LLVM  11.0.0git
ResourceManager.h
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1 //===--------------------- ResourceManager.h --------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 /// \file
9 ///
10 /// The classes here represent processor resource units and their management
11 /// strategy. These classes are managed by the Scheduler.
12 ///
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_MCA_RESOURCE_MANAGER_H
16 #define LLVM_MCA_RESOURCE_MANAGER_H
17 
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/MC/MCSchedule.h"
21 #include "llvm/MCA/Instruction.h"
22 #include "llvm/MCA/Support.h"
23 
24 namespace llvm {
25 namespace mca {
26 
27 /// Used to notify the internal state of a processor resource.
28 ///
29 /// A processor resource is available if it is not reserved, and there are
30 /// available slots in the buffer. A processor resource is unavailable if it
31 /// is either reserved, or the associated buffer is full. A processor resource
32 /// with a buffer size of -1 is always available if it is not reserved.
33 ///
34 /// Values of type ResourceStateEvent are returned by method
35 /// ResourceManager::canBeDispatched()
36 ///
37 /// The naming convention for resource state events is:
38 /// * Event names start with prefix RS_
39 /// * Prefix RS_ is followed by a string describing the actual resource state.
44 };
45 
46 /// Resource allocation strategy used by hardware scheduler resources.
48  ResourceStrategy(const ResourceStrategy &) = delete;
49  ResourceStrategy &operator=(const ResourceStrategy &) = delete;
50 
51 public:
53  virtual ~ResourceStrategy();
54 
55  /// Selects a processor resource unit from a ReadyMask.
56  virtual uint64_t select(uint64_t ReadyMask) = 0;
57 
58  /// Called by the ResourceManager when a processor resource group, or a
59  /// processor resource with multiple units has become unavailable.
60  ///
61  /// The default strategy uses this information to bias its selection logic.
62  virtual void used(uint64_t ResourceMask) {}
63 };
64 
65 /// Default resource allocation strategy used by processor resource groups and
66 /// processor resources with multiple units.
68  /// A Mask of resource unit identifiers.
69  ///
70  /// There is one bit set for every available resource unit.
71  /// It defaults to the value of field ResourceSizeMask in ResourceState.
72  const uint64_t ResourceUnitMask;
73 
74  /// A simple round-robin selector for processor resource units.
75  /// Each bit of this mask identifies a sub resource within a group.
76  ///
77  /// As an example, lets assume that this is a default policy for a
78  /// processor resource group composed by the following three units:
79  /// ResourceA -- 0b001
80  /// ResourceB -- 0b010
81  /// ResourceC -- 0b100
82  ///
83  /// Field NextInSequenceMask is used to select the next unit from the set of
84  /// resource units. It defaults to the value of field `ResourceUnitMasks` (in
85  /// this example, it defaults to mask '0b111').
86  ///
87  /// The round-robin selector would firstly select 'ResourceC', then
88  /// 'ResourceB', and eventually 'ResourceA'. When a resource R is used, the
89  /// corresponding bit in NextInSequenceMask is cleared. For example, if
90  /// 'ResourceC' is selected, then the new value of NextInSequenceMask becomes
91  /// 0xb011.
92  ///
93  /// When NextInSequenceMask becomes zero, it is automatically reset to the
94  /// default value (i.e. ResourceUnitMask).
95  uint64_t NextInSequenceMask;
96 
97  /// This field is used to track resource units that are used (i.e. selected)
98  /// by other groups other than the one associated with this strategy object.
99  ///
100  /// In LLVM processor resource groups are allowed to partially (or fully)
101  /// overlap. That means, a same unit may be visible to multiple groups.
102  /// This field keeps track of uses that have originated from outside of
103  /// this group. The idea is to bias the selection strategy, so that resources
104  /// that haven't been used by other groups get prioritized.
105  ///
106  /// The end goal is to (try to) keep the resource distribution as much uniform
107  /// as possible. By construction, this mask only tracks one-level of resource
108  /// usage. Therefore, this strategy is expected to be less accurate when same
109  /// units are used multiple times by other groups within a single round of
110  /// select.
111  ///
112  /// Note: an LRU selector would have a better accuracy at the cost of being
113  /// slightly more expensive (mostly in terms of runtime cost). Methods
114  /// 'select' and 'used', are always in the hot execution path of llvm-mca.
115  /// Therefore, a slow implementation of 'select' would have a negative impact
116  /// on the overall performance of the tool.
117  uint64_t RemovedFromNextInSequence;
118 
119 public:
120  DefaultResourceStrategy(uint64_t UnitMask)
121  : ResourceStrategy(), ResourceUnitMask(UnitMask),
122  NextInSequenceMask(UnitMask), RemovedFromNextInSequence(0) {}
123  virtual ~DefaultResourceStrategy() = default;
124 
125  uint64_t select(uint64_t ReadyMask) override;
126  void used(uint64_t Mask) override;
127 };
128 
129 /// A processor resource descriptor.
130 ///
131 /// There is an instance of this class for every processor resource defined by
132 /// the machine scheduling model.
133 /// Objects of class ResourceState dynamically track the usage of processor
134 /// resource units.
136  /// An index to the MCProcResourceDesc entry in the processor model.
137  const unsigned ProcResourceDescIndex;
138  /// A resource mask. This is generated by the tool with the help of
139  /// function `mca::computeProcResourceMasks' (see Support.h).
140  ///
141  /// Field ResourceMask only has one bit set if this resource state describes a
142  /// processor resource unit (i.e. this is not a group). That means, we can
143  /// quickly check if a resource is a group by simply counting the number of
144  /// bits that are set in the mask.
145  ///
146  /// The most significant bit of a mask (MSB) uniquely identifies a resource.
147  /// Remaining bits are used to describe the composition of a group (Group).
148  ///
149  /// Example (little endian):
150  /// Resource | Mask | MSB | Group
151  /// ---------+------------+------------+------------
152  /// A | 0b000001 | 0b000001 | 0b000000
153  /// | | |
154  /// B | 0b000010 | 0b000010 | 0b000000
155  /// | | |
156  /// C | 0b010000 | 0b010000 | 0b000000
157  /// | | |
158  /// D | 0b110010 | 0b100000 | 0b010010
159  ///
160  /// In this example, resources A, B and C are processor resource units.
161  /// Only resource D is a group resource, and it contains resources B and C.
162  /// That is because MSB(B) and MSB(C) are both contained within Group(D).
163  const uint64_t ResourceMask;
164 
165  /// A ProcResource can have multiple units.
166  ///
167  /// For processor resource groups this field is a mask of contained resource
168  /// units. It is obtained from ResourceMask by clearing the highest set bit.
169  /// The number of resource units in a group can be simply computed as the
170  /// population count of this field.
171  ///
172  /// For normal (i.e. non-group) resources, the number of bits set in this mask
173  /// is equivalent to the number of units declared by the processor model (see
174  /// field 'NumUnits' in 'ProcResourceUnits').
175  uint64_t ResourceSizeMask;
176 
177  /// A mask of ready units.
178  uint64_t ReadyMask;
179 
180  /// Buffered resources will have this field set to a positive number different
181  /// than zero. A buffered resource behaves like a reservation station
182  /// implementing its own buffer for out-of-order execution.
183  ///
184  /// A BufferSize of 1 is used by scheduler resources that force in-order
185  /// execution.
186  ///
187  /// A BufferSize of 0 is used to model in-order issue/dispatch resources.
188  /// Since in-order issue/dispatch resources don't implement buffers, dispatch
189  /// events coincide with issue events.
190  /// Also, no other instruction ca be dispatched/issue while this resource is
191  /// in use. Only when all the "resource cycles" are consumed (after the issue
192  /// event), a new instruction ca be dispatched.
193  const int BufferSize;
194 
195  /// Available slots in the buffer (zero, if this is not a buffered resource).
196  unsigned AvailableSlots;
197 
198  /// This field is set if this resource is currently reserved.
199  ///
200  /// Resources can be reserved for a number of cycles.
201  /// Instructions can still be dispatched to reserved resources. However,
202  /// istructions dispatched to a reserved resource cannot be issued to the
203  /// underlying units (i.e. pipelines) until the resource is released.
204  bool Unavailable;
205 
206  const bool IsAGroup;
207 
208  /// Checks for the availability of unit 'SubResMask' in the group.
209  bool isSubResourceReady(uint64_t SubResMask) const {
210  return ReadyMask & SubResMask;
211  }
212 
213 public:
214  ResourceState(const MCProcResourceDesc &Desc, unsigned Index, uint64_t Mask);
215 
216  unsigned getProcResourceID() const { return ProcResourceDescIndex; }
217  uint64_t getResourceMask() const { return ResourceMask; }
218  uint64_t getReadyMask() const { return ReadyMask; }
219  int getBufferSize() const { return BufferSize; }
220 
221  bool isBuffered() const { return BufferSize > 0; }
222  bool isInOrder() const { return BufferSize == 1; }
223 
224  /// Returns true if this is an in-order dispatch/issue resource.
225  bool isADispatchHazard() const { return BufferSize == 0; }
226  bool isReserved() const { return Unavailable; }
227 
228  void setReserved() { Unavailable = true; }
229  void clearReserved() { Unavailable = false; }
230 
231  /// Returs true if this resource is not reserved, and if there are at least
232  /// `NumUnits` available units.
233  bool isReady(unsigned NumUnits = 1) const;
234 
235  bool isAResourceGroup() const { return IsAGroup; }
236 
237  bool containsResource(uint64_t ID) const { return ResourceMask & ID; }
238 
239  void markSubResourceAsUsed(uint64_t ID) {
240  assert(isSubResourceReady(ID));
241  ReadyMask ^= ID;
242  }
243 
244  void releaseSubResource(uint64_t ID) {
245  assert(!isSubResourceReady(ID));
246  ReadyMask ^= ID;
247  }
248 
249  unsigned getNumUnits() const {
250  return isAResourceGroup() ? 1U : countPopulation(ResourceSizeMask);
251  }
252 
253  /// Checks if there is an available slot in the resource buffer.
254  ///
255  /// Returns RS_BUFFER_AVAILABLE if this is not a buffered resource, or if
256  /// there is a slot available.
257  ///
258  /// Returns RS_RESERVED if this buffered resource is a dispatch hazard, and it
259  /// is reserved.
260  ///
261  /// Returns RS_BUFFER_UNAVAILABLE if there are no available slots.
262  ResourceStateEvent isBufferAvailable() const;
263 
264  /// Reserve a buffer slot.
265  ///
266  /// Returns true if the buffer is not full.
267  /// It always returns true if BufferSize is set to zero.
268  bool reserveBuffer() {
269  if (BufferSize <= 0)
270  return true;
271 
272  --AvailableSlots;
273  assert(AvailableSlots <= static_cast<unsigned>(BufferSize));
274  return AvailableSlots;
275  }
276 
277  /// Releases a slot in the buffer.
278  void releaseBuffer() {
279  // Ignore dispatch hazards or invalid buffer sizes.
280  if (BufferSize <= 0)
281  return;
282 
283  ++AvailableSlots;
284  assert(AvailableSlots <= static_cast<unsigned>(BufferSize));
285  }
286 
287 #ifndef NDEBUG
288  void dump() const;
289 #endif
290 };
291 
292 /// A resource unit identifier.
293 ///
294 /// This is used to identify a specific processor resource unit using a pair
295 /// of indices where the 'first' index is a processor resource mask, and the
296 /// 'second' index is an index for a "sub-resource" (i.e. unit).
297 typedef std::pair<uint64_t, uint64_t> ResourceRef;
298 
299 // First: a MCProcResourceDesc index identifying a buffered resource.
300 // Second: max number of buffer entries used in this resource.
301 typedef std::pair<unsigned, unsigned> BufferUsageEntry;
302 
303 /// A resource manager for processor resource units and groups.
304 ///
305 /// This class owns all the ResourceState objects, and it is responsible for
306 /// acting on requests from a Scheduler by updating the internal state of
307 /// ResourceState objects.
308 /// This class doesn't know about instruction itineraries and functional units.
309 /// In future, it can be extended to support itineraries too through the same
310 /// public interface.
312  // Set of resources available on the subtarget.
313  //
314  // There is an instance of ResourceState for every resource declared by the
315  // target scheduling model.
316  //
317  // Elements of this vector are ordered by resource kind. In particular,
318  // resource units take precedence over resource groups.
319  //
320  // The index of a processor resource in this vector depends on the value of
321  // its mask (see the description of field ResourceState::ResourceMask). In
322  // particular, it is computed as the position of the most significant bit set
323  // (MSB) in the mask plus one (since we want to ignore the invalid resource
324  // descriptor at index zero).
325  //
326  // Example (little endian):
327  //
328  // Resource | Mask | MSB | Index
329  // ---------+---------+---------+-------
330  // A | 0b00001 | 0b00001 | 1
331  // | | |
332  // B | 0b00100 | 0b00100 | 3
333  // | | |
334  // C | 0b10010 | 0b10000 | 5
335  //
336  //
337  // The same index is also used to address elements within vector `Strategies`
338  // and vector `Resource2Groups`.
339  std::vector<std::unique_ptr<ResourceState>> Resources;
340  std::vector<std::unique_ptr<ResourceStrategy>> Strategies;
341 
342  // Used to quickly identify groups that own a particular resource unit.
343  std::vector<uint64_t> Resource2Groups;
344 
345  // A table that maps processor resource IDs to processor resource masks.
346  SmallVector<uint64_t, 8> ProcResID2Mask;
347 
348  // A table that maps resource indices to actual processor resource IDs in the
349  // scheduling model.
350  SmallVector<unsigned, 8> ResIndex2ProcResID;
351 
352  // Keeps track of which resources are busy, and how many cycles are left
353  // before those become usable again.
355 
356  // Set of processor resource units available on the target.
357  uint64_t ProcResUnitMask;
358 
359  // Set of processor resource units that are available during this cycle.
360  uint64_t AvailableProcResUnits;
361 
362  // Set of processor resources that are currently reserved.
363  uint64_t ReservedResourceGroups;
364 
365  // Set of unavailable scheduler buffer resources. This is used internally to
366  // speedup `canBeDispatched()` queries.
367  uint64_t AvailableBuffers;
368 
369  // Set of dispatch hazard buffer resources that are currently unavailable.
370  uint64_t ReservedBuffers;
371 
372  // Returns the actual resource unit that will be used.
373  ResourceRef selectPipe(uint64_t ResourceID);
374 
375  void use(const ResourceRef &RR);
376  void release(const ResourceRef &RR);
377 
378  unsigned getNumUnits(uint64_t ResourceID) const;
379 
380  // Overrides the selection strategy for the processor resource with the given
381  // mask.
382  void setCustomStrategyImpl(std::unique_ptr<ResourceStrategy> S,
383  uint64_t ResourceMask);
384 
385 public:
386  ResourceManager(const MCSchedModel &SM);
387  virtual ~ResourceManager() = default;
388 
389  // Overrides the selection strategy for the resource at index ResourceID in
390  // the MCProcResourceDesc table.
391  void setCustomStrategy(std::unique_ptr<ResourceStrategy> S,
392  unsigned ResourceID) {
393  assert(ResourceID < ProcResID2Mask.size() &&
394  "Invalid resource index in input!");
395  return setCustomStrategyImpl(std::move(S), ProcResID2Mask[ResourceID]);
396  }
397 
398  // Returns RS_BUFFER_AVAILABLE if buffered resources are not reserved, and if
399  // there are enough available slots in the buffers.
400  ResourceStateEvent canBeDispatched(uint64_t ConsumedBuffers) const;
401 
402  // Return the processor resource identifier associated to this Mask.
403  unsigned resolveResourceMask(uint64_t Mask) const;
404 
405  // Acquires a slot from every buffered resource in mask `ConsumedBuffers`.
406  // Units that are dispatch hazards (i.e. BufferSize=0) are marked as reserved.
407  void reserveBuffers(uint64_t ConsumedBuffers);
408 
409  // Releases a slot from every buffered resource in mask `ConsumedBuffers`.
410  // ConsumedBuffers is a bitmask of previously acquired buffers (using method
411  // `reserveBuffers`). Units that are dispatch hazards (i.e. BufferSize=0) are
412  // not automatically unreserved by this method.
413  void releaseBuffers(uint64_t ConsumedBuffers);
414 
415  // Reserve a processor resource. A reserved resource is not available for
416  // instruction issue until it is released.
417  void reserveResource(uint64_t ResourceID);
418 
419  // Release a previously reserved processor resource.
420  void releaseResource(uint64_t ResourceID);
421 
422  // Returns a zero mask if resources requested by Desc are all available during
423  // this cycle. It returns a non-zero mask value only if there are unavailable
424  // processor resources; each bit set in the mask represents a busy processor
425  // resource unit or a reserved processor resource group.
426  uint64_t checkAvailability(const InstrDesc &Desc) const;
427 
428  uint64_t getProcResUnitMask() const { return ProcResUnitMask; }
429  uint64_t getAvailableProcResUnits() const { return AvailableProcResUnits; }
430 
431  void issueInstruction(
432  const InstrDesc &Desc,
433  SmallVectorImpl<std::pair<ResourceRef, ResourceCycles>> &Pipes);
434 
435  void cycleEvent(SmallVectorImpl<ResourceRef> &ResourcesFreed);
436 
437 #ifndef NDEBUG
438  void dump() const {
439  for (const std::unique_ptr<ResourceState> &Resource : Resources)
440  Resource->dump();
441  }
442 #endif
443 };
444 } // namespace mca
445 } // namespace llvm
446 
447 #endif // LLVM_MCA_RESOURCE_MANAGER_H
A resource manager for processor resource units and groups.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
void setCustomStrategy(std::unique_ptr< ResourceStrategy > S, unsigned ResourceID)
void markSubResourceAsUsed(uint64_t ID)
bool containsResource(uint64_t ID) const
virtual void used(uint64_t ResourceMask)
Called by the ResourceManager when a processor resource group, or a processor resource with multiple ...
uint64_t getResourceMask() const
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:43
std::underlying_type_t< E > Mask()
Get a bitmask with 1s in all places up to the high-order bit of E&#39;s largest value.
Definition: BitmaskEnum.h:80
virtual uint64_t select(uint64_t ReadyMask)=0
Selects a processor resource unit from a ReadyMask.
unsigned getNumUnits() const
uint64_t getReadyMask() const
void dump(const SparseBitVector< ElementSize > &LHS, raw_ostream &out)
Move duplicate certain instructions close to their use
Definition: Localizer.cpp:29
void releaseBuffer()
Releases a slot in the buffer.
std::pair< uint64_t, uint64_t > ResourceRef
A resource unit identifier.
bool isADispatchHazard() const
Returns true if this is an in-order dispatch/issue resource.
Helper functions used by various pipeline components.
ResourceStateEvent
Used to notify the internal state of a processor resource.
unsigned countPopulation(T Value)
Count the number of set bits in a value.
Definition: MathExtras.h:568
uint64_t getAvailableProcResUnits() const
Define a kind of processor resource that will be modeled by the scheduler.
Definition: MCSchedule.h:32
std::pair< unsigned, unsigned > BufferUsageEntry
An instruction descriptor.
Definition: Instruction.h:348
A processor resource descriptor.
bool reserveBuffer()
Reserve a buffer slot.
This file defines abstractions used by the Pipeline to model register reads, register writes and inst...
void releaseSubResource(uint64_t ID)
size_t size() const
Definition: SmallVector.h:66
DefaultResourceStrategy(uint64_t UnitMask)
unsigned getProcResourceID() const
Default resource allocation strategy used by processor resource groups and processor resources with m...
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
Resource allocation strategy used by hardware scheduler resources.
Machine model for scheduling, bundling, and heuristics.
Definition: MCSchedule.h:244
uint64_t getProcResUnitMask() const