From 8bc855fa15bc936cae8418a4b13eebc35526dff1 Mon Sep 17 00:00:00 2001 From: Ani Udipi Date: Fri, 1 Nov 2013 11:56:22 -0400 Subject: [PATCH] mem: Make tXAW enforcement less conservative and per rank 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. --- src/mem/simple_dram.cc | 44 +++++++++++++++++++++++++++--------------- src/mem/simple_dram.hh | 8 +++++--- 2 files changed, 33 insertions(+), 19 deletions(-) diff --git a/src/mem/simple_dram.cc b/src/mem/simple_dram.cc index 9669c7a03..bd700c09d 100644 --- a/src/mem/simple_dram.cc +++ b/src/mem/simple_dram.cc @@ -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, diff --git a/src/mem/simple_dram.hh b/src/mem/simple_dram.hh index 19d23efba..c97f70e1d 100644 --- a/src/mem/simple_dram.hh +++ b/src/mem/simple_dram.hh @@ -134,7 +134,7 @@ class SimpleDRAM : public AbstractMemory bool stopReads; /** List to keep track of activate ticks */ - std::deque actTicks; + std::vector> 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; -- 2.30.2