[_CD4_]<dragon>Dragoman>CacheModelImpl.mesa!1

CacheModelImpl.mesa

Russ Atkinson, September 19, 1984 4:15:08 pm PDT

Last Edited by: Sweet, March 19, 1985 10:14:53 am PST

DIRECTORY

Basics USING [BITSHIFT],

DragOpsCross USING [Half, Word, ZerosWord],

DragOpsCrossUtils USING [AddDelta, HalfShift, HalfToCard, HalfXor, LowHalf, WordToHalves],

CacheModel USING

[CacheBase, CacheBaseRep, CacheFetchProc, CacheStoreProc, wordsPerPage];

CacheModelImpl: CEDAR PROGRAM

IMPORTS Basics, DragOpsCrossUtils

EXPORTS CacheModel

= BEGIN OPEN DragOpsCross, DragOpsCrossUtils, CacheModel;

Word: TYPE = DragOpsCross.Word;

CacheBase: TYPE = REF CacheBaseRep;

CacheBaseRep: TYPE = RECORD [

sharedBase: SharedBase ← NIL, -- shared base data

private: REF ← NIL, -- private data to the cache implementation

fetch: CacheFetchProc ← NIL, -- this hook allows the user to intercept cache accesses

store: CacheStoreProc ← NIL, -- this hook allows the user to intercept cache accesses

data: REF ← NIL, -- private data for clients intercepting fetch & store

stats: CacheStats ← [] -- maintained by the default fetch and store routines

];

SharedBase: TYPE = REF SharedBaseRep;

SharedBaseRep: TYPE = RECORD [

mem: SparseMemory.Base ← NIL,

busyUntil: INT ← 0

];

CacheFetchProc: TYPE = PROC [base: CacheBase, addr: Word];

This is the type of routine that is used to fetch words from the cache.

CacheStoreProc: TYPE = PROC [base: CacheBase, addr: Word];

This is the type of routine that is used to store words into the cache.

CacheStats: TYPE = RECORD [

probes: INT ← 0,

chunkMisses: INT ← 0,

lineMisses: INT ← 0,

mapMisses: INT ← 0,

dirtyWrites: INT ← 0

];

Private types

wordsPerQuad: NAT = 4;

logWordsPerQuad: NAT = 2;

maxQuadsPerLine: NAT = 8;

wordsPerPage: CARDINAL = CacheModel.wordsPerPage;

QuadIndex: TYPE = [0..maxQuadsPerLine);

PageEntry: TYPE = REF PageEntryRep;

PageEntryRep: TYPE = RECORD [

next: PageEntry ← NIL,

pageAddr: Word ← ZerosWord,

useCount: INT ← 0

];

None: PACKED ARRAY QuadIndex OF BOOL = ALL[FALSE];

HashEntry: TYPE = REF HashEntryRep;

HashEntryRep: TYPE = RECORD [

next: HashEntry ← NIL,

lineAddr: Word ← ZerosWord,

index: NAT ←,

chunkPresent: PACKED ARRAY QuadIndex OF BOOL ← None,

dirty: PACKED ARRAY QuadIndex OF BOOL ← None,

referenced: PACKED ARRAY QuadIndex OF BOOL ← None

];

CacheData: TYPE = REF CacheDataRep;

CacheDataRep: TYPE = RECORD [

hashVector: HashVector ← NIL,

pageEntryCount: INT ← 0,

pageList: PageEntry ← NIL,

freePageList: PageEntry ← NIL,

victimIndex: CARDINAL ← 0,

lru: BOOL ← FALSE,

rover: NAT ← 0,

quadsPerLine: NAT ← 2,

lineTable: SEQUENCE linesInCache: NAT OF HashEntry

];

HashLim: CARDINAL = 512;

HashVector: TYPE = REF HashVectorRep;

HashVectorRep: TYPE = ARRAY [0..HashLim) OF HashEntry;

NewCache: PUBLIC PROC [lines: [0..4096), quadsPerLine: [0..8), lru: BOOL ← FALSE] RETURNS [CacheBase] = {

Creates a new cache on the specified shared memory.

base: CacheBase ← NEW[CacheBaseRep ← [NIL, LocalFetch, LocalStore, NIL, []]];

private: CacheData ←

NEW[CacheDataRep[lines] ← [quadsPerLine: quadsPerLine, lru: lru, lineTable: NULL]];

base.private ← private;

ResetCache[base];

RETURN [base];

};

ResetCache: PUBLIC PROC [cache: CacheBase] = {

Resets the given cache to its initial state (all empty).

private: CacheData = NARROW[cache.private];

private.pageList ← NIL;

private.hashVector ← NEW[HashVectorRep ← ALL[NIL]];

private.victimIndex ← 0;

private.pageEntryCount ← 0;

FOR i: NAT IN [0..private.linesInCache) DO

private[i] ← NEW[HashEntryRep ← [index: i]];

ENDLOOP;

cache.stats ← []; -- zero out statistics

};

FlushCache: PUBLIC PROC [cache: CacheBase] = {

Resets the given cache to its initial state (all empty).

private: CacheData = NARROW[cache.private];

private.pageList ← NIL;

private.hashVector^ ← ALL[NIL];

private.victimIndex ← 0;

private.pageEntryCount ← 0;

FOR i: NAT IN [0..private.linesInCache) DO

private[i]^ ← [index: i];

ENDLOOP;

};

LocalFetch: CacheFetchProc = {

[base: CacheBase, addr: Word];

private: CacheData = NARROW[base.private];

wordsPerLine: NAT = private.quadsPerLine * wordsPerQuad;

indexInLine: NAT = HalfToCard[LowHalf[addr]] MOD wordsPerLine;

chunk: QuadIndex = Basics.BITSHIFT[indexInLine, -logWordsPerQuad];

entry: HashEntry ← Access[base, AddDelta[addr, -INT[indexInLine]], chunk, fromJump];

entry ← entry; -- to have a place to set a breakpoint

};

LocalStore: CacheStoreProc = {

[base: CacheBase, addr: Word];

private: CacheData = NARROW[base.private];

wordsPerLine: NAT = private.quadsPerLine * wordsPerQuad;

indexInLine: NAT = HalfToCard[LowHalf[addr]] MOD wordsPerLine;

chunk: QuadIndex = Basics.BITSHIFT[indexInLine, -logWordsPerQuad];

hashEntry: HashEntry;

hashEntry ← Access[base, AddDelta[addr, -INT[indexInLine]], chunk, FALSE];

hashEntry.dirty[chunk] ← TRUE;

};

Method: TYPE = {advanceOnMiss, shiftOnHit};

method: Method ← shiftOnHit;

Access: PROC

[cache: CacheBase, lineAddr: Word, chunk: QuadIndex, fromJump: BOOL]

RETURNS [hashEntry: HashEntry] = {

data: CacheData = NARROW[cache.private];

oldEntry: BOOL ← TRUE;

victim: CARDINAL ← data.victimIndex;

hashIndex: CARDINAL;

halfHash: Half ← HalfXor[WordToHalves[lineAddr][0], WordToHalves[lineAddr][1]];

halfHash ← HalfXor[halfHash, HalfShift[halfHash, -8]];

hashIndex ← HalfToCard[halfHash] MOD HashLim;

hashEntry ← data.hashVector[hashIndex];

cache.stats.probes ← cache.stats.probes + 1;

WHILE hashEntry # NIL DO

IF hashEntry.lineAddr = lineAddr THEN {

IF data.lru THEN hashEntry.referenced[chunk] ← TRUE;

IF hashEntry.index = victim AND method = shiftOnHit THEN {

We make the victim index point at the next cache entry

victim ← victim + 1;

data.victimIndex ← IF victim = data.linesInCache THEN 0 ELSE victim;

};

IF ~hashEntry.chunkPresent[chunk] THEN {

IF fromJump THEN cache.stats.jumpMisses ← cache.stats.jumpMisses + 1;

cache.stats.chunkMisses ← cache.stats.chunkMisses + 1;

hashEntry.chunkPresent[chunk] ← TRUE};

RETURN;

};

hashEntry ← hashEntry.next;

ENDLOOP;

IF fromJump THEN cache.stats.jumpMisses ← cache.stats.jumpMisses + 1;

cache.stats.lineMisses ← cache.stats.lineMisses + 1;

hashEntry ← data.lineTable[victim];

{

The victim must be removed from the hash table and page table.

lag: PageEntry ← NIL;

oldLineAddr: Word = hashEntry.lineAddr;

oldIndexInPage: CARDINAL = HalfToCard[LowHalf[oldLineAddr]] MOD wordsPerPage;

oldPageAddr: Word = AddDelta[oldLineAddr, -INT[oldIndexInPage]];

headHashEntry: HashEntry;

oldHashIndex: CARDINAL;

oldHalfHash: Half ← HalfXor[

WordToHalves[oldLineAddr][0], WordToHalves[oldLineAddr][1]];

oldHalfHash ← HalfXor[oldHalfHash, HalfShift[oldHalfHash, -8]];

oldHashIndex ← HalfToCard[oldHalfHash] MOD HashLim;

headHashEntry ← data.hashVector[oldHashIndex];

Maintain the hash table by removing the victim from the table. We must be prepared for the entry to not be in the hash table at all if the entry is brand new.

IF headHashEntry = hashEntry

THEN data.hashVector[oldHashIndex] ← hashEntry.next

ELSE WHILE headHashEntry # NIL DO

IF hashEntry = headHashEntry.next THEN {

headHashEntry.next ← hashEntry.next;

EXIT};

headHashEntry ← headHashEntry.next

ENDLOOP;

Now we need to maintain the page table. We must be prepared for the entry to not be in the hash table at all if the entry is brand new.

FOR pageEntry: PageEntry ← data.pageList, pageEntry.next WHILE pageEntry # NIL DO

IF pageEntry.pageAddr = oldPageAddr THEN {

Decrement the use count for this page (if an entry already exists)

IF (pageEntry.useCount ← pageEntry.useCount - 1) <= 0 THEN {

Remove this page entry from the list and put it on the free page list.

IF lag = NIL THEN data.pageList ← pageEntry.next ELSE lag.next ← pageEntry.next;

data.pageEntryCount ← data.pageEntryCount - 1;

pageEntry.next ← data.freePageList;

data.freePageList ← pageEntry;

};

EXIT

};

lag ← pageEntry;

ENDLOOP;

IF hashEntry.dirty # None THEN {

FOR i: NAT IN [0..data.quadsPerLine) DO

IF hashEntry.dirty[i] THEN cache.stats.dirtyWrites ← cache.stats.dirtyWrites + 1;

ENDLOOP;

hashEntry.dirty ← None;

};

At this point we need to read in the quad word from the memory.

{

indexInPage: CARDINAL = HalfToCard[LowHalf[lineAddr]] MOD wordsPerPage;

pageAddr: Word = AddDelta[lineAddr, -INT[indexInPage]];

pageEntry: PageEntry ← data.pageList;

Maintain the hash table

hashEntry.next ← data.hashVector[hashIndex];

data.hashVector[hashIndex] ← hashEntry;

hashEntry.lineAddr ← lineAddr;

hashEntry.chunkPresent ← None; hashEntry.chunkPresent[chunk] ← TRUE;

WHILE pageEntry # NIL DO

IF pageEntry.pageAddr = pageAddr THEN {

Increment the use count for this page (if an entry already exists). Then return.

pageEntry.useCount ← pageEntry.useCount + 1;

GO TO oldEntry;

};

pageEntry ← pageEntry.next;

ENDLOOP;

This entry is brand new, so add it to the list and bump the reject cycles to show that we got a map miss. Note that at this point pageEntry = NIL.

data.pageEntryCount ← data.pageEntryCount + 1;

cache.stats.mapMisses ← cache.stats.mapMisses + 1;

pageEntry ← data.freePageList;

IF pageEntry = NIL

THEN pageEntry ← NEW[PageEntryRep]

ELSE data.freePageList ← pageEntry.next;

pageEntry^ ← [next: data.pageList, pageAddr: pageAddr, useCount: 1];

data.pageList ← pageEntry;

EXITS oldEntry => NULL;

};

At this point we have to advance the victim pointer, since in either method this newly retrieved entry clearly should not be the new victim.

victim ← victim + 1;

data.victimIndex ← IF victim = data.linesInCache THEN 0 ELSE victim;

};

END.