gem5/src/cpu/o3/fu_pool.hh
Andreas Sandberg 1814a85a05 cpu: Rewrite O3 draining to avoid stopping in microcode
Previously, the O3 CPU could stop in the middle of a microcode
sequence. This patch makes sure that the pipeline stops when it has
committed a normal instruction or exited from a microcode
sequence. Additionally, it makes sure that the pipeline has no
instructions in flight when it is drained, which should make draining
more robust.

Draining is controlled in the commit stage, which checks if the next
PC after a committed instruction is in microcode. If this isn't the
case, it requests a squash of all instructions after that the
instruction that just committed and immediately signals a drain stall
to the fetch stage. The CPU then continues to execute until the
pipeline and all associated buffers are empty.
2013-01-07 13:05:46 -05:00

179 lines
6.3 KiB
C++

/*
* Copyright (c) 2012 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) 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.
*
* Authors: Kevin Lim
*/
#ifndef __CPU_O3_FU_POOL_HH__
#define __CPU_O3_FU_POOL_HH__
#include <bitset>
#include <list>
#include <string>
#include <vector>
#include "cpu/op_class.hh"
#include "params/FUPool.hh"
#include "sim/sim_object.hh"
class FUDesc;
class FuncUnit;
/**
* Pool of FU's, specific to the new CPU model. The old FU pool had lists of
* free units and busy units, and whenever a FU was needed it would iterate
* through the free units to find a FU that provided the capability. This pool
* has lists of units specific to each of the capabilities, and whenever a FU
* is needed, it iterates through that list to find a free unit. The previous
* FU pool would have to be ticked each cycle to update which units became
* free. This FU pool lets the IEW stage handle freeing units, which frees
* them as their scheduled execution events complete. This limits units in this
* model to either have identical issue and op latencies, or 1 cycle issue
* latencies.
*/
class FUPool : public SimObject
{
private:
/** Maximum op execution latencies, per op class. */
Cycles maxOpLatencies[Num_OpClasses];
/** Maximum issue latencies, per op class. */
Cycles maxIssueLatencies[Num_OpClasses];
/** Bitvector listing capabilities of this FU pool. */
std::bitset<Num_OpClasses> capabilityList;
/** Bitvector listing which FUs are busy. */
std::vector<bool> unitBusy;
/** List of units to be freed at the end of this cycle. */
std::vector<int> unitsToBeFreed;
/**
* Class that implements a circular queue to hold FU indices. The hope is
* that FUs that have been just used will be moved to the end of the queue
* by iterating through it, thus leaving free units at the head of the
* queue.
*/
class FUIdxQueue {
public:
/** Constructs a circular queue of FU indices. */
FUIdxQueue()
: idx(0), size(0)
{ }
/** Adds a FU to the queue. */
inline void addFU(int fu_idx);
/** Returns the index of the FU at the head of the queue, and changes
* the index to the next element.
*/
inline int getFU();
private:
/** Circular queue index. */
int idx;
/** Size of the queue. */
int size;
/** Queue of FU indices. */
std::vector<int> funcUnitsIdx;
};
/** Per op class queues of FUs that provide that capability. */
FUIdxQueue fuPerCapList[Num_OpClasses];
/** Number of FUs. */
int numFU;
/** Functional units. */
std::vector<FuncUnit *> funcUnits;
typedef std::vector<FuncUnit *>::iterator fuListIterator;
public:
typedef FUPoolParams Params;
/** Constructs a FU pool. */
FUPool(const Params *p);
~FUPool();
/** Annotates units that provide memory operations. Included only because
* old FU pool provided this function.
*/
void annotateMemoryUnits(Cycles hit_latency);
/**
* Gets a FU providing the requested capability. Will mark the unit as busy,
* but leaves the freeing of the unit up to the IEW stage.
* @param capability The capability requested.
* @return Returns -2 if the FU pool does not have the capability, -1 if
* there is no free FU, and the FU's index otherwise.
*/
int getUnit(OpClass capability);
/** Frees a FU at the end of this cycle. */
void freeUnitNextCycle(int fu_idx);
/** Frees all FUs on the list. */
void processFreeUnits();
/** Returns the total number of FUs. */
int size() { return numFU; }
/** Debugging function used to dump FU information. */
void dump();
/** Returns the operation execution latency of the given capability. */
Cycles getOpLatency(OpClass capability) {
return maxOpLatencies[capability];
}
/** Returns the issue latency of the given capability. */
Cycles getIssueLatency(OpClass capability) {
return maxIssueLatencies[capability];
}
/** Perform sanity checks after a drain. */
void drainSanityCheck() const;
/** Takes over from another CPU's thread. */
void takeOverFrom() {};
};
#endif // __CPU_O3_FU_POOL_HH__