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/*
* Copyright (c) 2012, 2017 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* Copyright (c) 2013 Advanced Micro Devices, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#ifndef __CPU_O3_RENAME_HH__
#define __CPU_O3_RENAME_HH__
#include <list>
#include <utility>
#include "base/statistics.hh"
#include "cpu/o3/comm.hh"
#include "cpu/o3/commit.hh"
#include "cpu/o3/dyn_inst_ptr.hh"
#include "cpu/o3/free_list.hh"
#include "cpu/o3/iew.hh"
#include "cpu/o3/limits.hh"
#include "cpu/timebuf.hh"
#include "sim/probe/probe.hh"
namespace gem5
{
struct BaseO3CPUParams;
namespace o3
{
/**
* Rename handles both single threaded and SMT rename. Its
* width is specified by the parameters; each cycle it tries to rename
* that many instructions. It holds onto the rename history of all
* instructions with destination registers, storing the
* arch. register, the new physical register, and the old physical
* register, to allow for undoing of mappings if squashing happens, or
* freeing up registers upon commit. Rename handles blocking if the
* ROB, IQ, or LSQ is going to be full. Rename also handles barriers,
* and does so by stalling on the instruction until the ROB is empty
* and there are no instructions in flight to the ROB.
*/
class Rename
{
public:
// A deque is used to queue the instructions. Barrier insts must
// be added to the front of the queue, which is the only reason for
// using a deque instead of a queue. (Most other stages use a
// queue)
typedef std::deque<DynInstPtr> InstQueue;
public:
/** Overall rename status. Used to determine if the CPU can
* deschedule itself due to a lack of activity.
*/
enum RenameStatus
{
Active,
Inactive
};
/** Individual thread status. */
enum ThreadStatus
{
Running,
Idle,
StartSquash,
Squashing,
Blocked,
Unblocking,
SerializeStall
};
private:
/** Rename status. */
RenameStatus _status;
/** Per-thread status. */
ThreadStatus renameStatus[MaxThreads];
/** Probe points. */
typedef std::pair<InstSeqNum, PhysRegIdPtr> SeqNumRegPair;
/** To probe when register renaming for an instruction is complete */
ProbePointArg<DynInstPtr> *ppRename;
/**
* To probe when an instruction is squashed and the register mapping
* for it needs to be undone
*/
ProbePointArg<SeqNumRegPair> *ppSquashInRename;
public:
/** Rename constructor. */
Rename(CPU *_cpu, const BaseO3CPUParams &params);
/** Returns the name of rename. */
std::string name() const;
/** Registers probes. */
void regProbePoints();
/** Sets the main backwards communication time buffer pointer. */
void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr);
/** Sets pointer to time buffer used to communicate to the next stage. */
void setRenameQueue(TimeBuffer<RenameStruct> *rq_ptr);
/** Sets pointer to time buffer coming from decode. */
void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr);
/** Sets pointer to IEW stage. Used only for initialization. */
void setIEWStage(IEW *iew_stage) { iew_ptr = iew_stage; }
/** Sets pointer to commit stage. Used only for initialization. */
void
setCommitStage(Commit *commit_stage)
{
commit_ptr = commit_stage;
}
private:
/** Pointer to IEW stage. Used only for initialization. */
IEW *iew_ptr;
/** Pointer to commit stage. Used only for initialization. */
Commit *commit_ptr;
public:
/** Initializes variables for the stage. */
void startupStage();
/** Clear all thread-specific states */
void clearStates(ThreadID tid);
/** Sets pointer to list of active threads. */
void setActiveThreads(std::list<ThreadID> *at_ptr);
/** Sets pointer to rename maps (per-thread structures). */
void setRenameMap(UnifiedRenameMap rm_ptr[MaxThreads]);
/** Sets pointer to the free list. */
void setFreeList(UnifiedFreeList *fl_ptr);
/** Sets pointer to the scoreboard. */
void setScoreboard(Scoreboard *_scoreboard);
/** Perform sanity checks after a drain. */
void drainSanityCheck() const;
/** Has the stage drained? */
bool isDrained() const;
/** Takes over from another CPU's thread. */
void takeOverFrom();
/** Squashes all instructions in a thread. */
void squash(const InstSeqNum &squash_seq_num, ThreadID tid);
/** Ticks rename, which processes all input signals and attempts to rename
* as many instructions as possible.
*/
void tick();
/** Debugging function used to dump history buffer of renamings. */
void dumpHistory();
private:
/** Reset this pipeline stage */
void resetStage();
/** Determines what to do based on rename's current status.
* @param status_change rename() sets this variable if there was a status
* change (ie switching from blocking to unblocking).
* @param tid Thread id to rename instructions from.
*/
void rename(bool &status_change, ThreadID tid);
/** Renames instructions for the given thread. Also handles serializing
* instructions.
*/
void renameInsts(ThreadID tid);
/** Inserts unused instructions from a given thread into the skid buffer,
* to be renamed once rename unblocks.
*/
void skidInsert(ThreadID tid);
/** Separates instructions from decode into individual lists of instructions
* sorted by thread.
*/
void sortInsts();
/** Returns if all of the skid buffers are empty. */
bool skidsEmpty();
/** Updates overall rename status based on all of the threads' statuses. */
void updateStatus();
/** Switches rename to blocking, and signals back that rename has become
* blocked.
* @return Returns true if there is a status change.
*/
bool block(ThreadID tid);
/** Switches rename to unblocking if the skid buffer is empty, and signals
* back that rename has unblocked.
* @return Returns true if there is a status change.
*/
bool unblock(ThreadID tid);
/** Executes actual squash, removing squashed instructions. */
void doSquash(const InstSeqNum &squash_seq_num, ThreadID tid);
/** Removes a committed instruction's rename history. */
void removeFromHistory(InstSeqNum inst_seq_num, ThreadID tid);
/** Renames the source registers of an instruction. */
void renameSrcRegs(const DynInstPtr &inst, ThreadID tid);
/** Renames the destination registers of an instruction. */
void renameDestRegs(const DynInstPtr &inst, ThreadID tid);
/** Calculates the number of free ROB entries for a specific thread. */
int calcFreeROBEntries(ThreadID tid);
/** Calculates the number of free IQ entries for a specific thread. */
int calcFreeIQEntries(ThreadID tid);
/** Calculates the number of free LQ entries for a specific thread. */
int calcFreeLQEntries(ThreadID tid);
/** Calculates the number of free SQ entries for a specific thread. */
int calcFreeSQEntries(ThreadID tid);
/** Returns the number of valid instructions coming from decode. */
unsigned validInsts();
/** Reads signals telling rename to block/unblock. */
void readStallSignals(ThreadID tid);
/** Checks if any stages are telling rename to block. */
bool checkStall(ThreadID tid);
/** Gets the number of free entries for a specific thread. */
void readFreeEntries(ThreadID tid);
/** Checks the signals and updates the status. */
bool checkSignalsAndUpdate(ThreadID tid);
/** Either serializes on the next instruction available in the InstQueue,
* or records that it must serialize on the next instruction to enter
* rename.
* @param inst_list The list of younger, unprocessed instructions for the
* thread that has the serializeAfter instruction.
* @param tid The thread id.
*/
void serializeAfter(InstQueue &inst_list, ThreadID tid);
/** Holds the information for each destination register rename. It holds
* the instruction's sequence number, the arch register, the old physical
* register for that arch. register, and the new physical register.
*/
struct RenameHistory
{
RenameHistory(InstSeqNum _instSeqNum, const RegId& _archReg,
PhysRegIdPtr _newPhysReg,
PhysRegIdPtr _prevPhysReg)
: instSeqNum(_instSeqNum), archReg(_archReg),
newPhysReg(_newPhysReg), prevPhysReg(_prevPhysReg)
{
}
/** The sequence number of the instruction that renamed. */
InstSeqNum instSeqNum;
/** The architectural register index that was renamed. */
RegId archReg;
/** The new physical register that the arch. register is renamed to. */
PhysRegIdPtr newPhysReg;
/** The old physical register that the arch. register was renamed to.
*/
PhysRegIdPtr prevPhysReg;
};
/** A per-thread list of all destination register renames, used to either
* undo rename mappings or free old physical registers.
*/
std::list<RenameHistory> historyBuffer[MaxThreads];
/** Pointer to CPU. */
CPU *cpu;
/** Pointer to main time buffer used for backwards communication. */
TimeBuffer<TimeStruct> *timeBuffer;
/** Wire to get IEW's output from backwards time buffer. */
TimeBuffer<TimeStruct>::wire fromIEW;
/** Wire to get commit's output from backwards time buffer. */
TimeBuffer<TimeStruct>::wire fromCommit;
/** Wire to write infromation heading to previous stages. */
TimeBuffer<TimeStruct>::wire toDecode;
/** Rename instruction queue. */
TimeBuffer<RenameStruct> *renameQueue;
/** Wire to write any information heading to IEW. */
TimeBuffer<RenameStruct>::wire toIEW;
/** Decode instruction queue interface. */
TimeBuffer<DecodeStruct> *decodeQueue;
/** Wire to get decode's output from decode queue. */
TimeBuffer<DecodeStruct>::wire fromDecode;
/** Queue of all instructions coming from decode this cycle. */
InstQueue insts[MaxThreads];
/** Skid buffer between rename and decode. */
InstQueue skidBuffer[MaxThreads];
/** Rename map interface. */
UnifiedRenameMap *renameMap[MaxThreads];
/** Free list interface. */
UnifiedFreeList *freeList;
/** Pointer to the list of active threads. */
std::list<ThreadID> *activeThreads;
/** Pointer to the scoreboard. */
Scoreboard *scoreboard;
/** Count of instructions in progress that have been sent off to the IQ
* and ROB, but are not yet included in their occupancy counts.
*/
int instsInProgress[MaxThreads];
/** Count of Load instructions in progress that have been sent off to the
* IQ and ROB, but are not yet included in their occupancy counts.
*/
int loadsInProgress[MaxThreads];
/** Count of Store instructions in progress that have been sent off to the
* IQ and ROB, but are not yet included in their occupancy counts.
*/
int storesInProgress[MaxThreads];
/** Variable that tracks if decode has written to the time buffer this
* cycle. Used to tell CPU if there is activity this cycle.
*/
bool wroteToTimeBuffer;
/** Structures whose free entries impact the amount of instructions that
* can be renamed.
*/
struct FreeEntries
{
unsigned iqEntries;
unsigned robEntries;
unsigned lqEntries;
unsigned sqEntries;
};
/** Per-thread tracking of the number of free entries of back-end
* structures.
*/
FreeEntries freeEntries[MaxThreads];
/** Records if the ROB is empty. In SMT mode the ROB may be dynamically
* partitioned between threads, so the ROB must tell rename when it is
* empty.
*/
bool emptyROB[MaxThreads];
/** Source of possible stalls. */
struct Stalls
{
bool iew;
bool commit;
};
/** Tracks which stages are telling decode to stall. */
Stalls stalls[MaxThreads];
/** The serialize instruction that rename has stalled on. */
DynInstPtr serializeInst[MaxThreads];
/** Records if rename needs to serialize on the next instruction for any
* thread.
*/
bool serializeOnNextInst[MaxThreads];
/** Delay between iew and rename, in ticks. */
int iewToRenameDelay;
/** Delay between decode and rename, in ticks. */
int decodeToRenameDelay;
/** Delay between commit and rename, in ticks. */
unsigned commitToRenameDelay;
/** Rename width, in instructions. */
unsigned renameWidth;
/** The index of the instruction in the time buffer to IEW that rename is
* currently using.
*/
unsigned toIEWIndex;
/** Whether or not rename needs to block this cycle. */
bool blockThisCycle;
/** Whether or not rename needs to resume a serialize instruction
* after squashing. */
bool resumeSerialize;
/** Whether or not rename needs to resume clearing out the skidbuffer
* after squashing. */
bool resumeUnblocking;
/** The number of threads active in rename. */
ThreadID numThreads;
/** The maximum skid buffer size. */
unsigned skidBufferMax;
/** Enum to record the source of a structure full stall. Can come from
* either ROB, IQ, LSQ, and it is priortized in that order.
*/
enum FullSource
{
ROB,
IQ,
LQ,
SQ,
NONE
};
/** Function used to increment the stat that corresponds to the source of
* the stall.
*/
void incrFullStat(const FullSource &source);
struct RenameStats : public statistics::Group
{
RenameStats(statistics::Group *parent);
/** Stat for total number of cycles spent squashing. */
statistics::Scalar squashCycles;
/** Stat for total number of cycles spent idle. */
statistics::Scalar idleCycles;
/** Stat for total number of cycles spent blocking. */
statistics::Scalar blockCycles;
/** Stat for total number of cycles spent stalling for a serializing
* inst. */
statistics::Scalar serializeStallCycles;
/** Stat for total number of cycles spent running normally. */
statistics::Scalar runCycles;
/** Stat for total number of cycles spent unblocking. */
statistics::Scalar unblockCycles;
/** Stat for total number of renamed instructions. */
statistics::Scalar renamedInsts;
/** Stat for total number of squashed instructions that rename
* discards. */
statistics::Scalar squashedInsts;
/** Stat for total number of times that the ROB starts a stall in
* rename. */
statistics::Scalar ROBFullEvents;
/** Stat for total number of times that the IQ starts a stall in
* rename. */
statistics::Scalar IQFullEvents;
/** Stat for total number of times that the LQ starts a stall in
* rename. */
statistics::Scalar LQFullEvents;
/** Stat for total number of times that the SQ starts a stall in
* rename. */
statistics::Scalar SQFullEvents;
/** Stat for total number of times that rename runs out of free
* registers to use to rename. */
statistics::Scalar fullRegistersEvents;
/** Stat for total number of renamed destination registers. */
statistics::Scalar renamedOperands;
/** Stat for total number of source register rename lookups. */
statistics::Scalar lookups;
statistics::Scalar intLookups;
statistics::Scalar fpLookups;
statistics::Scalar vecLookups;
statistics::Scalar vecPredLookups;
/** Stat for total number of committed renaming mappings. */
statistics::Scalar committedMaps;
/** Stat for total number of mappings that were undone due to a
* squash. */
statistics::Scalar undoneMaps;
/** Number of serialize instructions handled. */
statistics::Scalar serializing;
/** Number of instructions marked as temporarily serializing. */
statistics::Scalar tempSerializing;
/** Number of instructions inserted into skid buffers. */
statistics::Scalar skidInsts;
} stats;
};
} // namespace o3
} // namespace gem5
#endif // __CPU_O3_RENAME_HH__