IP Lookup-2: The Completion Buffer. IP-Lookup module without the completion buffer

Transcription

1 P Lkup-2: The Cmpletn Buffer Arvnd Cmputer Scence & Artfcal ntellgence Lab Massachusetts nsttute f Technlgy February 24, L07-1 P-Lkup mdule wthut the cmpletn fer enter RAM ff dne? utq ge etresult mdule mkplkup(plkup); rule recrculate ; rule ext ; methd Actn enter (P p); ram.req(p[31:16]); ff.enq(p[15:0]); methd Actnalue#(Msg) getresult(); utq.deq(); return utq.frst(); endmdule L07-2 1

2 P Lkup rules rule recrculate (!sleaf(ram.peek())); P rp = ff.frst(); ff.enq(rp << 8); ram.req(ram.peek() + rp[15:8]); ff.deq(); ram.deq(); rule ext (sleaf(ram.peek())); utq.enq(ram.peek()); ff.deq(); ram.deq(); Methd enter and rule ext can be scheduled smultaneusly, assumng ff.enq and ff.deq can be dne smultaneuslyand ram.req and ram.deq can be dne smultaneusly L07-3 P-Lkup mdule wth the cmpletn fer enter gettken yes RAM dne? n ff utq c ge etresult The packets may cme ut f rder Cmpletn fer ensures that departures take place n rder even f lkups cmplete ut-f-rder Snce c has fnte capacty t gves ut tkens t cntrl the entry nt the crcular ppelne The ff nw must als hld the tken whle the memry access s n prgress: Tuple2#(Tken,Bt#(16)) remanngp L07-4 2

3 Cmpletn fer: nterface gettken c getresult put (result & tken) nterface CBuffer#(type t); methd Actnalue#(Tken) gettken(); methd Actn put(tken tk, t d); methd Actnalue#(t) getresult(); endnterface typedef Bt#(TLg#(n)) TkenN#(numerc type n); typedef TkenN#(16) Tken; L07-5 P-Lkup mdule wth the cmpletn fer gettken e nter RAM ff dne? yes mdule mkplkup(plkup); rule recrculate ; rule ext ; methd Actn enter (P p); Tken tk <- c.gettken(); ram.req(p[31:16]); req(p[31:16]); ff.enq(tuple2(tk,p[15:0])); methd Actnalue#(Msg) getresult(); let result <- c.getresult(); return result; endmdule n c get tresult fr enter and getresult t execute smultaneusly, c.gettken and c.getresult must execute smultaneusly February 24, 2010 L07-6 3

4 P Lkup rules wth cmpletn fer rule recrculate (!sleaf(ram.peek())); match{.tk,.rp} = ff.frst(); ff.enq(tuple2(tk,(rp << 8))); ram.req(ram.peek() + rp[15:8]); ff.deq(); ram.deq(); rule ext (sleaf(ram.peek())); c.put(ram.peek()); ff.deq(); ram.deq(); Fr rule ext and methd enter t execute smultaneusly, c.put and c.gettken must execute smultaneusly February 24, 2010 Fr n dead cycles c.gettken and c.put and c.getresult must be able t execute smultaneusly L07-7 Cmpletn fer: mplementatn A crcular fer wth tw pnters and, and a cunter cnt Elements are f Maybe type mdule mkcbuffer (CBuffer#(t)) prvss (Bts#(t,sz)); RegFle#(Tken, Maybe#(t)) <- mkregflefull(); Reg#(Tken) <- mkreg(0); //nput ndex cnt Reg#(Tken) <- mkreg(0); //utput ndex Reg#(nt#(32)) cnt <- mkreg(0); //number f flled slts Elements must be representable as bts L07-8 4

5 Cmpletn fer: Cncurrency ssue cnt // state elements //,,, cnt... methd Actnalue#(t) gettken() f (cnt < maxtken); cnt <= cnt + 1; <= (==maxtken)? 0 : + 1;.upd(, nvald); return ; methd Actn put(tken tk, t data); Can these methds execute cncurrently? NO!.upd(tk, ald data); methd Actnalue#(t) getresult() f (cnt > 0) &&& (.sub() matches tagged (ald.x)); <= (==maxtken)? 0 : + 1; cnt <= cnt - 1; return x; L07-9 Cncurrency Analyss Prblem 1 A crcular fer wth tw pnters and, and a cunter cnt Elements are f Maybe type cnt must allw tw smultaneus updates and ne read Needs a regster fle wth ne read and tw wrte prts Snce the updates are always t dfferent addresses there s n data hazard and cncurrent peratns shuld be permtted L07-10 N cmpler can detect that wthut full prgram analyss (.e., understandng the use pattern) 5

6 Cncurrency Analyss Prblem -2 // state elements //,,, cnt... methd Actnalue#(t) gettken() f (cnt < maxtken); cnt cnt <= cnt + 1; <= (==maxtken)? 0 : + 1;.upd(, nvald); return ; methd Actn put(tken tk, t data); Cncurrent updates t cnt.upd(tk, ald data); methd Actnalue#(t) getresult() f (cnt > 0) &&& (.sub() matches tagged (ald.x)); <= (==maxtken)? 0 : + 1; cnt <= cnt - 1; return x; L07-11 A specal cunter mdule We ften need t keep cunt f certan events Need t read cunt, decrement and ncrement Snce decrementng and ncrementng dn t change the cunt we can remve sme bypassng lnks mplemented as Cunter Lbrary mdules (mplemented usng Rwres) L

7 Cunter mdule mdule mkcunter#(t v) (Cunter#(t)) prvss(arth#(t), Lteral#(t)); Reg#(t) cnt <- mkcnfgreg(v); RWre#(t) up <- mkrwre(); RWre#(t) dn <- mkrwre(); Cautn: rule update (*fre_when_enabled*) must fre therwse the rule update(true); cnt wn t be updated cnt <= cnt + frmmaybe(0, up.wget) - frmmaybe(0, dn.wget); methd t _read() = cnt; methd Actn ncr(x) = up.wset(x); methd Actn decr(x) = dn.wset(x); endmdule L07-13 Multprted Regster fle 1R and 1W prts bypass r n bypass 2R and 1W prts bypass r n bypass 1R and 2W prts All useful and each requres a dfferent mplementatn multple wrtes nt the same regster? Whch type f RF errr vs prrty d we need fr the bypass r n bypass cmpletn fer? L

8 Cmpletn fer: Regster Fle cnt // state elements, // cnt <- mkcunter(0); <-? methd Actnalue#(t) gettken() f (cnt.read() < maxtken); cnt.ncr(); <= (==maxtken)? 0 : + 1; [] <= nvald; return ; methd Actn put(tken tk, t data); [tk] <= ald data; shuld have 2W and 1R prts - multple wrte errr - n bypassng methd Actnalue#(t) getresult() f (cnt.read() > 0) &&& ([] matches tagged ald.x); <= (==maxtken)? 0 : + 1; cnt.decr(); return x; L R and 2W Regster fle multple wrtes errr; n bypassng mdule mkregflefull1r1r2w(regfle2#(addr,alue)); Reg#(ectr#(AddrSz, alue)) vs <- mkregu; RWre#(Tuple2#(Addr, alue)) w1 <- mkrwre; RWre#(Tuple2#(Addr, alue)) w2 <- mkrwre; (* fre_when_enabed *) rule update(true); let vs_new = vs; case w1.wget() matches tagged ald {.1,.v1}: vs_new[1]=v1; endcase case w2.wget() wget() matches tagged ald {.2,.v2}: vs_new[2]=v2; endcase vs <= vs_new; methd read() = vs[]; methd w1(,v) = w1.wset(tuple2(,v)); methd w2(,v) = w2.wset(tuple2(,v)); endmdule L

9 Cmpletn fer cnt // state elements, // cnt <- mkcunter(0); // <- mkregfle1r2w; methd Actnalue#(t) gettken() f (cnt.read() < maxtken); cnt.ncr(); <= (==maxtken)? 0 : + 1;.w1(,nvald); return ; Prblem slved methd Actn put(tken tk, t data);.w2(tk, ald data); methd Actnalue#(t) getresult() f (cnt.read() > 0) &&& (.read matches tagged ald.x); <= (==maxtken)? 0 : + 1; cnt.decr(); return x; L07-17 Lngest Prefx Match fr P lkup: 3 pssble mplementatn archtectures Rgd ppelne Lnear ppelne Crcular ppelne neffcent memry usage but smple desgn Effcent memry usage thrugh memry prt replcatr Effcent memry wth mst cmplex cntrl February 24, Whch s best? Arvnd, Nkhl, Rsenband & Dave CCAD 2004 L

10 mplementatns f Statc ppelnes Tw desgners, tw results LPM versns Best Area (gates) Statc (Replcated FSMs) Statc (Sngle FSM) Best Speed (ns) Replcated: P addr result MUX / De-MUX BEST: P addr MUX result Each packet s prcessed by ne FSM FSM Cunter FSM FSM FSM MUX / De-MUX February 24, RAM FSM RAM Shared FSM L07-19 Synthess results LPM versns Cde sze (lnes) Best Area (gates) Best Speed (ns) Mem. utl. (randm wrklad) Statc % Statc BS (5% larger) 3.32 (7% faster) 63.5% Lnear % Lnear BS (8% larger) 4.7 (same) 99.9% Crcular % Crcular BS (1% larger) 3.67 (2% slwer) 99.9% Synthess: TSMC 0.18 µm lb - Bluespec results can match carefully cded erlg - Mcr-archtecture has a dramatc mpact n perfrmance - Archtecture dfferences are much mre mprtant than language dfferences n determnng QR February 24, 2010 = erlg;bs = Bluespec System erlg L