/*
- * Copyright (c) 2012-2013 ARM Limited
+ * Copyright (c) 2012-2013, 2015 ARM Limited
* All rights reserved.
*
* The license below extends only to copyright in the software and shall
/** Write/writeback buffer */
MSHRQueue writeBuffer;
+ /**
+ * Allocate a buffer, passing the time indicating when schedule an
+ * event to the queued port to go and ask the MSHR and write queue
+ * if they have packets to send.
+ *
+ * allocateBufferInternal() function is called in:
+ * - MSHR allocateWriteBuffer (unchached write forwarded to WriteBuffer);
+ * - MSHR allocateMissBuffer (cacheable miss in MSHR queue);
+ * - MSHR allocateUncachedReadBuffer (unchached read allocated in MSHR
+ * queue)
+ */
MSHR *allocateBufferInternal(MSHRQueue *mq, Addr addr, int size,
PacketPtr pkt, Tick time, bool requestBus)
{
const unsigned blkSize;
/**
- * The latency of a hit in this device.
+ * The latency of tag lookup of a cache. It occurs when there is
+ * an access to the cache.
*/
- const Cycles hitLatency;
+ const Cycles lookupLatency;
+
+ /**
+ * This is the forward latency of the cache. It occurs when there
+ * is a cache miss and a request is forwarded downstream, in
+ * particular an outbound miss.
+ */
+ const Cycles forwardLatency;
+
+ /** The latency to fill a cache block */
+ const Cycles fillLatency;
/**
- * The latency of sending reponse to its upper level cache/core on a
- * linefill. In most contemporary processors, the return path on a cache
- * miss is much quicker that the hit latency. The responseLatency parameter
- * tries to capture this latency.
+ * The latency of sending reponse to its upper level cache/core on
+ * a linefill. The responseLatency parameter captures this
+ * latency.
*/
const Cycles responseLatency;
/*
- * Copyright (c) 2010-2014 ARM Limited
+ * Copyright (c) 2010-2015 ARM Limited
* All rights reserved.
*
* The license below extends only to copyright in the software and shall
if (pkt->req->isUncacheable()) {
uncacheableFlush(pkt);
blk = NULL;
- lat = hitLatency;
+ // lookupLatency is the latency in case the request is uncacheable.
+ lat = lookupLatency;
return false;
}
int id = pkt->req->hasContextId() ? pkt->req->contextId() : -1;
+ // Here lat is the value passed as parameter to accessBlock() function
+ // that can modify its value.
blk = tags->accessBlock(pkt->getAddr(), pkt->isSecure(), lat, id);
DPRINTF(Cache, "%s%s %x (%s) %s %s\n", pkt->cmdString(),
{
DPRINTF(Cache, "%s for %s address %x size %d\n", __func__,
pkt->cmdString(), pkt->getAddr(), pkt->getSize());
- Tick time = clockEdge(hitLatency);
assert(pkt->isResponse());
delete rec;
// @todo someone should pay for this
pkt->firstWordDelay = pkt->lastWordDelay = 0;
- memSidePort->schedTimingSnoopResp(pkt, time);
+ // forwardLatency is set here because there is a response from an
+ // upper level cache.
+ memSidePort->schedTimingSnoopResp(pkt, clockEdge(forwardLatency));
+
}
template<class TagStore>
delete pendingDelete[x];
pendingDelete.clear();
- // we charge hitLatency for doing just about anything here
- Tick time = clockEdge(hitLatency);
-
assert(pkt->isRequest());
// Just forward the packet if caches are disabled.
// prefetching (cache loading) uncacheable data is nonsensical
pkt->makeTimingResponse();
std::memset(pkt->getPtr<uint8_t>(), 0xFF, pkt->getSize());
- cpuSidePort->schedTimingResp(pkt, clockEdge(hitLatency));
+ // We use lookupLatency here because the request is uncacheable
+ cpuSidePort->schedTimingResp(pkt, clockEdge(lookupLatency));
return true;
} else if (pkt->isWrite() && !pkt->isRead()) {
- allocateWriteBuffer(pkt, time, true);
+ // We use forwardLatency here because there is an uncached
+ // memory write, forwarded to WriteBuffer. It specifies the
+ // latency to allocate an internal buffer and to schedule an
+ // event to the queued port.
+ allocateWriteBuffer(pkt, clockEdge(forwardLatency), true);
} else {
- allocateUncachedReadBuffer(pkt, time, true);
+ // We use forwardLatency here because there is an uncached
+ // memory read, allocateded to MSHR queue (it requires the same
+ // time of forwarding to WriteBuffer, in our assumption). It
+ // specifies the latency to allocate an internal buffer and to
+ // schedule an event to the queued port.
+ allocateUncachedReadBuffer(pkt, clockEdge(forwardLatency), true);
}
assert(pkt->needsResponse()); // else we should delete it here??
return true;
}
- Cycles lat = hitLatency;
+ // We use lookupLatency here because it is used to specify the latency
+ // to access.
+ Cycles lat = lookupLatency;
BlkType *blk = NULL;
PacketList writebacks;
-
+ // Note that lat is passed by reference here. The function access() calls
+ // accessBlock() which can modify lat value.
bool satisfied = access(pkt, blk, lat, writebacks);
// track time of availability of next prefetch, if any
pkt->makeTimingResponse();
// @todo: Make someone pay for this
pkt->firstWordDelay = pkt->lastWordDelay = 0;
+
+ // In this case we are considering lat neglecting
+ // responseLatency, modelling hit latency just as
+ // lookupLatency We pass lat by reference to access(),
+ // which calls accessBlock() function. If it is a hit,
+ // accessBlock() can modify lat to override the
+ // lookupLatency value.
cpuSidePort->schedTimingResp(pkt, clockEdge(lat));
} else {
/// @todo nominally we should just delete the packet here,
if (mshr->threadNum != 0/*pkt->req->threadId()*/) {
mshr->threadNum = -1;
}
- mshr->allocateTarget(pkt, time, order++);
+ // We use forwardLatency here because it is the same
+ // considering new targets. We have multiple requests for the
+ // same address here. It pecifies the latency to allocate an
+ // internal buffer and to schedule an event to the queued
+ // port.
+ mshr->allocateTarget(pkt, clockEdge(forwardLatency), order++);
if (mshr->getNumTargets() == numTarget) {
noTargetMSHR = mshr;
setBlocked(Blocked_NoTargets);
// no-write-allocate or bypass accesses this will have to
// be changed.
if (pkt->cmd == MemCmd::Writeback) {
- allocateWriteBuffer(pkt, time, true);
+ // We use forwardLatency here because there is an
+ // uncached memory write, forwarded to WriteBuffer. It
+ // specifies the latency to allocate an internal buffer and to
+ // schedule an event to the queued port.
+ allocateWriteBuffer(pkt, clockEdge(forwardLatency), true);
} else {
if (blk && blk->isValid()) {
// If we have a write miss to a valid block, we
assert(!blk->isWritable());
blk->status &= ~BlkReadable;
}
-
- allocateMissBuffer(pkt, time, true);
+ // Here we are using forwardLatency, modelling the latency of
+ // a miss (outbound) just as forwardLatency, neglecting the
+ // lookupLatency component. In this case this latency value
+ // specifies the latency to allocate an internal buffer and to
+ // schedule an event to the queued port, when a cacheable miss
+ // is forwarded to MSHR queue.
+ allocateMissBuffer(pkt, clockEdge(forwardLatency), true);
}
if (prefetcher) {
}
}
}
-
+ // Here we condiser just forward latency.
if (next_pf_time != MaxTick)
- requestMemSideBus(Request_PF, std::max(time, next_pf_time));
-
+ requestMemSideBus(Request_PF, std::max(clockEdge(forwardLatency),
+ next_pf_time));
// copy writebacks to write buffer
while (!writebacks.empty()) {
PacketPtr wbPkt = writebacks.front();
- allocateWriteBuffer(wbPkt, time, true);
+ // We use forwardLatency here because we are copying writebacks
+ // to write buffer. It specifies the latency to allocate an internal
+ // buffer and to schedule an event to the queued port.
+ allocateWriteBuffer(wbPkt, clockEdge(forwardLatency), true);
writebacks.pop_front();
}
Tick
Cache<TagStore>::recvAtomic(PacketPtr pkt)
{
- Cycles lat = hitLatency;
-
+ // We are in atomic mode so we pay just for lookupLatency here.
+ Cycles lat = lookupLatency;
// @TODO: make this a parameter
bool last_level_cache = false;
{
assert(pkt->isResponse());
- Tick time = clockEdge(hitLatency);
MSHR *mshr = dynamic_cast<MSHR*>(pkt->senderState);
bool is_error = pkt->isError();
// copy writebacks to write buffer
while (!writebacks.empty()) {
PacketPtr wbPkt = writebacks.front();
- allocateWriteBuffer(wbPkt, time, true);
+ allocateWriteBuffer(wbPkt, clockEdge(forwardLatency), true);
writebacks.pop_front();
}
// if we used temp block, clear it out
if (blk == tempBlock) {
if (blk->isDirty()) {
- allocateWriteBuffer(writebackBlk(blk), time, true);
+ // We use forwardLatency here because we are copying
+ // writebacks to write buffer. It specifies the latency to
+ // allocate an internal buffer and to schedule an event to the
+ // queued port.
+ allocateWriteBuffer(writebackBlk(blk), clockEdge(forwardLatency),
+ true);
}
blk->invalidate();
}
assert(pkt->hasData());
std::memcpy(blk->data, pkt->getConstPtr<uint8_t>(), blkSize);
}
-
- blk->whenReady = clockEdge() + responseLatency * clockPeriod() +
+ // We pay for fillLatency here.
+ blk->whenReady = clockEdge() + fillLatency * clockPeriod() +
pkt->lastWordDelay;
return blk;
}
DPRINTF(Cache, "%s created response: %s address %x size %d\n",
__func__, pkt->cmdString(), pkt->getAddr(), pkt->getSize());
- memSidePort->schedTimingSnoopResp(pkt, clockEdge(hitLatency));
+ // We model a snoop just considering forwardLatency
+ memSidePort->schedTimingSnoopResp(pkt, clockEdge(forwardLatency));
}
template<class TagStore>
BlkType *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
handleSnoop(pkt, blk, false, false, false);
- return hitLatency * clockPeriod();
+ // We consider forwardLatency here because a snoop occurs in atomic mode
+ return forwardLatency * clockPeriod();
}
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