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mem: Make tXAW enforcement less conservative and per rank

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This patch changes the tXAW constraint so that it is enforced per rank
rather than globally for all ranks in the channel. It also avoids
using the bank freeAt to enforce the activation limit, as doing so
also precludes performing any column or row command to the
DRAM. Instead the patch introduces a new variable actAllowedAt for the
banks and use this to track when a potential activation can occur.
This commit is contained in:
Ani Udipi 2013-11-01 11:56:22 -04:00
parent 7645c8e611
commit 8bc855fa15
2 changed files with 33 additions and 19 deletions
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44
src/mem/simple_dram.cc
View file

@ -55,7 +55,7 @@ SimpleDRAM::SimpleDRAM(const SimpleDRAMParams* p) :
AbstractMemory(p),
port(name() + ".port", *this),
retryRdReq(false), retryWrReq(false),
rowHitFlag(false), stopReads(false), actTicks(p->activation_limit, 0),
rowHitFlag(false), stopReads(false),
writeEvent(this), respondEvent(this),
refreshEvent(this), nextReqEvent(this), drainManager(NULL),
deviceBusWidth(p->device_bus_width), burstLength(p->burst_length),
@ -82,8 +82,10 @@ SimpleDRAM::SimpleDRAM(const SimpleDRAMParams* p) :
// create the bank states based on the dimensions of the ranks and
// banks
banks.resize(ranksPerChannel);
actTicks.resize(ranksPerChannel);
for (size_t c = 0; c < ranksPerChannel; ++c) {
banks[c].resize(banksPerRank);
actTicks[c].resize(activationLimit, 0);
}
// round the write threshold percent to a whole number of entries
@ -913,6 +915,7 @@ SimpleDRAM::estimateLatency(DRAMPacket* dram_pkt, Tick inTime)
Tick accLat = 0;
Tick bankLat = 0;
rowHitFlag = false;
Tick potentialActTick;
const Bank& bank = dram_pkt->bankRef;
if (pageMgmt == Enums::open) { // open-page policy
@ -946,6 +949,11 @@ SimpleDRAM::estimateLatency(DRAMPacket* dram_pkt, Tick inTime)
if (freeTime > inTime)
accLat += freeTime - inTime;
//The bank is free, and you may be able to activate
potentialActTick = inTime + accLat + tRP;
if (potentialActTick < bank.actAllowedAt)
accLat += bank.actAllowedAt - potentialActTick;
accLat += tRP + tRCD + tCL;
bankLat += tRP + tRCD + tCL;
}
@ -955,6 +963,11 @@ SimpleDRAM::estimateLatency(DRAMPacket* dram_pkt, Tick inTime)
if (bank.freeAt > inTime)
accLat += bank.freeAt - inTime;
//The bank is free, and you may be able to activate
potentialActTick = inTime + accLat;
if (potentialActTick < bank.actAllowedAt)
accLat += bank.actAllowedAt - potentialActTick;
// page already closed, simply open the row, and
// add cas latency
accLat += tRCD + tCL;
@ -975,42 +988,41 @@ SimpleDRAM::processNextReqEvent()
}
void
SimpleDRAM::recordActivate(Tick act_tick)
SimpleDRAM::recordActivate(Tick act_tick, uint8_t rank)
{
assert(actTicks.size() == activationLimit);
assert(0 <= rank && rank < ranksPerChannel);
assert(actTicks[rank].size() == activationLimit);
DPRINTF(DRAM, "Activate at tick %d\n", act_tick);
// if the activation limit is disabled then we are done
if (actTicks.empty())
if (actTicks[rank].empty())
return;
// sanity check
if (actTicks.back() && (act_tick - actTicks.back()) < tXAW) {
if (actTicks[rank].back() && (act_tick - actTicks[rank].back()) < tXAW) {
// @todo For now, stick with a warning
warn("Got %d activates in window %d (%d - %d) which is smaller "
"than %d\n", activationLimit, act_tick - actTicks.back(),
act_tick, actTicks.back(), tXAW);
"than %d\n", activationLimit, act_tick - actTicks[rank].back(),
act_tick, actTicks[rank].back(), tXAW);
}
// shift the times used for the book keeping, the last element
// (highest index) is the oldest one and hence the lowest value
actTicks.pop_back();
actTicks[rank].pop_back();
// record an new activation (in the future)
actTicks.push_front(act_tick);
actTicks[rank].push_front(act_tick);
// cannot activate more than X times in time window tXAW, push the
// next one (the X + 1'st activate) to be tXAW away from the
// oldest in our window of X
if (actTicks.back() && (act_tick - actTicks.back()) < tXAW) {
if (actTicks[rank].back() && (act_tick - actTicks[rank].back()) < tXAW) {
DPRINTF(DRAM, "Enforcing tXAW with X = %d, next activate no earlier "
"than %d\n", activationLimit, actTicks.back() + tXAW);
for(int i = 0; i < ranksPerChannel; i++)
"than %d\n", activationLimit, actTicks[rank].back() + tXAW);
for(int j = 0; j < banksPerRank; j++)
// next activate must not happen before end of window
banks[i][j].freeAt = std::max(banks[i][j].freeAt,
actTicks.back() + tXAW);
banks[rank][j].actAllowedAt = actTicks[rank].back() + tXAW;
}
}
@ -1049,7 +1061,7 @@ SimpleDRAM::doDRAMAccess(DRAMPacket* dram_pkt)
// any waiting for banks account for in freeAt
actTick = bank.freeAt - tCL - tRCD;
bank.tRASDoneAt = actTick + tRAS;
recordActivate(actTick);
recordActivate(actTick, dram_pkt->rank);
// sample the number of bytes accessed and reset it as
// we are now closing this row
@ -1058,7 +1070,7 @@ SimpleDRAM::doDRAMAccess(DRAMPacket* dram_pkt)
}
} else if (pageMgmt == Enums::close) {
actTick = curTick() + addDelay + accessLat - tRCD - tCL;
recordActivate(actTick);
recordActivate(actTick, dram_pkt->rank);
// If the DRAM has a very quick tRAS, bank can be made free
// after consecutive tCL,tRCD,tRP times. In general, however,

8
src/mem/simple_dram.hh
View file

@ -134,7 +134,7 @@ class SimpleDRAM : public AbstractMemory
bool stopReads;
/** List to keep track of activate ticks */
std::deque<Tick> actTicks;
std::vector<std::deque<Tick>> actTicks;
/**
* A basic class to track the bank state indirectly via times
@ -153,11 +153,13 @@ class SimpleDRAM : public AbstractMemory
Tick freeAt;
Tick tRASDoneAt;
Tick actAllowedAt;
uint32_t bytesAccessed;
Bank() :
openRow(INVALID_ROW), freeAt(0), tRASDoneAt(0), bytesAccessed(0)
openRow(INVALID_ROW), freeAt(0), tRASDoneAt(0), actAllowedAt(0),
bytesAccessed(0)
{ }
};
@ -418,7 +420,7 @@ class SimpleDRAM : public AbstractMemory
* method updates the time that the banks become available based
* on the current limits.
*/
void recordActivate(Tick act_tick);
void recordActivate(Tick act_tick, uint8_t rank);
void printParams() const;
void printQs() const;