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mem: Remove WriteInvalidate support

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Prepare for a different implementation following in the next patch
This commit is contained in:
Curtis Dunham 2014-12-02 06:08:17 -05:00
parent df37cad0fd
commit 7ca27dd3cc
5 changed files with 25 additions and 211 deletions
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1
src/mem/cache/base.hh vendored
View file

@ -94,7 +94,6 @@ class BaseCache : public MemObject
Blocked_NoMSHRs = MSHRQueue_MSHRs,
Blocked_NoWBBuffers = MSHRQueue_WriteBuffer,
Blocked_NoTargets,
Blocked_PendingWriteInvalidate,
NUM_BLOCKED_CAUSES
};

3
src/mem/cache/blk.hh vendored
View file

@ -73,9 +73,6 @@ enum CacheBlkStatusBits {
BlkHWPrefetched = 0x20,
/** block holds data from the secure memory space */
BlkSecure = 0x40,
/** can the block transition to E? (hasn't been shared with another cache)
* used to close a timing gap when handling WriteInvalidate packets */
BlkCanGoExclusive = 0x80
};
/**

189
src/mem/cache/cache_impl.hh vendored
View file

@ -70,7 +70,7 @@ Cache<TagStore>::Cache(const Params *p)
: BaseCache(p),
tags(dynamic_cast<TagStore*>(p->tags)),
prefetcher(p->prefetcher),
doFastWrites(true),
doFastWrites(false),
prefetchOnAccess(p->prefetch_on_access)
{
tempBlock = new BlkType();
@ -321,20 +321,15 @@ Cache<TagStore>::access(PacketPtr pkt, BlkType *&blk,
pkt->getAddr(), pkt->isSecure() ? "s" : "ns",
blk ? "hit" : "miss", blk ? blk->print() : "");
// Writeback handling is special case. We can write the block
// into the cache without having a writeable copy (or any copy at
// all). Like writebacks, we write into the cache upon initial
// receipt of a write-invalidate packets as well.
if ((pkt->cmd == MemCmd::Writeback) ||
((pkt->cmd == MemCmd::WriteInvalidateReq) && isTopLevel)) {
// Writeback handling is special case. We can write the block into
// the cache without having a writeable copy (or any copy at all).
if (pkt->cmd == MemCmd::Writeback) {
assert(blkSize == pkt->getSize());
if (blk == NULL) {
// need to do a replacement
blk = allocateBlock(pkt->getAddr(), pkt->isSecure(), writebacks);
if (blk == NULL) {
// no replaceable block available, give up.
// Writeback will be forwarded to next level,
// WriteInvalidate will be retried.
// no replaceable block available: give up, fwd to next level.
incMissCount(pkt);
return false;
}
@ -345,29 +340,16 @@ Cache<TagStore>::access(PacketPtr pkt, BlkType *&blk,
blk->status |= BlkSecure;
}
}
if (pkt->cmd == MemCmd::Writeback) {
blk->status |= BlkDirty;
if (pkt->isSupplyExclusive()) {
blk->status |= BlkWritable;
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
} else if (pkt->cmd == MemCmd::WriteInvalidateReq) {
blk->status |= (BlkReadable | BlkDirty | BlkCanGoExclusive);
blk->status &= ~BlkWritable;
++fastWrites;
blk->status |= BlkDirty;
if (pkt->isSupplyExclusive()) {
blk->status |= BlkWritable;
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
std::memcpy(blk->data, pkt->getConstPtr<uint8_t>(), blkSize);
DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
incHitCount(pkt);
return true;
} else if ((pkt->cmd == MemCmd::WriteInvalidateReq) && !isTopLevel) {
if (blk != NULL) {
assert(blk != tempBlock);
tags->invalidate(blk);
blk->invalidate();
}
return true;
} else if ((blk != NULL) &&
(pkt->needsExclusive() ? blk->isWritable()
: blk->isReadable())) {
@ -550,18 +532,6 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt)
bool needsResponse = pkt->needsResponse();
if (pkt->cmd == MemCmd::WriteInvalidateReq) {
if (!satisfied && isTopLevel) {
// access() tried to allocate a block but it could not; abort.
setBlocked(Blocked_PendingWriteInvalidate);
return false;
}
satisfied = false;
// we need to take the miss path (allocate MSHR, etc.) for
// WriteInvalidates because they always need to propagate
// throughout the memory system
}
if (satisfied) {
// hit (for all other request types)
@ -591,16 +561,6 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt)
// @todo: Make someone pay for this
pkt->firstWordDelay = pkt->lastWordDelay = 0;
if (blk && blk->isValid() && (blk->status & BlkCanGoExclusive) &&
pkt->isWrite() && (pkt->cmd != MemCmd::WriteInvalidateReq)) {
// Packet is a Write (needs exclusive) should be delayed because
// a WriteInvalidate is pending. Instead of going the MSHR route,
// the Packet should be replayed, since if the block transitions
// to Exclusive the write can complete immediately.
setBlocked(Blocked_PendingWriteInvalidate);
return false;
}
Addr blk_addr = blockAlign(pkt->getAddr());
MSHR *mshr = mshrQueue.findMatch(blk_addr, pkt->isSecure());
@ -647,20 +607,7 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt)
pkt = pf;
}
if (pkt && (pkt->cmd == MemCmd::WriteInvalidateReq)) {
// WriteInvalidates cannot coalesce with other requests, so
// we cannot use an existing MSHR. If one exists, we mark it
// as 'obsolete' so they don't modify the cache.
if (mshr) {
// Everything up to this point is obsolete, meaning
// they should not modify the cache.
DPRINTF(Cache, "%s: marking MSHR obsolete in %s of %x\n",
__func__, pkt->cmdString(), pkt->getAddr());
mshr->markObsolete();
}
allocateMissBuffer(pkt, time, true);
} else if (mshr) {
if (mshr) {
/// MSHR hit
/// @note writebacks will be checked in getNextMSHR()
/// for any conflicting requests to the same block
@ -707,10 +654,7 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt)
if (pkt->cmd == MemCmd::Writeback) {
allocateWriteBuffer(pkt, time, true);
} else {
if (pkt->cmd == MemCmd::WriteInvalidateReq) {
// a WriteInvalidate is not a normal write miss;
// the assertions below are not applicable.
} else if (blk && blk->isValid()) {
if (blk && blk->isValid()) {
// If we have a write miss to a valid block, we
// need to mark the block non-readable. Otherwise
// if we allow reads while there's an outstanding
@ -769,12 +713,6 @@ Cache<TagStore>::getBusPacket(PacketPtr cpu_pkt, BlkType *blk,
return NULL;
}
// WriteInvalidates for cache line clearing instructions don't
// require a read; just send directly to the bus.
if (cpu_pkt->cmd == MemCmd::WriteInvalidateReq) {
return NULL;
}
if (!blkValid &&
(cpu_pkt->cmd == MemCmd::Writeback || cpu_pkt->isUpgrade())) {
// Writebacks that weren't allocated in access() and upgrades
@ -870,9 +808,6 @@ Cache<TagStore>::recvAtomic(PacketPtr pkt)
if (!access(pkt, blk, lat, writebacks)) {
// MISS
// WriteInvalidates should never fail an access() in Atomic mode
assert(pkt->cmd != MemCmd::WriteInvalidateReq);
PacketPtr bus_pkt = getBusPacket(pkt, blk, pkt->needsExclusive());
bool is_forward = (bus_pkt == NULL);
@ -943,29 +878,6 @@ Cache<TagStore>::recvAtomic(PacketPtr pkt)
delete wbPkt;
}
// We now have the block one way or another (hit or completed miss),
// except for Request types that perform an invalidate, where the point
// is to make sure there is no block.
if (pkt->cmd == MemCmd::WriteInvalidateReq) {
memSidePort->sendAtomic(pkt); // complete writeback
if (isTopLevel) {
// @todo Static analysis suggests this can actually happen
assert(blk);
// top level caches allocate and write the data
assert(blk->isDirty());
assert(!blk->isWritable());
assert(blk->status & BlkCanGoExclusive);
blk->status &= ~(BlkDirty | BlkCanGoExclusive); // and mark clean
blk->status |= BlkWritable; // i.e. O(+cgE) -> E
} else {
// other caches invalidate.
// if the block was found, it was invalidated.
assert(!blk || !blk->isValid());
}
}
if (pkt->needsResponse()) {
pkt->makeAtomicResponse();
}
@ -1101,10 +1013,7 @@ Cache<TagStore>::recvTimingResp(PacketPtr pkt)
bool is_fill = !mshr->isForward &&
(pkt->isRead() || pkt->cmd == MemCmd::UpgradeResp);
if (mshr->isObsolete()) {
DPRINTF(Cache, "%s: skipping cache fills; data for %s of %x "
"is obsolete\n", __func__, pkt->cmdString(), pkt->getAddr());
} else if (is_fill && !is_error) {
if (is_fill && !is_error) {
DPRINTF(Cache, "Block for addr %x being updated in Cache\n",
pkt->getAddr());
@ -1140,19 +1049,9 @@ Cache<TagStore>::recvTimingResp(PacketPtr pkt)
}
if (is_fill) {
// Presently the only situation leading to 'obsolete'
// data is when a WriteInvalidate blows away an already
// pending/in-progress read. We don't want to overwrite
// cache data in that case.
if (mshr->isObsolete()) {
DPRINTF(Cache, "%s: skipping satisfyCpuSideRequest; "
"data for %s of %x is obsolete\n",
__func__, target->pkt->cmdString(),
target->pkt->getAddr());
} else {
satisfyCpuSideRequest(target->pkt, blk,
true, mshr->hasPostDowngrade());
}
satisfyCpuSideRequest(target->pkt, blk,
true, mshr->hasPostDowngrade());
// How many bytes past the first request is this one
int transfer_offset =
target->pkt->getOffset(blkSize) - initial_offset;
@ -1184,38 +1083,6 @@ Cache<TagStore>::recvTimingResp(PacketPtr pkt)
completion_time = clockEdge(responseLatency) +
pkt->lastWordDelay;
target->pkt->req->setExtraData(0);
} else if (pkt->cmd == MemCmd::WriteInvalidateResp) {
if (blk) {
assert(blk->isDirty() && !blk->isWritable());
// The block, having been written back, is no longer dirty,
// nor do we have any reason to see if it was snooped in the
// meantime (which CanGoExclusive tracks). If it can go
// exclusive, we put it in that state, and otherwise S.
// In short: O(+cgE) -> E, O(-cgE) -> S
if (blk->status & BlkCanGoExclusive) {
blk->status |= BlkWritable;
}
blk->status &= ~(BlkDirty | BlkCanGoExclusive);
}
if (isTopLevel) {
// makeTimingResponse() will turn it into a WriteResp
target->pkt->cmd = MemCmd::WriteReq;
// Writes may have been blocked - quite rare case, but
// it does happen. Prevent deadlock by telling the core
if (isBlocked()) { // to retry.
clearBlocked(Blocked_PendingWriteInvalidate);
}
}
// If the block managed to get evicted before its own
// writeback (e.g. by a Read/Upgrade (from O(-cgE)/S to
// I/E) or ReadExclusive (direct to I/E); either way a
// cache-to-cache ownership transfer) completed, that's
// OK, we just ignore this response. If the new owner
// doesn't actually modify it, a superfluous writeback
// will occur for its impatience (since it will think it
// has dirty data), but it really can't be helped.
completion_time = clockEdge(responseLatency) +
pkt->lastWordDelay;
} else {
// not a cache fill, just forwarding response
// responseLatency is the latency of the return path
@ -1443,8 +1310,7 @@ Cache<TagStore>::allocateBlock(Addr addr, bool is_secure,
Addr repl_addr = tags->regenerateBlkAddr(blk->tag, blk->set);
MSHR *repl_mshr = mshrQueue.findMatch(repl_addr, blk->isSecure());
if (repl_mshr) {
// must be an outstanding upgrade request (common case)
// or WriteInvalidate pending writeback (very uncommon case)
// must be an outstanding upgrade request
// on a block we're about to replace...
assert(!blk->isWritable() || blk->isDirty());
assert(repl_mshr->needsExclusive());
@ -1532,20 +1398,10 @@ Cache<TagStore>::handleFill(PacketPtr pkt, BlkType *blk,
// there are cases (such as failed store conditionals or
// compare-and-swaps) where we'll demand an exclusive copy but
// end up not writing it.
// Caveat: if a Read takes a value from a WriteInvalidate MSHR,
// it will get marked Dirty even though it is Clean (once the
// WriteInvalidate completes). This is due to insufficient meta-
// data and overly presumptive interpretation of the inhibit flag.
// The result is an unnecessary extra writeback.
if (pkt->memInhibitAsserted())
blk->status |= BlkDirty;
}
if (pkt->cmd == MemCmd::WriteInvalidateReq) {
// a block written immediately, all at once, pre-writeback is dirty
blk->status |= BlkDirty;
}
DPRINTF(Cache, "Block addr %x (%s) moving from state %x to %s\n",
addr, is_secure ? "s" : "ns", old_state, blk->print());
@ -1683,13 +1539,8 @@ Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
// we may end up modifying both the block state and the packet (if
// we respond in atomic mode), so just figure out what to do now
// and then do it later. If we find dirty data while snooping for a
// WriteInvalidate, we don't care, since no merging needs to take place.
// We need the eviction to happen as normal, but the data needn't be
// sent anywhere, nor should the writeback be inhibited at the memory
// controller for any reason.
bool respond = blk->isDirty() && pkt->needsResponse()
&& (pkt->cmd != MemCmd::WriteInvalidateReq);
// and then do it later.
bool respond = blk->isDirty() && pkt->needsResponse();
bool have_exclusive = blk->isWritable();
// Invalidate any prefetch's from below that would strip write permissions
@ -1706,7 +1557,7 @@ Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
if (pkt->isRead() && !invalidate) {
assert(!needs_exclusive);
pkt->assertShared();
int bits_to_clear = BlkWritable | BlkCanGoExclusive;
int bits_to_clear = BlkWritable;
const bool haveOwnershipState = true; // for now
if (!haveOwnershipState) {
// if we don't support pure ownership (dirty && !writable),

25
src/mem/cache/mshr.cc vendored
View file

@ -62,9 +62,9 @@
using namespace std;
MSHR::MSHR() : readyTime(0), _isUncacheable(false), downstreamPending(false),
pendingDirty(false), pendingClean(false),
pendingDirty(false),
postInvalidate(false), postDowngrade(false),
_isObsolete(false), queue(NULL), order(0), addr(0),
queue(NULL), order(0), addr(0),
size(0), isSecure(false), inService(false),
isForward(false), threadNum(InvalidThreadID), data(NULL)
{
@ -214,9 +214,7 @@ MSHR::allocate(Addr _addr, int _size, PacketPtr target, Tick whenReady,
isForward = false;
_isUncacheable = target->req->isUncacheable();
inService = false;
pendingClean = (target->cmd == MemCmd::WriteInvalidateReq);
downstreamPending = false;
_isObsolete = false;
threadNum = 0;
assert(targets.isReset());
// Don't know of a case where we would allocate a new MSHR for a
@ -253,9 +251,8 @@ MSHR::markInService(PacketPtr pkt)
assert(pkt != NULL);
inService = true;
pendingDirty = ((targets.needsExclusive &&
(pkt->cmd != MemCmd::WriteInvalidateReq)) ||
(!pkt->sharedAsserted() && pkt->memInhibitAsserted()));
pendingDirty = targets.needsExclusive ||
(!pkt->sharedAsserted() && pkt->memInhibitAsserted());
postInvalidate = postDowngrade = false;
if (!downstreamPending) {
@ -374,12 +371,7 @@ MSHR::handleSnoop(PacketPtr pkt, Counter _order)
targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
downstreamPending && targets.needsExclusive);
// WriteInvalidates must writeback and should not be inhibited on
// account of its snoops discovering MSHRs wanting exclusive access
// to what it wrote. We don't want to push this check higher,
// however, because we want to be sure to add an invalidating
// Target::FromSnoop, above.
if (isPendingDirty() && (pkt->cmd != MemCmd::WriteInvalidateReq)) {
if (isPendingDirty()) {
pkt->assertMemInhibit();
pkt->setSupplyExclusive();
}
@ -387,13 +379,6 @@ MSHR::handleSnoop(PacketPtr pkt, Counter _order)
if (pkt->needsExclusive()) {
// This transaction will take away our pending copy
postInvalidate = true;
// Do not defer (i.e. return true) the snoop if the block is
// going to be clean once the MSHR completes, as the data is
// ready now.
if (isPendingClean()) {
return false;
}
}
}

18
src/mem/cache/mshr.hh vendored
View file

@ -83,18 +83,12 @@ class MSHR : public Packet::SenderState, public Printable
/** Will we have a dirty copy after this request? */
bool pendingDirty;
/** Will we have a clean copy after this request? (i.e. is writeback) */
bool pendingClean;
/** Did we snoop an invalidate while waiting for data? */
bool postInvalidate;
/** Did we snoop a read while waiting for data? */
bool postDowngrade;
/** Did we get WriteInvalidate'd (and therefore obsoleted)? */
bool _isObsolete;
public:
class Target {
@ -182,10 +176,6 @@ class MSHR : public Packet::SenderState, public Printable
assert(inService); return pendingDirty;
}
bool isPendingClean() const {
return pendingClean;
}
bool hasPostInvalidate() const {
assert(inService); return postInvalidate;
}
@ -224,8 +214,6 @@ class MSHR : public Packet::SenderState, public Printable
bool isUncacheable() const { return _isUncacheable; }
bool isObsolete() const { return _isObsolete; }
/**
* Allocate a miss to this MSHR.
* @param cmd The requesting command.
@ -301,12 +289,6 @@ class MSHR : public Packet::SenderState, public Printable
bool checkFunctional(PacketPtr pkt);
/** Mark this MSHR as tracking a transaction with obsoleted data. It still
* needs to complete its lifecycle, but should not modify the cache. */
void markObsolete() {
_isObsolete = true;
}
/**
* Prints the contents of this MSHR for debugging.
*/