg/Dc Exc Mm W Alhough Loa i fch uig Cycl 1: Th aa i NT wi io h Rg Fil uil h of Cycl 5 W cao a hi valu fom h Rg Fil uil Cycl 6 3-iucio lay bfo h loa ak ffc ECE4680 Haza Fowaig uc Daa Haza o 1 cycl: (Fig. 6.44, p489). Tim (clock cycl) F D/RF EX MEM WB lw 1, 0(2) ub 4,1,6 a 6,1,7 o 8,1,9 m Rg Dm Rg ECE4680 Haza

13 pio1: HW Sall o Rolv Daa Haza lock : chck fo haza & all. Tim (clock cycl) F D/RF EX MEM WB lw 1, 0(2) all ub 4,1,3 a 6,1,7 o 8,1,9 m bubbl bubbl bubbl bubbl m Rg Dm Rg ECE4680 Haza pio 2: SW i ip iucio. Wo ca i NP iucio MPS oluio: No HW chckig Tim (clock cycl) F D/RF EX MEM WB lw 1, 0(2) op ub 4,1,3 a 6,1,7 o 8,1,9 m Rg Dm Rg ECE4680 Haza

14 Sofwa Schulig o Avoi Loa Haza Ty poucig fa co fo a = b + c; = f; aumig a, b, c,,, a f i mmoy. Slow co: LW Rb,b LW Rc,c ADD Ra,Rb,Rc SW a,ra LW R, LW Rf,f SUB R,R,Rf SW,R Fa co: LW LW LW ADD LW SW SUB SW Rb,b Rc,c R, Ra,Rb,Rc Rf,f a,ra R,R,Rf,R ECE4680 Haza Compil Avoiig Loa Sall: chul uchul gcc pic x 14% 25% 31% 42% 54% 65% 0% 20% 40% 60% 80% % loa allig pipli ECE4680 Haza

15 Fom La Lcu: Th Dlay Bach Phomo Cycl 4 Cycl 5 Cycl 6 Cycl 7 Cycl 8 Cycl 9 Cycl 10 Cycl 11 Clk 12: Bq fch Rg/Dc Exc Mm W (ag i 1000) 16: R-yp fch Rg/Dc Exc Mm W 20: R-yp fch Rg/Dc Exc Mm W 24: R-yp fch Rg/Dc Exc Mm W 1000: Tag of B fch Rg/Dc Exc Mm W Alhough Bq i fch uig Cycl 4: Tag a i NT wi io h PC uil h of Cycl 7 Bach ag i NT fch uil Cycl 8 3-iucio lay bfo h bach ak ffc ECE4680 Haza Cool Haza o Bach: 3 ag all (Fig. 6.50, P497) Tim (i Clock Cycl) CC 1 CC 2 CC 3 CC 4 CC 5 CC 6 CC 7 CC 8 CC 9 Pogam Excuio (i ucio) 40 bq $1,$3,36 $3, a $12,$2,$5 $2, $5 48 o o $13,$6,$2 $6, $2 M Rg M Rg M DM Rg Rg DM Rg DM Rg 52 a $14,$2,$2 $2, $2 M Rg DM Rg l lw $4,$7,100 50($7) M Rg DM Rg ECE4680 Haza

16 Bach Sall mpac Why? f CP = 1, 30% bach, Sall 3 cycl w CP = 1.9! 2 pa oluio: Dmi bach ak o o oo, AND Compu ak bach a ali MPS bach = 0 o 0 Soluio pio 1: Mov Zo o D/RF ag A o calcula w PC i D/RF ag 1 clock cycl paly fo bach v. 3 ECE4680 Haza pio 1: mov HW fowa o uc bach lay ucio Fch. Dco Rg. Fch Excu A. Calc. Mmoy Acc Wi Back F/D D/EX EX/MEM M u x MEM/WB ADD 4 Zo? R PC ucio Mmoy R R MEM/WB.R Rgi M u x M u x Daa Mmoy M u x Sig x ECE4680 Haza

17 Bach Dlay ow 1 clock cycl ucio Fch. Dco Rg. Fch Excu A. Calc. Mmoy Acc Wi Back F/D M u x D/EX EX/MEM MEM/WB ADD Zo? ADD 4 R PC ucio Mmoy R R MEM/WB.R Rgi M u x M u x Daa Mmoy M u x Sig x ECE4680 Haza pio 2: Dfi Bach a Dlay Wo ca, Sofwa i NP io bach lay Wh o g iucio o fill bach lay lo? Bfo bach iucio Fom h ag a: oly valuabl wh bach Fom fall hough: oly valuabl wh o bach Compil ffciv fo igl bach lay lo: Fill abou 60% of bach lay lo Abou 80% of iucio xcu i bach lay lo uful i compuaio abou 50% (60% x 80%) of lo ufully fill ECE4680 Haza

18 Wh i pipliig ha? (1) up: 5 iucio xcuig i 5 ag pipli How o op h pipli? Ra? Who cau h iup? Sag Poblm iup occuig F Pag faul o iucio fch; mialig mmoy acc; mmoy-pocio violaio D Ufi o illgal opco EX Aihmic iup MEM Pag faul o aa fch; mialig mmoy acc; mmoy-pocio violaio Loa wih aa pag faul, A wih iucio pag faul? Soluio 1: iup vco/iucio 2: iup ASAP, a vyhig icompl ECE4680 Haza Wh i pipliig ha? (2) Complx Aig Mo a ucio A mo: Auo icm cau gi chag uig iucio xcuio up? Now woy abou wi haza ic wi o log la ag - Wi Af Ra (WAR): Wi occu bfo ip a - Wi Af Wi (WAW): Wi occu i wog o, lavig wog ul i gi - (Pviou aa haza call RAW, fo Ra Af Wi) Mmoy-mmoy Mov iucio Mulipl pag faul mak pog? ECE4680 Haza

19 Wh i pipliig ha? (3) Floaig Poi: log xcuio im Alo, may pipli FP xcuio ui o ha ca iiia w iucio wihou waiig full lacy FP ucio Lacy iiaio Ra (MPS R4000) A, Subac 4 3 Muliply 8 4 Divi Squa oo Nga 2 1 Abolu valu 2 1 FP compa 3 2 Divi, Squa Roo ak -10X o -30X log ha A Excpio? A WAR a WAW haza ic pipli a o log am lgh ECE4680 Haza Daa Haza Ra Af Wi (RAW) Ampig o a a valu ha ha' b wi y. Thi i h mo commo yp, a ca b ovcom by fowaig. Wi af wi (WAW): Wiig a valu bfo a pcig wi ha compl. Thi ca oly happ i complx pip ha allow iucio o poc ou of o, o ha hav mulipl wi-back ag (moly CSC), o ha hav mulipl pip ha ca wi. Wi af a (WAR): Wiig a valu bfo a pcig a ha compl. Th alo qui a complx pipli ha ca omim wi i a aly ag, a a i a la ag. i alo poibl wh mulipl pipli o ou-of-o iu a mploy. Ra af a (RAR) o o pouc a haza. ECE4680 Haza

20 Haza Dcio Suppo iucio i i abou o b iu a a pco iucio j i i h iucio pipli. Rg ( i ) = Rgi a by iucio i Wg ( i ) = Rgi wi by iucio i A RAW haza xi o gi ρ if ρ, ρ Rg( i ) Wg( j ) Kp a co of pig wi (fo i' i h pip) a compa wih opa g of cu iucio. Wh iucio iu, v i ul gi. Wh o opaio compl, mov i wi vaio. A WAW haza xi o gi ρ if ρ, ρ Wg( i ) Wg( j ) A WAR haza xi o gi ρ if ρ, ρ Wg( i ) Rg( j ) ECE4680 Haza Avoiig Daa Haza by Dig Suppo iucio a xcu i a pipli fahio uch ha ucio a iiia i o. WAW avoiac: if wi o a paicula ouc (.g., g) a pfom i h am ag fo all iucio, h o WAW haza occu. poof: wi a i h am im quc a iucio. R/D E W R/D E W R/D E W WAR avoiac: if i all iucio a of a ouc occu a a ali ag ha wi o ha ouc occu i ay iucio, h o WAR haza occu. poof: A ucco iucio mu iu la, hc i will pfom wi oly af all a fo h cu iucio. ECE4680 Haza

21 Fi Gaio RSC Pipli All iucio follow am pipli o ( aic chul ). Rgi wi i la ag Avoi WAW haza All gi a pfom i fi ag af iu. Avoi WAR haza Mmoy acc i ag 4 Avoi all mmoy haza Cool haza olv by lay bach (wih fa pah) RAW haza olv by bypa, xcp o loa ul which a olv by fia (lay loa). Subaial pipliig wih vy lil co o complxiy. Machi ogaizaio i (lighly) xpo! Rli vy havily o "hi aumpio"of mmoy acc i cach ECE4680 Haza Rviw: Summay of Pipliig Baic Sp Up Š Pipli Dph; if ial CP i 1, h: Spup = Pipli ph 1+Pipli all cycl p iucio Clock cycl upipli Clock cycl pipli Haza limi pfomac o compu: ucual: mo HW ouc aa: fowaig, compil chulig cool: aly valuaio & PC, lay bach, picio caig lgh of pip ica impac of haza ic pipliig hlp iucio bawih, o lacy Compil ky o ucig co of aa a cool haza loa lay lo bach lay lo Excpio, ucio S, FP mak pipliig ha Log pipli => Bach picio, mo iucio paalllim? ECE4680 Haza