Private types
Cache: TYPE = CacheModels.Cache;
wordsPerQuad: NAT = 4;
logWordsPerQuad: NAT = 2;
maxQuadsPerLine: NAT = 8;
wordsPerPage: CARDINAL = CacheModels.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 [
stats: CacheStats ← [],
hashVector: HashVector ← NIL,
pageEntryCount: INT ← 0,
pageList: PageEntry ← NIL,
freePageList: PageEntry ← NIL,
victimIndex: CARDINAL ← 0,
lru: BOOL ← FALSE,
rover: NAT ← 0,
quadsPerLine: NAT ← 2,
realCache: CacheModels.Cache ← NIL,
lineTable: SEQUENCE linesInCache: NAT OF HashEntry
];
CacheStats:
TYPE =
RECORD [
probes: INT ← 0,
readProbes: INT ← 0,
writeProbes: INT ← 0,
writeMisses: INT ← 0,
writeClean: INT ← 0,
chunkMisses: INT ← 0,
lineMisses: INT ← 0,
jumpMisses: INT ← 0,
mapMisses: INT ← 0,
dirtyWrites: INT ← 0
];
HashLim: CARDINAL = 512;
HashVector: TYPE = REF HashVectorRep;
HashVectorRep: TYPE = ARRAY [0..HashLim) OF HashEntry;
NewCache:
PUBLIC
PROC [lines: [0..4096) ← 100, quadsPerLine: [0..8) ← 2, lru:
BOOL ←
FALSE, realCache: CacheModels.Cache]
RETURNS [cache: CacheModels.Cache] = {
Creates a new cache on the specified shared memory.
cache ←
NEW[CacheModels.CacheRec ← [
private: NEW[CacheDataRep[lines] ← [quadsPerLine: quadsPerLine, lru: lru, realCache: realCache, lineTable: NULL]],
fetch: Fetch, store: Store, reset: Reset, flush: Flush, print: Print,
data: NIL]];
Reset[cache];
};
Reset: CacheModels
.CacheResetProc
-- [cache: CacheModels.Cache] -- = {
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;
private.stats ← []; -- zero out statistics
private.realCache.reset[private.realCache];
};
Print: CacheModels.CachePrintProc
-- [cache: CacheModels.Cache, stream: STREAM, name: ROPE, resetStatistics: BOOL ← TRUE] -- = {
Realn:
PROC [r:
REAL, n:
NAT]
RETURNS [
IO.Value] = {
RETURN [[rope[Convert.RopeFromReal[r, n]]]]};
private: CacheData = NARROW[cache.private];
quadMisses: INT ← private.stats.chunkMisses;
misses: INT ← quadMisses + private.stats.lineMisses;
probes: INT ← private.stats.probes;
rProbes: REAL ← probes;
rMisses: REAL ← misses;
stream.PutF[
"\nStats for %g (lines: %g, quads/line: %g)\n probes: %g\n",
[rope[IF private.lru THEN Rope.Cat[name, " (pseudo-lru)"] ELSE name]],
[integer[private.linesInCache]], [integer[private.quadsPerLine]], [integer[probes]]];
IF probes = 0 THEN RETURN;
stream.PutF[
"read probes: %g, write probes: %g\n",
[integer[private.stats.readProbes]], [integer[private.stats.writeProbes]]];
stream.PutF[
"write misses: %g, writes to clean quads: %g\n",
[integer[private.stats.writeMisses]], [integer[private.stats.writeClean]]];
stream.PutF[
" misses: %g (%g (%g%%) existing line)\n",
[integer[misses]], [integer[private.stats.chunkMisses]],
IF misses = 0 THEN [rope["-"]] ELSE Realn[(quadMisses/rMisses)*100, 3]];
IF private.stats.jumpMisses # 0
THEN stream.PutF[
" misses caused by jumps: %g (%g%% of probes)\n",
[integer[private.stats.jumpMisses]], Realn[(private.stats.jumpMisses/rProbes)*100, 3]];
IF probes # 0
THEN stream.PutF[
" miss rate: %g%%\n",
Realn[(misses/rProbes)*100, 3]];
stream.PutF[
" map misses: %g\n dirty writes: %g\n",
[integer[private.stats.mapMisses]], [integer[private.stats.dirtyWrites]]];
};
Access:
PROC [cache: Cache, addr: Word, fromJump, write:
BOOL] = {
directMapped: BOOL = FALSE;
data: CacheData = NARROW[cache.private];
oldEntry: BOOL ← TRUE;
victim: CARDINAL ← data.victimIndex;
wordsPerLine: NAT = data.quadsPerLine * wordsPerQuad;
indexInLine: NAT = HalfToCard[LowHalf[addr]] MOD wordsPerLine;
chunk: QuadIndex = Basics.BITSHIFT[indexInLine, -logWordsPerQuad];
lineAddr: Word = AddDelta[addr, -INT[indexInLine]];
hashIndex: CARDINAL;
hashEntry: HashEntry;
halfHash: Half ← HalfXor[WordToHalves[lineAddr][0], WordToHalves[lineAddr][1]];
data.stats.probes ← data.stats.probes + 1;
IF write THEN data.stats.writeProbes ← data.stats.writeProbes + 1 ELSE data.stats.readProbes ← data.stats.readProbes + 1;
IF directMapped
THEN {
hashIndex ← (HalfToCard[LowHalf[lineAddr]] / wordsPerQuad) MOD data.linesInCache;
hashEntry ← data.lineTable[hashIndex];
IF hashEntry.lineAddr # lineAddr
THEN {
IF fromJump THEN data.stats.jumpMisses ← data.stats.jumpMisses + 1;
data.stats.lineMisses ← data.stats.lineMisses + 1;
IF write THEN data.stats.writeMisses ← data.stats.writeMisses + 1;
IF hashEntry.dirty # None
THEN {
FOR i:
NAT
IN [0..data.quadsPerLine)
DO
IF hashEntry.dirty[i]
THEN {
data.realCache.store[data.realCache, AddDelta[hashEntry.lineAddr, i]];
data.stats.dirtyWrites ← data.stats.dirtyWrites + 1;
};
ENDLOOP;
hashEntry.dirty ← None;
};
data.realCache.fetch[data.realCache, addr];
hashEntry.lineAddr ← lineAddr;
};
IF write
THEN {
IF NOT hashEntry.dirty[chunk] THEN data.stats.writeClean ← data.stats.writeClean + 1;
hashEntry.dirty[chunk] ← TRUE;
};
RETURN;
};
halfHash ← HalfXor[halfHash, HalfShift[halfHash, -8]];
hashIndex ← HalfToCard[halfHash] MOD HashLim;
hashEntry ← data.hashVector[hashIndex];
WHILE hashEntry #
NIL
DO
IF hashEntry.lineAddr = lineAddr
THEN {
IF data.lru THEN hashEntry.referenced[chunk] ← TRUE;
IF write
THEN {
IF NOT hashEntry.dirty[chunk] THEN data.stats.writeClean ← data.stats.writeClean + 1;
hashEntry.dirty[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 {
data.realCache.fetch[data.realCache, addr];
IF write THEN data.stats.writeMisses ← data.stats.writeMisses + 1;
IF fromJump THEN data.stats.jumpMisses ← data.stats.jumpMisses + 1;
data.stats.chunkMisses ← data.stats.chunkMisses + 1;
hashEntry.chunkPresent[chunk] ← TRUE};
RETURN;
};
hashEntry ← hashEntry.next;
ENDLOOP;
IF fromJump THEN data.stats.jumpMisses ← data.stats.jumpMisses + 1;
data.stats.lineMisses ← data.stats.lineMisses + 1;
IF write THEN data.stats.writeMisses ← data.stats.writeMisses + 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 {
data.realCache.store[data.realCache, AddDelta[oldLineAddr, i]];
data.stats.dirtyWrites ← data.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;
data.realCache.fetch[data.realCache, addr];
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;
data.stats.mapMisses ← data.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;
};
IF write
THEN {
IF NOT hashEntry.dirty[chunk] THEN data.stats.writeClean ← data.stats.writeClean + 1;
hashEntry.dirty[chunk] ← TRUE;
};
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;