gem5  v21.2.1.1
TBEStorage.hh
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37 
38 #ifndef __MEM_RUBY_STRUCTURES_TBESTORAGE_HH__
39 #define __MEM_RUBY_STRUCTURES_TBESTORAGE_HH__
40 
41 #include <cassert>
42 #include <stack>
43 #include <unordered_map>
44 
45 #include <base/statistics.hh>
46 
47 namespace gem5
48 {
49 
50 namespace ruby
51 {
52 
53 // The TBEStorage is used to track the resources consumed by the TBETable,
54 // i.e. the number of available TBE slots.
55 //
56 // TBEStorage resource tracking has two main differences from TBETable:
57 //
58 // 1) Allows slot reservation. This is useful to implement protocols that
59 // employ retry/credit messages instead of stall when the controller runs
60 // out of TBEs to accept new request.
61 //
62 // 2) Can also assign multiple entries to the same slot. This is useful to
63 // more easily model cases where multiple transactions share the same TBE
64 // resource (i.e. the slot).
65 // E.g: a request that triggers a replacement in a system without
66 // dedicated WB/Eviction buffer; both transactions can can have separate
67 // logical TBEs associated to the same slot.
68 //
69 // The motivation for having a separate structures for tracking TBEs
70 // availability are twofold:
71 //
72 // - Keeps TBETable simple and without the additional overhead for
73 // protocols that do not need these additional features.
74 //
75 // - Having two separate transactions sharing the same TBE resource using
76 // the current TBETable would be cumbersome since the TBETable is indexed
77 // by the transaction address.
78 
80 {
81  public:
82  TBEStorage(statistics::Group *parent, int number_of_TBEs);
83 
84  // Returns the current number of slots allocated
85  int size() const { return m_slots_used.size(); }
86 
87  // Returns the total capacity of this TBEStorage table
88  int capacity() const { return m_slots_used.size() + m_slots_avail.size(); }
89 
90  // Returns number of slots currently reserved
91  int reserved() const { return m_reserved; }
92 
93  // Returns the number of slots available
94  int slotsAvailable() const { return m_slots_avail.size() - m_reserved; }
95 
96  // Returns the TBEStorage utilization
97  float utilization() const { return size() / (float)capacity(); }
98 
99  // Returns true if slotsAvailable() >= n; current_time is always ignored
100  // This allows this class to be used with check_allocate in SLICC to
101  // trigger resource stalls when there are no slots available
102  bool areNSlotsAvailable(int n, Tick current_time = 0) const;
103 
104  // Increase/decrease the number of reserved slots. Having reserved slots
105  // reduces the number of slots available for allocation
106  void incrementReserved();
107  void decrementReserved();
108 
109  // Assign a TBETable entry to a free slot and returns the slot number.
110  // Notice we don't need any info from TBETable and just track the number
111  // of entries assigned to each slot.
112  // This funcion requires slotsAvailable() > 0
113  int addEntryToNewSlot();
114 
115  // Assign an entry to an existing non-empty slot
116  void addEntryToSlot(int slot);
117 
118  // Remove an entry from an existing non-empty slot. The slot becomes
119  // available again when the number of assigned entries == 0
120  void removeEntryFromSlot(int slot);
121 
122  private:
124  std::stack<int> m_slots_avail;
125  std::unordered_map<int, int> m_slots_used;
126 
128  {
130 
131  // Statistical variables
135  } m_stats;
136 };
137 
138 inline bool
139 TBEStorage::areNSlotsAvailable(int n, Tick current_time) const
140 {
141  return slotsAvailable() >= n;
142 }
143 
144 inline void
146 {
147  ++m_reserved;
149 }
150 
151 inline void
153 {
154  assert(m_reserved > 0);
155  --m_reserved;
157 }
158 
159 inline int
161 {
162  assert(slotsAvailable() > 0);
163  assert(m_slots_avail.size() > 0);
164  int slot = m_slots_avail.top();
165  m_slots_used[slot] = 1;
166  m_slots_avail.pop();
167  m_stats.avg_size = size();
169  return slot;
170 }
171 
172 inline void
174 {
175  auto iter = m_slots_used.find(slot);
176  assert(iter != m_slots_used.end());
177  iter->second += 1;
178 }
179 
180 inline void
182 {
183  auto iter = m_slots_used.find(slot);
184  assert(iter != m_slots_used.end());
185  assert(iter->second > 0);
186  iter->second -= 1;
187  if (iter->second == 0) {
188  m_slots_used.erase(iter);
189  m_slots_avail.push(slot);
190  }
191  m_stats.avg_size = size();
193 }
194 
195 } // namespace ruby
196 } // namespace gem5
197 
198 #endif
gem5::ruby::TBEStorage::m_reserved
int m_reserved
Definition: TBEStorage.hh:123
gem5::ruby::TBEStorage::TBEStorage
TBEStorage(statistics::Group *parent, int number_of_TBEs)
Definition: TBEStorage.cc:46
gem5::ruby::TBEStorage::slotsAvailable
int slotsAvailable() const
Definition: TBEStorage.hh:94
gem5::statistics::Average
A stat that calculates the per tick average of a value.
Definition: statistics.hh:1958
gem5::ruby::TBEStorage::areNSlotsAvailable
bool areNSlotsAvailable(int n, Tick current_time=0) const
Definition: TBEStorage.hh:139
gem5::ruby::TBEStorage::incrementReserved
void incrementReserved()
Definition: TBEStorage.hh:145
gem5::ruby::TBEStorage::reserved
int reserved() const
Definition: TBEStorage.hh:91
statistics.hh
gem5::ruby::TBEStorage::utilization
float utilization() const
Definition: TBEStorage.hh:97
gem5::Tick
uint64_t Tick
Tick count type.
Definition: types.hh:58
gem5::ruby::TBEStorage::TBEStorageStats::avg_util
statistics::Average avg_util
Definition: TBEStorage.hh:133
gem5::ruby::TBEStorage::addEntryToNewSlot
int addEntryToNewSlot()
Definition: TBEStorage.hh:160
gem5::ruby::TBEStorage::removeEntryFromSlot
void removeEntryFromSlot(int slot)
Definition: TBEStorage.hh:181
gem5::ruby::TBEStorage::TBEStorageStats::avg_reserved
statistics::Average avg_reserved
Definition: TBEStorage.hh:134
gem5::ruby::TBEStorage::capacity
int capacity() const
Definition: TBEStorage.hh:88
gem5::ArmISA::n
Bitfield< 31 > n
Definition: misc_types.hh:456
gem5::ruby::TBEStorage::addEntryToSlot
void addEntryToSlot(int slot)
Definition: TBEStorage.hh:173
gem5::ruby::TBEStorage::TBEStorageStats
Definition: TBEStorage.hh:127
gem5::ruby::TBEStorage::decrementReserved
void decrementReserved()
Definition: TBEStorage.hh:152
gem5::statistics::Group
Statistics container.
Definition: group.hh:93
gem5::ruby::TBEStorage
Definition: TBEStorage.hh:79
gem5::ruby::TBEStorage::TBEStorageStats::TBEStorageStats
TBEStorageStats(statistics::Group *parent)
Definition: TBEStorage.cc:53
gem5::ruby::TBEStorage::m_slots_used
std::unordered_map< int, int > m_slots_used
Definition: TBEStorage.hh:125
gem5
Reference material can be found at the JEDEC website: UFS standard http://www.jedec....
Definition: tlb.cc:60
gem5::ruby::TBEStorage::m_slots_avail
std::stack< int > m_slots_avail
Definition: TBEStorage.hh:124
gem5::ruby::TBEStorage::size
int size() const
Definition: TBEStorage.hh:85
gem5::ruby::TBEStorage::TBEStorageStats::avg_size
statistics::Average avg_size
Definition: TBEStorage.hh:132
gem5::ruby::TBEStorage::m_stats
gem5::ruby::TBEStorage::TBEStorageStats m_stats

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