ruby: fix deadlock bug in banked array resource checks
The Ruby banked array resource checks (initiated from SLICC) did a check and allocate at the same time. If a transition needs more than one resource, then it might check/allocate resource #1, then fail to get resource #2. Another transition might then try to get the same resources, but in reverse order. Deadlock. This patch separates resource checking and resource reservation into two steps to avoid deadlock.
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5 changed files with 36 additions and 10 deletions
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@ -154,7 +154,7 @@ structure (CacheMemory, external = "yes") {
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Cycles getTagLatency();
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Cycles getDataLatency();
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void setMRU(Address);
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void recordRequestType(CacheRequestType);
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void recordRequestType(CacheRequestType, Address);
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bool checkResourceAvailable(CacheResourceType, Address);
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int getCacheSize();
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@ -58,22 +58,36 @@ BankedArray::tryAccess(int64 idx)
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assert(bank < banks);
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if (busyBanks[bank].endAccess >= curTick()) {
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if (!(busyBanks[bank].startAccess == curTick() &&
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busyBanks[bank].idx == idx)) {
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return false;
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} else {
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// We tried to allocate resources twice
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// in the same cycle for the same addr
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}
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return true;
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}
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void
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BankedArray::reserve(int64 idx)
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{
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if (accessLatency == 0)
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return;
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unsigned int bank = mapIndexToBank(idx);
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assert(bank < banks);
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if(busyBanks[bank].endAccess >= curTick()) {
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if (busyBanks[bank].startAccess == curTick() &&
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busyBanks[bank].idx == idx) {
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// this is the same reservation (can happen when
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// e.g., reserve the same resource for read and write)
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return; // OK
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} else {
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panic("BankedArray reservation error");
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}
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}
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busyBanks[bank].idx = idx;
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busyBanks[bank].startAccess = curTick();
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busyBanks[bank].endAccess = curTick() +
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(accessLatency-1) * m_ruby_system->clockPeriod();
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return true;
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}
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unsigned int
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@ -70,6 +70,8 @@ class BankedArray
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// This is so we don't get aliasing on blocks being replaced
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bool tryAccess(int64 idx);
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void reserve(int64 idx);
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Cycles getLatency() const { return accessLatency; }
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};
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@ -528,22 +528,32 @@ CacheMemory::regStats()
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;
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}
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// assumption: SLICC generated files will only call this function
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// once **all** resources are granted
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void
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CacheMemory::recordRequestType(CacheRequestType requestType)
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CacheMemory::recordRequestType(CacheRequestType requestType, Address addr)
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{
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DPRINTF(RubyStats, "Recorded statistic: %s\n",
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CacheRequestType_to_string(requestType));
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switch(requestType) {
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case CacheRequestType_DataArrayRead:
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if (m_resource_stalls)
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dataArray.reserve(addressToCacheSet(addr));
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numDataArrayReads++;
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return;
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case CacheRequestType_DataArrayWrite:
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if (m_resource_stalls)
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dataArray.reserve(addressToCacheSet(addr));
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numDataArrayWrites++;
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return;
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case CacheRequestType_TagArrayRead:
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if (m_resource_stalls)
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tagArray.reserve(addressToCacheSet(addr));
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numTagArrayReads++;
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return;
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case CacheRequestType_TagArrayWrite:
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if (m_resource_stalls)
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tagArray.reserve(addressToCacheSet(addr));
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numTagArrayWrites++;
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return;
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default:
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@ -117,7 +117,7 @@ class CacheMemory : public SimObject
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void regStats();
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bool checkResourceAvailable(CacheResourceType res, Address addr);
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void recordRequestType(CacheRequestType requestType);
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void recordRequestType(CacheRequestType requestType, Address addr);
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public:
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Stats::Scalar m_demand_hits;
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