gem5/cpu/o3/fetch.hh
Kevin Lim e3d5588ca7 O3 code update/cleanup.
cpu/o3/commit_impl.hh:
    O3 code update/cleanup.  Fetch fault code no longer needed (see previous checkin).

--HG--
extra : convert_revision : f602e7f978e19b8900dce482f38f9c7a195e94da
2006-05-19 15:53:17 -04:00

411 lines
12 KiB
C++

/*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* 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,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef __CPU_O3_FETCH_HH__
#define __CPU_O3_FETCH_HH__
#include "base/statistics.hh"
#include "base/timebuf.hh"
#include "cpu/pc_event.hh"
#include "mem/mem_interface.hh"
#include "sim/eventq.hh"
class Sampler;
/**
* DefaultFetch class handles both single threaded and SMT fetch. Its
* width is specified by the parameters; each cycle it tries to fetch
* that many instructions. It supports using a branch predictor to
* predict direction and targets.
* It supports the idling functionalitiy of the CPU by indicating to
* the CPU when it is active and inactive.
*/
template <class Impl>
class DefaultFetch
{
public:
/** Typedefs from Impl. */
typedef typename Impl::CPUPol CPUPol;
typedef typename Impl::DynInst DynInst;
typedef typename Impl::DynInstPtr DynInstPtr;
typedef typename Impl::FullCPU FullCPU;
typedef typename Impl::Params Params;
/** Typedefs from the CPU policy. */
typedef typename CPUPol::BPredUnit BPredUnit;
typedef typename CPUPol::FetchStruct FetchStruct;
typedef typename CPUPol::TimeStruct TimeStruct;
/** Typedefs from ISA. */
typedef TheISA::MachInst MachInst;
typedef TheISA::ExtMachInst ExtMachInst;
public:
/** Overall fetch status. Used to determine if the CPU can
* deschedule itsef due to a lack of activity.
*/
enum FetchStatus {
Active,
Inactive
};
/** Individual thread status. */
enum ThreadStatus {
Running,
Idle,
Squashing,
Blocked,
Fetching,
TrapPending,
QuiescePending,
SwitchOut,
IcacheMissStall,
IcacheMissComplete
};
/** Fetching Policy, Add new policies here.*/
enum FetchPriority {
SingleThread,
RoundRobin,
Branch,
IQ,
LSQ
};
private:
/** Fetch status. */
FetchStatus _status;
/** Per-thread status. */
ThreadStatus fetchStatus[Impl::MaxThreads];
/** Fetch policy. */
FetchPriority fetchPolicy;
/** List that has the threads organized by priority. */
std::list<unsigned> priorityList;
public:
class CacheCompletionEvent : public Event
{
private:
MemReqPtr req;
/** Pointer to fetch. */
DefaultFetch *fetch;
/** Thread id. */
// unsigned threadId;
public:
/** Constructs a cache completion event, which tells fetch when the
* cache miss is complete.
*/
CacheCompletionEvent(MemReqPtr &_req, DefaultFetch *_fetch);
/** Processes cache completion event. */
virtual void process();
/** Returns the description of the cache completion event. */
virtual const char *description();
};
public:
/** DefaultFetch constructor. */
DefaultFetch(Params *params);
/** Returns the name of fetch. */
std::string name() const;
/** Registers statistics. */
void regStats();
/** Sets CPU pointer. */
void setCPU(FullCPU *cpu_ptr);
/** Sets the main backwards communication time buffer pointer. */
void setTimeBuffer(TimeBuffer<TimeStruct> *time_buffer);
/** Sets pointer to list of active threads. */
void setActiveThreads(std::list<unsigned> *at_ptr);
/** Sets pointer to time buffer used to communicate to the next stage. */
void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr);
/** Sets pointer to page table. */
// void setPageTable(PageTable *pt_ptr);
/** Initialize stage. */
void initStage();
/** Processes cache completion event. */
void processCacheCompletion(MemReqPtr &req);
void switchOut();
void doSwitchOut();
void takeOverFrom();
bool isSwitchedOut() { return switchedOut; }
void wakeFromQuiesce();
private:
/** Changes the status of this stage to active, and indicates this
* to the CPU.
*/
inline void switchToActive();
/** Changes the status of this stage to inactive, and indicates
* this to the CPU.
*/
inline void switchToInactive();
/**
* Looks up in the branch predictor to see if the next PC should be
* either next PC+=MachInst or a branch target.
* @param next_PC Next PC variable passed in by reference. It is
* expected to be set to the current PC; it will be updated with what
* the next PC will be.
* @return Whether or not a branch was predicted as taken.
*/
bool lookupAndUpdateNextPC(DynInstPtr &inst, Addr &next_PC);
/**
* Fetches the cache line that contains fetch_PC. Returns any
* fault that happened. Puts the data into the class variable
* cacheData.
* @param fetch_PC The PC address that is being fetched from.
* @param ret_fault The fault reference that will be set to the result of
* the icache access.
* @param tid Thread id.
* @return Any fault that occured.
*/
bool fetchCacheLine(Addr fetch_PC, Fault &ret_fault, unsigned tid);
/** Squashes a specific thread and resets the PC. */
inline void doSquash(const Addr &new_PC, unsigned tid);
/** Squashes a specific thread and resets the PC. Also tells the CPU to
* remove any instructions between fetch and decode that should be sqaushed.
*/
void squashFromDecode(const Addr &new_PC, const InstSeqNum &seq_num,
unsigned tid);
/** Checks if a thread is stalled. */
bool checkStall(unsigned tid) const;
/** Updates overall fetch stage status; to be called at the end of each
* cycle. */
FetchStatus updateFetchStatus();
public:
/** Squashes a specific thread and resets the PC. Also tells the CPU to
* remove any instructions that are not in the ROB. The source of this
* squash should be the commit stage.
*/
void squash(const Addr &new_PC, unsigned tid);
/** Ticks the fetch stage, processing all inputs signals and fetching
* as many instructions as possible.
*/
void tick();
/** Checks all input signals and updates the status as necessary.
* @return: Returns if the status has changed due to input signals.
*/
bool checkSignalsAndUpdate(unsigned tid);
/** Does the actual fetching of instructions and passing them on to the
* next stage.
* @param status_change fetch() sets this variable if there was a status
* change (ie switching to IcacheMissStall).
*/
void fetch(bool &status_change);
/** Align a PC to the start of an I-cache block. */
Addr icacheBlockAlignPC(Addr addr)
{
addr = TheISA::realPCToFetchPC(addr);
return (addr & ~(cacheBlkMask));
}
private:
/** Returns the appropriate thread to fetch, given the fetch policy. */
int getFetchingThread(FetchPriority &fetch_priority);
/** Returns the appropriate thread to fetch using a round robin policy. */
int roundRobin();
/** Returns the appropriate thread to fetch using the IQ count policy. */
int iqCount();
/** Returns the appropriate thread to fetch using the LSQ count policy. */
int lsqCount();
/** Returns the appropriate thread to fetch using the branch count policy. */
int branchCount();
private:
/** Pointer to the FullCPU. */
FullCPU *cpu;
/** Time buffer interface. */
TimeBuffer<TimeStruct> *timeBuffer;
/** Wire to get decode's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromDecode;
/** Wire to get rename's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromRename;
/** Wire to get iew's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromIEW;
/** Wire to get commit's information from backwards time buffer. */
typename TimeBuffer<TimeStruct>::wire fromCommit;
/** Internal fetch instruction queue. */
TimeBuffer<FetchStruct> *fetchQueue;
//Might be annoying how this name is different than the queue.
/** Wire used to write any information heading to decode. */
typename TimeBuffer<FetchStruct>::wire toDecode;
/** Icache interface. */
MemInterface *icacheInterface;
/** BPredUnit. */
BPredUnit branchPred;
Addr PC[Impl::MaxThreads];
Addr nextPC[Impl::MaxThreads];
/** Memory request used to access cache. */
MemReqPtr memReq[Impl::MaxThreads];
/** Variable that tracks if fetch has written to the time buffer this
* cycle. Used to tell CPU if there is activity this cycle.
*/
bool wroteToTimeBuffer;
/** Tracks how many instructions has been fetched this cycle. */
int numInst;
/** Source of possible stalls. */
struct Stalls {
bool decode;
bool rename;
bool iew;
bool commit;
};
/** Tracks which stages are telling fetch to stall. */
Stalls stalls[Impl::MaxThreads];
/** Decode to fetch delay, in ticks. */
unsigned decodeToFetchDelay;
/** Rename to fetch delay, in ticks. */
unsigned renameToFetchDelay;
/** IEW to fetch delay, in ticks. */
unsigned iewToFetchDelay;
/** Commit to fetch delay, in ticks. */
unsigned commitToFetchDelay;
/** The width of fetch in instructions. */
unsigned fetchWidth;
/** Cache block size. */
int cacheBlkSize;
/** Mask to get a cache block's address. */
Addr cacheBlkMask;
/** The cache line being fetched. */
uint8_t *cacheData[Impl::MaxThreads];
/** Size of instructions. */
int instSize;
/** Icache stall statistics. */
Counter lastIcacheStall[Impl::MaxThreads];
/** List of Active Threads */
std::list<unsigned> *activeThreads;
/** Number of threads. */
unsigned numThreads;
/** Number of threads that are actively fetching. */
unsigned numFetchingThreads;
/** Thread ID being fetched. */
int threadFetched;
bool interruptPending;
bool switchedOut;
#if !FULL_SYSTEM
/** Page table pointer. */
// PageTable *pTable;
#endif
// @todo: Consider making these vectors and tracking on a per thread basis.
/** Stat for total number of cycles stalled due to an icache miss. */
Stats::Scalar<> icacheStallCycles;
/** Stat for total number of fetched instructions. */
Stats::Scalar<> fetchedInsts;
Stats::Scalar<> fetchedBranches;
/** Stat for total number of predicted branches. */
Stats::Scalar<> predictedBranches;
/** Stat for total number of cycles spent fetching. */
Stats::Scalar<> fetchCycles;
/** Stat for total number of cycles spent squashing. */
Stats::Scalar<> fetchSquashCycles;
/** Stat for total number of cycles spent blocked due to other stages in
* the pipeline.
*/
Stats::Scalar<> fetchIdleCycles;
Stats::Scalar<> fetchBlockedCycles;
Stats::Scalar<> fetchMiscStallCycles;
/** Stat for total number of fetched cache lines. */
Stats::Scalar<> fetchedCacheLines;
Stats::Scalar<> fetchIcacheSquashes;
/** Distribution of number of instructions fetched each cycle. */
Stats::Distribution<> fetchNisnDist;
Stats::Formula idleRate;
Stats::Formula branchRate;
Stats::Formula fetchRate;
};
#endif //__CPU_O3_FETCH_HH__