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adding store buffer
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@MayneMei
MayneMei committed Nov 1, 2024
1 parent 83dc12d commit c18dd7b
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Showing 2 changed files with 132 additions and 24 deletions.
140 changes: 116 additions & 24 deletions core/LSU.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,8 @@ namespace olympia
replay_buffer_size_(p->replay_buffer_size),
replay_issue_delay_(p->replay_issue_delay),
ready_queue_(),
store_buffer_("store_buffer", p->ldst_inst_queue_size, getClock()), // Add this line
store_buffer_size_(p->ldst_inst_queue_size),
load_store_info_allocator_(sparta::notNull(OlympiaAllocators::getOlympiaAllocators(node))
->load_store_info_allocator),
memory_access_allocator_(sparta::notNull(OlympiaAllocators::getOlympiaAllocators(node))
Expand Down Expand Up @@ -48,6 +50,7 @@ namespace olympia
ldst_pipeline_.enableCollection(node);
ldst_inst_queue_.enableCollection(node);
replay_buffer_.enableCollection(node);
store_buffer_.enableCollection(node);

// Startup handler for sending initial credits
sparta::StartupEvent(node, CREATE_SPARTA_HANDLER(LSU, sendInitialCredits_));
Expand Down Expand Up @@ -177,6 +180,12 @@ namespace olympia
{
ILOG("New instruction added to the ldst queue " << inst_ptr);
allocateInstToIssueQueue_(inst_ptr);
// allocate to Store buffer
if (inst_ptr->isStoreInst())
{
allocateInstToStoreBuffer_(inst_ptr);
}

handleOperandIssueCheck_(inst_ptr);
lsu_insts_dispatched_++;
}
Expand Down Expand Up @@ -265,7 +274,21 @@ namespace olympia
sparta_assert(inst_ptr->getStatus() == Inst::Status::RETIRED,
"Get ROB Ack, but the store inst hasn't retired yet!");

++stores_retired_;
if (inst_ptr->isStoreInst())
{
auto oldest_store = getOldestStore_();
sparta_assert(oldest_store && oldest_store->getUniqueID() == inst_ptr->getUniqueID(),
"Attempting to retire store out of order! Expected: "
<< (oldest_store ? oldest_store->getUniqueID() : 0)
<< " Got: " << inst_ptr->getUniqueID());

// Remove from store buffer and commit to cache
auto store_info_ptr_ = createLoadStoreInst_(inst_ptr);
store_buffer_.erase(store_buffer_.begin());;
out_cache_lookup_req_.send(store_info_ptr_->getMemoryAccessInfoPtr());
++stores_retired_;
}


updateIssuePriorityAfterStoreInstRetire_(inst_ptr);
if (isReadyToIssueInsts_())
Expand Down Expand Up @@ -592,41 +615,60 @@ namespace olympia
}

const LoadStoreInstInfoPtr & load_store_info_ptr = ldst_pipeline_[cache_read_stage_];
const InstPtr & inst_ptr = load_store_info_ptr->getInstPtr();
const MemoryAccessInfoPtr & mem_access_info_ptr =
load_store_info_ptr->getMemoryAccessInfoPtr();
ILOG(mem_access_info_ptr);

if (false == mem_access_info_ptr->isCacheHit())
{
ILOG("Cannot complete inst, cache miss: " << mem_access_info_ptr);
if (allow_speculative_load_exec_)
if (!inst_ptr->isStoreInst())
{
// for load we check whether we could use store forwarding
// checking whether there are address match in store buffer
uint64_t load_addr = inst_ptr->getTargetVAddr();
auto forwarding_store = findYoungestMatchingStore_(load_addr);

if (forwarding_store)
{
updateInstReplayReady_(load_store_info_ptr);
mem_access_info_ptr->setDataReady(true);
ILOG("Load using forwarded data from store buffer: " << inst_ptr
<< " from store: " << forwarding_store);
}
// There might not be a wake up because the cache cannot handle nay more instruction
// Change to nack wakeup when implemented
if (!load_store_info_ptr->isInReadyQueue())
else
{
appendToReadyQueue_(load_store_info_ptr);
load_store_info_ptr->setState(LoadStoreInstInfo::IssueState::READY);
if (isReadyToIssueInsts_())
if (false == mem_access_info_ptr->isCacheHit())
{
uev_issue_inst_.schedule(sparta::Clock::Cycle(0));
ILOG("Cannot complete inst, cache miss: " << mem_access_info_ptr);
if (allow_speculative_load_exec_)
{
updateInstReplayReady_(load_store_info_ptr);
}
// There might not be a wake up because the cache cannot handle nay more instruction
// Change to nack wakeup when implemented
if (!load_store_info_ptr->isInReadyQueue())
{
appendToReadyQueue_(load_store_info_ptr);
load_store_info_ptr->setState(LoadStoreInstInfo::IssueState::READY);
if (isReadyToIssueInsts_())
{
uev_issue_inst_.schedule(sparta::Clock::Cycle(0));
}
}
ldst_pipeline_.invalidateStage(cache_read_stage_);
return;
}
}
ldst_pipeline_.invalidateStage(cache_read_stage_);
return;
}

if (mem_access_info_ptr->isDataReady())
{
ILOG("Instruction had previously had its data ready");
return;
}
if (mem_access_info_ptr->isDataReady())
{
ILOG("Instruction had previously had its data ready");
return;
}

ILOG("Data ready set for " << mem_access_info_ptr);
mem_access_info_ptr->setDataReady(true);
ILOG("Data ready set for " << mem_access_info_ptr);
mem_access_info_ptr->setDataReady(true);

}
}

if (isReadyToIssueInsts_())
{
ILOG("Cache read issue");
Expand Down Expand Up @@ -790,6 +832,7 @@ namespace olympia
flushIssueQueue_(criteria);
flushReplayBuffer_(criteria);
flushReadyQueue_(criteria);
flushStoreBuffer_(criteria);

// Cancel replay events
auto flush = [&criteria](const LoadStoreInstInfoPtr & ldst_info_ptr) -> bool
Expand Down Expand Up @@ -894,6 +937,40 @@ namespace olympia
ILOG("Append new load/store instruction to issue queue!");
}

void LSU::allocateInstToStoreBuffer_(const InstPtr & inst_ptr)
{
auto store_info_ptr = createLoadStoreInst_(inst_ptr);

sparta_assert(store_buffer_.size() < ldst_inst_queue_size_,
"Appending store buffer causes overflows!");

store_buffer_.push_back(store_info_ptr);
ILOG("Store added to store buffer: " << inst_ptr);
}

InstPtr LSU::findYoungestMatchingStore_(uint64_t addr)
{
InstPtr matching_store = nullptr;

for (auto it = store_buffer_.begin(); it != store_buffer_.end(); ++it)
{
auto & store = *it;
if (store->getTargetVAddr() == addr)
{
matching_store = store;
}
}
return matching_store;
}

InstPtr LSU::getOldestStore_() const
{
if(store_buffer_.empty()) {
return nullptr;
}
return store_buffer_.read(0);
}

bool LSU::allOlderStoresIssued_(const InstPtr & inst_ptr)
{
for (const auto & ldst_info_ptr : ldst_inst_queue_)
Expand Down Expand Up @@ -1368,4 +1445,19 @@ namespace olympia
}
}

void LSU::flushStoreBuffer_(const FlushCriteria & criteria)
{
auto sb_iter = store_buffer_.begin();
while(sb_iter != store_buffer_.end()) {
auto store_ptr = *sb_iter;
if(criteria.includedInFlush(store_ptr)) {
auto delete_iter = sb_iter++;
store_buffer_.erase(delete_iter);
ILOG("Flushed store from store buffer: " << store_ptr);
} else {
++sb_iter;
}
}
}

} // namespace olympia
16 changes: 16 additions & 0 deletions core/LSU.hpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@ namespace olympia
PARAMETER(uint32_t, ldst_inst_queue_size, 8, "LSU ldst inst queue size")
PARAMETER(uint32_t, replay_buffer_size, ldst_inst_queue_size, "Replay buffer size")
PARAMETER(uint32_t, replay_issue_delay, 3, "Replay Issue delay")
PARAMETER(uint32_t, store_buffer_size, ldst_inst_queue_size, "Size of the store buffer")
// LSU microarchitecture parameters
PARAMETER(
bool, allow_speculative_load_exec, true,
Expand Down Expand Up @@ -167,6 +168,10 @@ namespace olympia
using LoadStorePipeline = sparta::Pipeline<LoadStoreInstInfoPtr>;
LoadStorePipeline ldst_pipeline_;

// Store Buffer
sparta::Buffer<InstPtr> store_buffer_;
const uint32_t store_buffer_size_;

// LSU Microarchitecture parameters
const bool allow_speculative_load_exec_;

Expand Down Expand Up @@ -258,6 +263,15 @@ namespace olympia

void allocateInstToIssueQueue_(const InstPtr & inst_ptr);

// allocate store inst to store buffer
void allocateInstToStoreBuffer_(const InstPtr & inst_ptr);

// Search store buffer in FIFO order for youngest matching store
InstPtr findYoungestMatchingStore_(uint64_t addr);

// get oldest store
InstPtr getOldestStore_() const;

bool olderStoresExists_(const InstPtr & inst_ptr);

bool allOlderStoresIssued_(const InstPtr & inst_ptr);
Expand Down Expand Up @@ -315,6 +329,8 @@ namespace olympia
// Flush Replay Buffer
void flushReplayBuffer_(const FlushCriteria &);

void flushStoreBuffer_(const FlushCriteria &);

// Counters
sparta::Counter lsu_insts_dispatched_{getStatisticSet(), "lsu_insts_dispatched",
"Number of LSU instructions dispatched",
Expand Down

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