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authorAndreas Hansson <andreas.hansson@arm.com>2013-11-01 11:56:20 -0400
committerAndreas Hansson <andreas.hansson@arm.com>2013-11-01 11:56:20 -0400
commit10e8978ec0ee7a7443247d7a85ab0b3587740f1a (patch)
tree8d9021db468477d72983d77377883aa38cd97ca2
parentea76f9757668018ad1f2ccb50fd61b9288057913 (diff)
downloadgem5-10e8978ec0ee7a7443247d7a85ab0b3587740f1a.tar.xz
mem: Pick the next DRAM request based on bank availability
This patch changes the FCFS bit of FR-FCFS such that requests that target the earliest available bank are picked first (as suggested in the original work on FR-FCFS by Rixner et al). To accommodate this we add functionality to identify a bank through a one-dimensional identifier (bank id). The member names of the DRAMPacket are also update to match the style guide.
-rw-r--r--src/mem/simple_dram.cc97
-rw-r--r--src/mem/simple_dram.hh31
2 files changed, 102 insertions, 26 deletions
diff --git a/src/mem/simple_dram.cc b/src/mem/simple_dram.cc
index 62f825395..9cbca6a1c 100644
--- a/src/mem/simple_dram.cc
+++ b/src/mem/simple_dram.cc
@@ -39,9 +39,11 @@
*
* Authors: Andreas Hansson
* Ani Udipi
+ * Neha Agarwal
*/
#include "base/trace.hh"
+#include "base/bitfield.hh"
#include "debug/Drain.hh"
#include "debug/DRAM.hh"
#include "mem/simple_dram.hh"
@@ -191,7 +193,7 @@ SimpleDRAM::decodeAddr(PacketPtr pkt, Addr dramPktAddr, unsigned size, bool isRe
// Ra, Co, Ba and Ch denoting rank, column, bank and channel,
// respectively
uint8_t rank;
- uint16_t bank;
+ uint8_t bank;
uint16_t row;
// truncate the address to the access granularity
@@ -278,8 +280,9 @@ SimpleDRAM::decodeAddr(PacketPtr pkt, Addr dramPktAddr, unsigned size, bool isRe
// create the corresponding DRAM packet with the entry time and
// ready time set to the current tick, the latter will be updated
// later
- return new DRAMPacket(pkt, isRead, rank, bank, row, dramPktAddr, size,
- banks[rank][bank]);
+ uint16_t bank_id = banksPerRank * rank + bank;
+ return new DRAMPacket(pkt, isRead, rank, bank, row, bank_id, dramPktAddr,
+ size, banks[rank][bank]);
}
void
@@ -347,9 +350,8 @@ SimpleDRAM::addToReadQueue(PacketPtr pkt, unsigned int pktCount)
readQueue.push_back(dram_pkt);
// Update stats
- uint32_t bank_id = banksPerRank * dram_pkt->rank + dram_pkt->bank;
- assert(bank_id < ranksPerChannel * banksPerRank);
- perBankRdReqs[bank_id]++;
+ assert(dram_pkt->bankId < ranksPerChannel * banksPerRank);
+ perBankRdReqs[dram_pkt->bankId]++;
avgRdQLen = readQueue.size() + respQueue.size();
}
@@ -540,9 +542,8 @@ SimpleDRAM::addToWriteQueue(PacketPtr pkt, unsigned int pktCount)
writeQueue.push_back(dram_pkt);
// Update stats
- uint32_t bank_id = banksPerRank * dram_pkt->rank + dram_pkt->bank;
- assert(bank_id < ranksPerChannel * banksPerRank);
- perBankWrReqs[bank_id]++;
+ assert(dram_pkt->bankId < ranksPerChannel * banksPerRank);
+ perBankWrReqs[dram_pkt->bankId]++;
avgWrQLen = writeQueue.size();
}
@@ -781,18 +782,31 @@ SimpleDRAM::chooseNextWrite()
if (memSchedPolicy == Enums::fcfs) {
// Do nothing, since the correct request is already head
} else if (memSchedPolicy == Enums::frfcfs) {
+ // Only determine bank availability when needed
+ uint64_t earliest_banks = 0;
+
auto i = writeQueue.begin();
bool foundRowHit = false;
while (!foundRowHit && i != writeQueue.end()) {
DRAMPacket* dram_pkt = *i;
- const Bank& bank = dram_pkt->bank_ref;
- if (bank.openRow == dram_pkt->row) { //FR part
+ const Bank& bank = dram_pkt->bankRef;
+ if (bank.openRow == dram_pkt->row) {
DPRINTF(DRAM, "Write row buffer hit\n");
writeQueue.erase(i);
writeQueue.push_front(dram_pkt);
foundRowHit = true;
- } else { //FCFS part
- ;
+ } else {
+ // No row hit, go for first ready
+ if (earliest_banks == 0)
+ earliest_banks = minBankFreeAt(writeQueue);
+
+ // Bank is ready or is one of the first available bank
+ if (bank.freeAt <= curTick() ||
+ bits(earliest_banks, dram_pkt->bankId, dram_pkt->bankId)) {
+ writeQueue.erase(i);
+ writeQueue.push_front(dram_pkt);
+ break;
+ }
}
++i;
}
@@ -822,17 +836,30 @@ SimpleDRAM::chooseNextRead()
// Do nothing, since the request to serve is already the first
// one in the read queue
} else if (memSchedPolicy == Enums::frfcfs) {
+ // Only determine this when needed
+ uint64_t earliest_banks = 0;
+
for (auto i = readQueue.begin(); i != readQueue.end() ; ++i) {
DRAMPacket* dram_pkt = *i;
- const Bank& bank = dram_pkt->bank_ref;
+ const Bank& bank = dram_pkt->bankRef;
// Check if it is a row hit
- if (bank.openRow == dram_pkt->row) { //FR part
+ if (bank.openRow == dram_pkt->row) {
DPRINTF(DRAM, "Row buffer hit\n");
readQueue.erase(i);
readQueue.push_front(dram_pkt);
break;
- } else { //FCFS part
- ;
+ } else {
+ // No row hit, go for first ready
+ if (earliest_banks == 0)
+ earliest_banks = minBankFreeAt(readQueue);
+
+ // Bank is ready or is the first available bank
+ if (bank.freeAt <= curTick() ||
+ bits(earliest_banks, dram_pkt->bankId, dram_pkt->bankId)) {
+ readQueue.erase(i);
+ readQueue.push_front(dram_pkt);
+ break;
+ }
}
}
} else
@@ -887,7 +914,7 @@ SimpleDRAM::estimateLatency(DRAMPacket* dram_pkt, Tick inTime)
Tick bankLat = 0;
rowHitFlag = false;
- const Bank& bank = dram_pkt->bank_ref;
+ const Bank& bank = dram_pkt->bankRef;
if (pageMgmt == Enums::open) { // open-page policy
if (bank.openRow == dram_pkt->row) {
// When we have a row-buffer hit,
@@ -1008,7 +1035,7 @@ SimpleDRAM::doDRAMAccess(DRAMPacket* dram_pkt)
Tick addDelay = (curTick() + accessLat < busBusyUntil) ?
busBusyUntil - (curTick() + accessLat) : 0;
- Bank& bank = dram_pkt->bank_ref;
+ Bank& bank = dram_pkt->bankRef;
// Update bank state
if (pageMgmt == Enums::open) {
@@ -1183,6 +1210,38 @@ SimpleDRAM::maxBankFreeAt() const
return banksFree;
}
+uint64_t
+SimpleDRAM::minBankFreeAt(const deque<DRAMPacket*>& queue) const
+{
+ uint64_t bank_mask = 0;
+ Tick freeAt = MaxTick;
+
+ // detemrine if we have queued transactions targetting the
+ // bank in question
+ vector<bool> got_waiting(ranksPerChannel * banksPerRank, false);
+ for (auto p = queue.begin(); p != queue.end(); ++p) {
+ got_waiting[(*p)->bankId] = true;
+ }
+
+ for (int i = 0; i < ranksPerChannel; i++) {
+ for (int j = 0; j < banksPerRank; j++) {
+ // if we have waiting requests for the bank, and it is
+ // amongst the first available, update the mask
+ if (got_waiting[i * banksPerRank + j] &&
+ banks[i][j].freeAt <= freeAt) {
+ // reset bank mask if new minimum is found
+ if (banks[i][j].freeAt < freeAt)
+ bank_mask = 0;
+ // set the bit corresponding to the available bank
+ uint8_t bit_index = i * ranksPerChannel + j;
+ replaceBits(bank_mask, bit_index, bit_index, 1);
+ freeAt = banks[i][j].freeAt;
+ }
+ }
+ }
+ return bank_mask;
+}
+
void
SimpleDRAM::processRefreshEvent()
{
diff --git a/src/mem/simple_dram.hh b/src/mem/simple_dram.hh
index edba58774..19d23efba 100644
--- a/src/mem/simple_dram.hh
+++ b/src/mem/simple_dram.hh
@@ -39,6 +39,7 @@
*
* Authors: Andreas Hansson
* Ani Udipi
+ * Neha Agarwal
*/
/**
@@ -202,10 +203,17 @@ class SimpleDRAM : public AbstractMemory
/** Will be populated by address decoder */
const uint8_t rank;
- const uint16_t bank;
+ const uint8_t bank;
const uint16_t row;
/**
+ * Bank id is calculated considering banks in all the ranks
+ * eg: 2 ranks each with 8 banks, then bankId = 0 --> rank0, bank0 and
+ * bankId = 8 --> rank1, bank0
+ */
+ const uint16_t bankId;
+
+ /**
* The starting address of the DRAM packet.
* This address could be unaligned to burst size boundaries. The
* reason is to keep the address offset so we can accurately check
@@ -224,14 +232,15 @@ class SimpleDRAM : public AbstractMemory
* If not a split packet (common case), this is set to NULL
*/
BurstHelper* burstHelper;
- Bank& bank_ref;
+ Bank& bankRef;
- DRAMPacket(PacketPtr _pkt, bool _isRead, uint8_t _rank, uint16_t _bank,
- uint16_t _row, Addr _addr, unsigned int _size,
- Bank& _bank_ref)
+ DRAMPacket(PacketPtr _pkt, bool is_read, uint8_t _rank, uint8_t _bank,
+ uint16_t _row, uint16_t bank_id, Addr _addr,
+ unsigned int _size, Bank& bank_ref)
: entryTime(curTick()), readyTime(curTick()),
- pkt(_pkt), isRead(_isRead), rank(_rank), bank(_bank), row(_row),
- addr(_addr), size(_size), burstHelper(NULL), bank_ref(_bank_ref)
+ pkt(_pkt), isRead(is_read), rank(_rank), bank(_bank), row(_row),
+ bankId(bank_id), addr(_addr), size(_size), burstHelper(NULL),
+ bankRef(bank_ref)
{ }
};
@@ -394,6 +403,14 @@ class SimpleDRAM : public AbstractMemory
*/
Tick maxBankFreeAt() const;
+ /**
+ * Find which are the earliest available banks for the enqueued
+ * requests. Assumes maximum of 64 banks per DIMM
+ *
+ * @param Queued requests to consider
+ * @return One-hot encoded mask of bank indices
+ */
+ uint64_t minBankFreeAt(const std::deque<DRAMPacket*>& queue) const;
/**
* Keep track of when row activations happen, in order to enforce