CS 61C: Great Ideas in Computer Architecture (Machine Structures) Instruc(on Level Parallelism: Mul(ple Instruc(on Issue

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CS 61C: Gat Ida in Comput Achitctu (Machin Stuctu) Intuc(on Lvl Paalllim: Mul(pl Intuc(on Iu Intucto: Randy H. Katz David A. PaGon hgp://int.c.bkly.du/~c61c/fa10 1 Paalll Rqut Aignd to comput.g., Sach Katz Paalll Thad Aignd to co.

1 CS 61C: Gat Ida in Comput Achitctu (Machin Stuctu) Intuc(on Lvl Paalllim: Mul(pl Intuc(on Iu Intucto: Randy H. Katz David A. PaGon hgp://int.c.bkly.du/~c61c/fa10 1 Paalll Rqut Aignd to comput.g., Sach Katz Paalll Thad Aignd to co.g., Lookup, Ad So7wa Paalll IntucZon >1 on Zm.g., 5 piplind intuczon Paalll Data >1 data on Zm.g., Add of 4 pai of wod Hadwa dcipzon All gat funczoning in paalll at am Zm You A H! Han Paalllim & Achiv High Pfomanc Hadwa Today Lctu Wahou Scal Comput Co Mmoy Input/utput IntucZon Unit() Main Mmoy Co Smat Phon Logic Gat 3 Comput (Cach) Co FuncZonal Unit() A 0 +B 0 A 1 +B 1 A 2 +B 2 A 3 +B 3 Rviw: Hazad SituaZon that pvnt tazng th nxt logical intuczon in th nxt clock cycl 1. Stuctual hazad Rquid ouc i buy (.g., ad/wit g fil at am Zm) 2. Data hazad Nd to wait fo pviou intuczon to complt it data ad/wit (.g., pviou intuczon han t wign back a ult ndd by cunt intuczon) 3. Contol hazad Dciding on contol aczon dpnd on pviou intuczon (.g., whth o not banch wa takn) Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay 4 5 Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay 3. Contol Hazad Banch dtmin flow of contol Ftching nxt intuczon dpnd on banch outcom Piplin can t alway ftch coct intuczon SZll woking on ID tag of banch BEQ, BNE in MIPS piplin Simpl oluzon pzon 1: Stall on vy banch unzl hav nw PC valu Would add 2 bubbl/clock cycl fo vy Banch! (~ 20% of intuczon xcutd) 4/7/11 6 Sping Lctu #21 7 1

in Stag 2, only on unncay intuczon i ftchd, o only on no- op i ndd Sid Not: man that banch a idl in Stag 3, 4 and 5 9 Coctd Datapath fo BEQ/BNE? n Clock Cycl Stall Tim (clock cycl) I n t.

2 I n t. d bq Int 1 Int 2 Int 3 Int 4 Stall => 2 Bubbl/Clock Tim (clock cycl) I$ Wh do w do th compa fo th banch? Rg D$ Rg 8 3. Contol Hazad: Banching pzmizazon #1: Int pcial banch compaato in Stag 2 A oon a intuczon i dcodd (pcod idnzfi it a a banch), immdiatly mak a dciion and t th nw valu of th PC Bnfit: inc banch i complt in Stag 2, only on unncay intuczon i ftchd, o only on no- op i ndd Sid Not: man that banch a idl in Stag 3, 4 and 5 9 Coctd Datapath fo BEQ/BNE? n Clock Cycl Stall Tim (clock cycl) I n t. d bq Int 1 Int 2 Int 3 Int 4 I$ Rg D$ Rg 10 Studnt RoulG? Banch compaato movd to Dcod tag Contol Hazad 3. Contol Hazad: Banching pzon 2: Pdict outcom of a banch, fix up if gu wong Mut cancl all intuczon in piplin that dpndd on a wong gu Simplt hadwa if w pdict that all banch a NT takn Why? pzon #3: Rdfin banch ld dfinizon: if w tak th banch, non of th intuczon a th banch gt xcutd by accidnt Nw dfinizon: whth o not w tak th banch, th ingl intuczon immdiatly following th banch gt xcutd (th banch- dlay lot) Dlayd Banch man w alway xcut int a7 banch Thi opzmizazon i ud with MIPS 12 Studnt RoulG? 13 2

3 3. Contol Hazad: Banching Not on Banch- Dlay Slot Wot- Ca Scnaio: put a no- op in th banch- dlay lot BG Ca: plac om intuczon pcding th banch in th banch- dlay lot a long a th changd don t affct th logic of pogam R- oding intuczon i common way to pd up pogam Compil uually find uch an intuczon 50% of Zm Jump alo hav a dlay lot 14 Exampl: Nondlayd v. Dlayd Banch Nondlayd Banch Dlayd Banch o $8, $9, $10 add $1, $2,$3 add $1, $2, $3 ub $4, $5, $6 ub $4, $5, $6 bq $1, $4, Exit bq $1, $4, Exit o $8, $9, $10 xo $10, $1, $11 xo $10, $1, $11 Exit: Exit: 15 Dlayd Banch/Jump and MIPS ISA? Why do JAL put PC+8 in git 31? Dlayd Banch/Jump and MIPS ISA? Why do JAL put PC+8 in git 31? JAL xcut following intuc(on (PC+4) o hould tun to PC+8 16 Studnt RoulG? 17 Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay Adminitivia Pojct 4: 2 Stag Piplind Cycl Poco, non- dlayd banch, in Logiim Pat 1, Datapath, du 4/10, Pat 2 du 4/17 Fac- to- Fac gading: Signup fo Zmlot lat wk Exta Cdit: Fatt Vion of Pojct 3 Du 4/24 23:59:59 Final Rviw: 5/2, 5-8 PM, 2050 Vally LSB Final: Mon May 9 11AM- 2PM (TBD)

4 Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay Gat IntucZon- Lvl Paalllim (ILP) Dp piplin (5 => 10 => 15 tag) L wok p tag hot clock cycl MulZpl iu upcala Rplicat piplin tag mulzpl piplin Stat mulzpl intuczon p clock cycl CPI < 1, o u IntucZon P Cycl (IPC) E.g., 4 GHz 4- way mulzpl- iu 16 BIPS, pak CPI = 0.25, pak IPC = 4 But dpndnci duc thi in paczc 4.10 Paalllim and Advancd IntucZon Lvl Paalllim 4/7/11 21 Sping Lctu #21 22 MulZpl Iu StaZc mulzpl iu Compil goup intuczon to b iud togth Packag thm into iu lot Compil dtct and avoid hazad Dynamic mulzpl iu CPU xamin intuczon tam and choo intuczon to iu ach cycl Compil can hlp by oding intuczon CPU olv hazad uing advancd tchniqu at unzm Supcala Laundy: Paalll p tag T a k 6 PM AM A B C Tim (light clothing) (dak clothing) (vy dity clothing) D (light clothing) d E (dak clothing) F (vy dity clothing) Mo ouc, HW to match mix of paalll tak? Piplin Dpth and Iu Width Intl Poco ov Tim Micopoco Ya Clock Rat Piplin Stag Iu width Co Pow i MHz W Pntium MHz W Pntium Po MHz W P4 Willamtt MHz W P4 Pcott MHz W Co 2 Cono MHz W Co 2 Yokfild MHz W Co i7 Gulftown MHz W Piplin Dpth and Iu Width Clock 1000 Pow 100 Piplin Stag Iu width 10 Co

5 StaZc MulZpl Iu Compil goup intuczon into iu packt Goup of intuczon that can b iud on a ingl cycl Dtmind by piplin ouc quid Think of an iu packt a a vy long intuc(on Spcifi mulzpl concunt opazon Schduling StaZc MulZpl Iu Compil mut mov om/all hazad Rod intuczon into iu packt No dpndnci within a packt Poibly om dpndnci btwn packt Vai btwn ISA; compil mut know! Pad with nop if ncay MIPS with StaZc Dual Iu Dual- iu packt n /banch intuczon n load/to intuczon 64- bit alignd /banch, thn load/to Pad an unud intuczon with nop Add Intuction typ Piplin Stag n /banch IF ID EX MEM WB n + 4 Load/to IF ID EX MEM WB n + 8 /banch IF ID EX MEM WB n + 12 Load/to IF ID EX MEM WB n + 16 /banch IF ID EX MEM WB n + 20 Load/to IF ID EX MEM WB Hazad in th Dual- Iu MIPS Mo intuczon xcuzng in paalll EX data hazad Fowading avoidd tall with ingl- iu piplin Now can t u ult in load/to in am packt add $t0, $0, $1 load $2, 0($t0) Split into two packt, ffczvly a tall Load- u hazad SZll on cycl u latncy, but now two intuczon Mo aggiv chduling quid Schduling Exampl Schdul thi fo dual- iu MIPS Loop: lw $t0, 0($1) # $t0=aay lmnt addu $t0, $t0, $2 # add cala in $2 w $t0, 0($1) # to ult addi $1, $1, 4 # dcmnt point bn $1, $zo, Loop # banch $1!=0 /banch Load/to cycl Loop: nop lw $t0, 0($1) 1 addi $1, $1, 4 nop 2 addu $t0, $t0, $2 nop 3 bn $1, $zo, Loop w $t0, 4($1) 4 IPC = 5/4 = 1.25 (c.f. pak IPC = 2) Loop Unolling Rplicat loop body to xpo mo paalllim Rduc loop- contol ovhad U diffnt git p plicazon Calld git naming Avoid loop- caid an(- dpndnci Sto followd by a load of th am git Aka nam dpndnc Ru of a git nam

6 Loop Unolling Exampl /banch Load/to cycl Loop: addi $1, $1, 16 lw $t0, 0($1) 1 nop lw $t1, 12($1) 2 addu $t0, $t0, $2 lw $t2, 8($1) 3 addu $t1, $t1, $2 lw $t3, 4($1) 4 addu $t2, $t2, $2 w $t0, 16($1) 5 addu $t3, $t4, $2 w $t1, 12($1) 6 nop w $t2, 8($1) 7 bn $1, $zo, Loop w $t3, 4($1) 8 IPC = 14/8 = 1.75 Clo to 2, but at cot of git and cod iz Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay Dynamic MulZpl Iu Supcala poco CPU dcid whth to iu 0, 1, 2, intuczon ach cycl Avoiding tuctual and data hazad Avoid nd fo compil chduling Though it may Zll hlp Cod manzc nud by th CPU Dynamic Piplin Schduling Allow th CPU to xcut intuczon out of od to avoid tall But commit ult to git in od Exampl lw $t0, 20($2) addu $t1, $t0, $t2 ubu $4, $4, $t3 lti $t5, $4, 20 Can tat ubu whil addu i waizng fo lw Why Do Dynamic Schduling? Why not jut lt th compil chdul cod? Not all tall a pdicabl.g., cach mi Can t alway chdul aound banch Banch outcom i dynamically dtmind Diffnt implmntazon of an ISA hav diffnt latnci and hazad SpculaZon Gu what to do with an intuczon Stat opazon a oon a poibl Chck whth gu wa ight If o, complt th opazon If not, oll- back and do th ight thing Common to tazc and dynamic mulzpl iu Exampl Spculat on banch outcom (Banch PdicZon) Roll back if path takn i diffnt Spculat on load Roll back if locazon i updatd

T a k d Piplin Hazad: Matching ock in lat load 6 PM 7 8 9 10 11 12 1 2 AM A B C D E F 30 30 30 30 30 30 30 bubbl A dpnd on D; tall inc fold Zd up; Tim 39 ut- of- d Laundy: Don t Wait 6 PM 7 8 9 10 11

Ftch intuczon in pogam od ( 4/clock) 2. Pdict banch a takn/untakn 3. To avoid hazad on git, nam git uing a t of intnal git (~80 git) 4.

7 T a k d Piplin Hazad: Matching ock in lat load 6 PM AM A B C D E F bubbl A dpnd on D; tall inc fold Zd up; Tim 39 ut- of- d Laundy: Don t Wait 6 PM AM T Tim a k A B C bubbl d D E F A dpnd on D; t conznu; nd mo ouc to allow out- of- od 40 ut- of- d ExcuZon (1/2) Baically, unoll loop in hadwa 1. Ftch intuczon in pogam od ( 4/clock) 2. Pdict banch a takn/untakn 3. To avoid hazad on git, nam git uing a t of intnal git (~80 git) 4. CollcZon of namd intuczon might xcut in a window (~60 intuczon) 5. Excut intuczon with ady opand in 1 of mulzpl func(onal unit (, FPU, Ld/St) 41 ut- of- d ExcuZon (2/2) Baically, unoll loop in hadwa 6. Buff ult of xcutd intuczon unzl pdictd banch a olvd in od buff 7. If pdictd banch coctly, commit ult in pogam od 8. If pdictd banch incoctly, dicad all dpndnt ult and tat with coct PC 42 Dynamically Schduld CPU Pv dpndnci ut f d Intl All u inc 2001 Rod buff fo git wit Can upply opand fo iud intuczon Hold pnding opand Rult alo nt to any waizng vazon tazon Micopoco Ya Clock Rat Piplin Stag 43 Iu width ut-of-od/ Spculation Co i MHz 5 1 No 1 5W Pow Pntium MHz 5 2 No 1 10W Pntium Po MHz 10 3 Y 1 29W P4 Willamtt MHz 22 3 Y 1 75W P4 Pcott MHz 31 3 Y 1 103W Co MHz 14 4 Y 2 75W Co 2 Yokfild MHz 16 4 Y 4 95W Co i7 Gulftown MHz 16 4 Y 6 130W 44 7

Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay Contol

tag) Up to 106 RISC- op in pog Intl Nhalm i 16 tag fo intg opazon, dtail not vald, but likly imila to abov+ Intl

Th BIG Pictu Y, but not a much a w d lik Poga

8 Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay Contol Hazad Adminitivia High Lvl ILP Tchnology Bak Exampl AMD Baclona Big Pictu: Typ of Paalllim Summay AMD pton X4 Micoachitctu 72 phyical git 4.11 Ral Stuff: Th AMD pton X4 (Baclona) Piplin AMD pton X4 Piplin Flow Fo intg opazon 12 tag (FloaZng Point i 17 tag) Up to 106 RISC- op in pog Intl Nhalm i 16 tag fo intg opazon, dtail not vald, but likly imila to abov+ Intl call RISC opazon Mico opazon o μop Do MulZpl Iu Wok? Th BIG Pictu Y, but not a much a w d lik Pogam hav al dpndnci that limit ILP Som dpndnci a had to liminat.g., point aliaing Som paalllim i had to xpo Limitd window iz duing intuczon iu Mmoy dlay and limitd bandwidth Had to kp piplin full SpculaZon can hlp if don wll High Lvl ILP Adminitivia Exampl AMD Baclona Tchnology Bak Big Pictu: Typ of Paalllim Summay

9 Nw- School Machin Stuctu Paalll Rqut Aignd to comput.g., Sach Katz Paalll Thad Aignd to co.g., Lookup, Ad So7wa Paalll IntucZon >1 on Zm.g., 5 piplind intuczon Paalll Data >1 data on Zm.g., Add of 4 pai of wod Hadwa dcipzon All gat funczoning in paalll at am Zm Han Paalllim & Achiv High Pfomanc Hadwa Wahou Scal Comput Pojct 2 Co Mmoy Input/utput IntucZon Unit() Main Mmoy Co Smat Phon Logic Gat Pojct 52 4 Comput (Cach) Co FuncZonal Unit() A 0 +B 0 A 1 +B 1 A 2 +B 2 A 3 +B 3 Pojct 1 Pojct 3 Big Pictu on Paalllim Two typ of paalllim in applica(on 1. Data- Lvl Paalllim (DLP): ai bcau th a many data itm that can b opatd on at th am Zm 2. Tak- Lvl Paalllim (TLP): ai bcau tak of wok a catd that can opat lagly in paalll 53 Big Pictu on Paalllim Hadwa can xploit app Data LP and Tak LP in 4 way: 1. Intuc(on- Lvl Paalllim: Hadwa xploit applicazon DLP uing ida lik piplining and pculazv xcuzon 2. SIMD achitctu: xploit app DLP by applying a ingl intuczon to a collczon of data in paalll 3. Thad- Lvl Paalllim: xploit ith app DLP o TLP in a Zghtly- coupld hadwa modl that allow fo intaczon among paalll thad 4. Rqut- Lvl Paalllim: xploit paalllim among lagly dcoupld tak and i pcifid by th pogamm of th opazng ytm And in Concluion, Big Ida of IntucZon Lvl Paalllim Piplining, Hazad, and Stall Fowading, SpculaZon to ovcom Hazad MulZpl iu to inca pfomanc IPC intad of CPI Dynamic ExcuZon: Supcala in- od iu, banch pdiczon, git naming, out- of- od xcuzon, in- od commit unoll loop in HW, hid cach mi

P&H 4.51 Pipelined Control. 3. Control Hazards. Hazards. Stall => 2 Bubbles/Clocks Time (clock cycles) Control Hazard: Branching 4/15/14

P&H 4.51 Pipelined Control. 3. Control Hazards. Hazards. Stall => 2 Bubbles/Clocks Time (clock cycles) Control Hazard: Branching 4/15/14 P&H.51 Piplind Contol CS 61C: Gat Ida in Comput Achitctu (Machin Stuctu) Lctu 2: Piplin Paalllim Intucto: Dan Gacia int.c.bkly.du/~c61c! Hazad SituaHon that pvnt tahng th nxt logical intuchon in th nxt