gem5/src/cpu/minor/buffers.hh
Andrew Bardsley 0e8a90f06b cpu: `Minor' in-order CPU model
This patch contains a new CPU model named `Minor'. Minor models a four
stage in-order execution pipeline (fetch lines, decompose into
macroops, decompose macroops into microops, execute).

The model was developed to support the ARM ISA but should be fixable
to support all the remaining gem5 ISAs. It currently also works for
Alpha, and regressions are included for ARM and Alpha (including Linux
boot).

Documentation for the model can be found in src/doc/inside-minor.doxygen and
its internal operations can be visualised using the Minorview tool
utils/minorview.py.

Minor was designed to be fairly simple and not to engage in a lot of
instruction annotation. As such, it currently has very few gathered
stats and may lack other gem5 features.

Minor is faster than the o3 model. Sample results:

     Benchmark     |   Stat host_seconds (s)
    ---------------+--------v--------v--------
     (on ARM, opt) | simple | o3     | minor
                   | timing | timing | timing
    ---------------+--------+--------+--------
    10.linux-boot  |   169  |  1883  |  1075
    10.mcf         |   117  |   967  |   491
    20.parser      |   668  |  6315  |  3146
    30.eon         |   542  |  3413  |  2414
    40.perlbmk     |  2339  | 20905  | 11532
    50.vortex      |   122  |  1094  |   588
    60.bzip2       |  2045  | 18061  |  9662
    70.twolf       |   207  |  2736  |  1036
2014-07-23 16:09:04 -05:00

653 lines
20 KiB
C++

/*
* Copyright (c) 2013-2014 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.
*
* 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: Andrew Bardsley
*/
/**
* @file
*
* Classes for buffer, queue and FIFO behaviour.
*/
#ifndef __CPU_MINOR_BUFFERS_HH__
#define __CPU_MINOR_BUFFERS_HH__
#include <iostream>
#include <queue>
#include <sstream>
#include "cpu/minor/trace.hh"
#include "cpu/activity.hh"
#include "cpu/timebuf.hh"
namespace Minor
{
/** Interface class for data with reporting/tracing facilities. This
* interface doesn't actually have to be used as other classes which need
* this interface uses templating rather than inheritance but it's provided
* here to document the interface needed by those classes. */
class ReportIF
{
public:
/** Print the data in a format suitable to be the value in "name=value"
* trace lines */
virtual void reportData(std::ostream &os) const = 0;
virtual ~ReportIF() { }
};
/** Interface class for data with 'bubble' values. This interface doesn't
* actually have to be used as other classes which need this interface uses
* templating rather than inheritance but it's provided here to document
* the interface needed by those classes. */
class BubbleIF
{
public:
virtual bool isBubble() const = 0;
};
/** ...ReportTraits are trait classes with the same functionality as
* ReportIF, but with elements explicitly passed into the report...
* functions. */
/** Allow a template using ReportTraits to call report... functions of
* ReportIF-bearing elements themselves */
template <typename ElemType> /* ElemType should implement ReportIF */
class ReportTraitsAdaptor
{
public:
static void
reportData(std::ostream &os, const ElemType &elem)
{ elem.reportData(os); }
};
/** A similar adaptor but for elements held by pointer
* ElemType should implement ReportIF */
template <typename PtrType>
class ReportTraitsPtrAdaptor
{
public:
static void
reportData(std::ostream &os, const PtrType &elem)
{ elem->reportData(os); }
};
/** ... BubbleTraits are trait classes to add BubbleIF interface
* functionality to templates which process elements which don't necessarily
* implement BubbleIF themselves */
/** Default behaviour, no bubbles */
template <typename ElemType>
class NoBubbleTraits
{
public:
static bool isBubble(const ElemType &) { return false; }
static ElemType bubble() { assert(false); }
};
/** Pass on call to the element */
template <typename ElemType>
class BubbleTraitsAdaptor
{
public:
static bool isBubble(const ElemType &elem)
{ return elem.isBubble(); }
static ElemType bubble() { return ElemType::bubble(); }
};
/** Pass on call to the element where the element is a pointer */
template <typename PtrType, typename ElemType>
class BubbleTraitsPtrAdaptor
{
public:
static bool isBubble(const PtrType &elem)
{ return elem->isBubble(); }
static PtrType bubble() { return ElemType::bubble(); }
};
/** TimeBuffer with MinorTrace and Named interfaces */
template <typename ElemType,
typename ReportTraits = ReportTraitsAdaptor<ElemType>,
typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
class MinorBuffer : public Named, public TimeBuffer<ElemType>
{
protected:
/** The range of elements that should appear in trace lines */
int reportLeft, reportRight;
/** Name to use for the data in a MinorTrace line */
std::string dataName;
public:
MinorBuffer(const std::string &name,
const std::string &data_name,
int num_past, int num_future,
int report_left = -1, int report_right = -1) :
Named(name), TimeBuffer<ElemType>(num_past, num_future),
reportLeft(report_left), reportRight(report_right),
dataName(data_name)
{ }
public:
/* Is this buffer full of only bubbles */
bool
empty() const
{
bool ret = true;
for (int i = -this->past; i <= this->future; i++) {
if (!BubbleTraits::isBubble((*this)[i]))
ret = false;
}
return ret;
}
/** Report buffer states from 'slot' 'from' to 'to'. For example 0,-1
* will produce two slices with current (just assigned) and last (one
* advance() old) slices with the current (0) one on the left.
* Reverse the numbers to change the order of slices */
void
minorTrace() const
{
std::ostringstream data;
int step = (reportLeft > reportRight ? -1 : 1);
int end = reportRight + step;
int i = reportLeft;
while (i != end) {
const ElemType &datum = (*this)[i];
ReportTraits::reportData(data, datum);
i += step;
if (i != end)
data << ',';
}
MINORTRACE("%s=%s\n", dataName, data.str());
}
};
/** Wraps a MinorBuffer with Input/Output interfaces to ensure that units
* within the model can only see the right end of buffers between them. */
template <typename Data>
class Latch
{
public:
typedef MinorBuffer<Data> Buffer;
protected:
/** Delays, in cycles, writing data into the latch and seeing it on the
* latched wires */
Cycles delay;
Buffer buffer;
public:
/** forward/backwardDelay specify the delay from input to output in each
* direction. These arguments *must* be >= 1 */
Latch(const std::string &name,
const std::string &data_name,
Cycles delay_ = Cycles(1),
bool report_backwards = false) :
delay(delay_),
buffer(name, data_name, delay_, 0, (report_backwards ? -delay_ : 0),
(report_backwards ? 0 : -delay_))
{ }
public:
/** Encapsulate wires on either input or output of the latch.
* forward/backward correspond to data direction relative to the
* pipeline. Latched and Immediate specify delay for backward data.
* Immediate data is available to earlier stages *during* the cycle it
* is written */
class Input
{
public:
typename Buffer::wire inputWire;
public:
Input(typename Buffer::wire input_wire) :
inputWire(input_wire)
{ }
};
class Output
{
public:
typename Buffer::wire outputWire;
public:
Output(typename Buffer::wire output_wire) :
outputWire(output_wire)
{ }
};
bool empty() const { return buffer.empty(); }
/** An interface to just the input of the buffer */
Input input() { return Input(buffer.getWire(0)); }
/** An interface to just the output of the buffer */
Output output() { return Output(buffer.getWire(-delay)); }
void minorTrace() const { buffer.minorTrace(); }
void evaluate() { buffer.advance(); }
};
/** A pipeline simulating class that will stall (not advance when advance()
* is called) if a non-bubble value lies at the far end of the pipeline.
* The user can clear the stall before calling advance to unstall the
* pipeline. */
template <typename ElemType,
typename ReportTraits,
typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
class SelfStallingPipeline : public MinorBuffer<ElemType, ReportTraits>
{
protected:
/** Wire at the input end of the pipeline (for convenience) */
typename TimeBuffer<ElemType>::wire pushWire;
/** Wire at the output end of the pipeline (for convenience) */
typename TimeBuffer<ElemType>::wire popWire;
public:
/** If true, advance will not advance the pipeline */
bool stalled;
/** The number of slots with non-bubbles in them */
unsigned int occupancy;
public:
SelfStallingPipeline(const std::string &name,
const std::string &data_name,
unsigned depth) :
MinorBuffer<ElemType, ReportTraits>
(name, data_name, depth, 0, -1, -depth),
pushWire(this->getWire(0)),
popWire(this->getWire(-depth)),
stalled(false),
occupancy(0)
{
assert(depth > 0);
/* Write explicit bubbles to get around the case where the default
* constructor for the element type isn't good enough */
for (unsigned i = 0; i <= depth; i++)
(*this)[-i] = BubbleTraits::bubble();
}
public:
/** Write an element to the back of the pipeline. This doesn't cause
* the pipeline to advance until advance is called. Pushing twice
* without advance-ing will just cause an overwrite of the last push's
* data. */
void push(ElemType &elem)
{
assert(!alreadyPushed());
*pushWire = elem;
if (!BubbleTraits::isBubble(elem))
occupancy++;
}
/** Peek at the end element of the pipe */
ElemType &front() { return *popWire; }
const ElemType &front() const { return *popWire; }
/** Have we already pushed onto this pipe without advancing */
bool alreadyPushed() { return !BubbleTraits::isBubble(*pushWire); }
/** There's data (not a bubble) at the end of the pipe */
bool isPopable() { return !BubbleTraits::isBubble(front()); }
/** Try to advance the pipeline. If we're stalled, don't advance. If
* we're not stalled, advance then check to see if we become stalled
* (a non-bubble at the end of the pipe) */
void
advance()
{
bool data_at_end = isPopable();
if (!stalled) {
TimeBuffer<ElemType>::advance();
/* If there was data at the end of the pipe that has now been
* advanced out of the pipe, we've lost data */
if (data_at_end)
occupancy--;
/* Is there data at the end of the pipe now? */
stalled = isPopable();
/* Insert a bubble into the empty input slot to make sure that
* element is correct in the case where the default constructor
* for ElemType doesn't produce a bubble */
ElemType bubble = BubbleTraits::bubble();
*pushWire = bubble;
}
}
};
/** Base class for space reservation requestable objects */
class Reservable
{
public:
/** Can a slot be reserved? */
virtual bool canReserve() const = 0;
/** Reserve a slot in whatever structure this is attached to */
virtual void reserve() = 0;
/** Free a reserved slot */
virtual void freeReservation() = 0;
};
/** Wrapper for a queue type to act as a pipeline stage input queue.
* Handles capacity management, bubble value suppression and provides
* reporting.
*
* In an ideal world, ElemType would be derived from ReportIF and BubbleIF,
* but here we use traits and allow the Adaptors ReportTraitsAdaptor and
* BubbleTraitsAdaptor to work on data which *does* directly implement
* those interfaces. */
template <typename ElemType,
typename ReportTraits = ReportTraitsAdaptor<ElemType>,
typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
class Queue : public Named, public Reservable
{
private:
std::deque<ElemType> queue;
/** Number of slots currently reserved for future (reservation
* respecting) pushes */
unsigned int numReservedSlots;
/** Need this here as queues usually don't have a limited capacity */
unsigned int capacity;
/** Name to use for the data in MinorTrace */
std::string dataName;
public:
Queue(const std::string &name, const std::string &data_name,
unsigned int capacity_) :
Named(name),
numReservedSlots(0),
capacity(capacity_),
dataName(data_name)
{ }
virtual ~Queue() { }
public:
/** Push an element into the buffer if it isn't a bubble. Bubbles are
* just discarded. It is assummed that any push into a queue with
* reserved space intends to take that space */
void
push(ElemType &data)
{
if (!BubbleTraits::isBubble(data)) {
freeReservation();
queue.push_back(data);
if (queue.size() > capacity) {
warn("%s: No space to push data into queue of capacity"
" %u, pushing anyway\n", name(), capacity);
}
}
}
/** Clear all allocated space. Be careful how this is used */
void clearReservedSpace() { numReservedSlots = 0; }
/** Clear a single reserved slot */
void freeReservation()
{
if (numReservedSlots != 0)
numReservedSlots--;
}
/** Reserve space in the queue for future pushes. Enquiries about space
* in the queue using unreservedRemainingSpace will only tell about
* space which is not full and not reserved. */
void
reserve()
{
/* Check reservable space */
if (unreservedRemainingSpace() == 0)
warn("%s: No space is reservable in queue", name());
numReservedSlots++;
}
bool canReserve() const { return unreservedRemainingSpace() != 0; }
/** Number of slots available in an empty buffer */
unsigned int totalSpace() const { return capacity; }
/** Number of slots already occupied in this buffer */
unsigned int occupiedSpace() const { return queue.size(); }
/** Number of slots which are reserved. */
unsigned int reservedSpace() const { return numReservedSlots; }
/** Number of slots yet to fill in this buffer. This doesn't include
* reservation. */
unsigned int
remainingSpace() const
{
int ret = capacity - queue.size();
return (ret < 0 ? 0 : ret);
}
/** Like remainingSpace but does not count reserved spaces */
unsigned int
unreservedRemainingSpace() const
{
int ret = capacity - (queue.size() + numReservedSlots);
return (ret < 0 ? 0 : ret);
}
/** Head value. Like std::queue::front */
ElemType &front() { return queue.front(); }
const ElemType &front() const { return queue.front(); }
/** Pop the head item. Like std::queue::pop */
void pop() { queue.pop_front(); }
/** Is the queue empty? */
bool empty() const { return queue.empty(); }
void
minorTrace() const
{
std::ostringstream data;
/* If we become over-full, totalSpace() can actually be smaller than
* occupiedSpace(). Handle this */
unsigned int num_total = (occupiedSpace() > totalSpace() ?
occupiedSpace() : totalSpace());
unsigned int num_reserved = reservedSpace();
unsigned int num_occupied = occupiedSpace();
int num_printed = 1;
/* Bodge to rotate queue to report elements */
while (num_printed <= num_occupied) {
ReportTraits::reportData(data, queue[num_printed - 1]);
num_printed++;
if (num_printed <= num_total)
data << ',';
}
int num_printed_reserved = 1;
/* Show reserved slots */
while (num_printed_reserved <= num_reserved &&
num_printed <= num_total)
{
data << 'R';
num_printed_reserved++;
num_printed++;
if (num_printed <= num_total)
data << ',';
}
/* And finally pad with empty slots (if there are any) */
while (num_printed <= num_total) {
num_printed++;
if (num_printed <= num_total)
data << ',';
}
MINORTRACE("%s=%s\n", dataName, data.str());
}
};
/** Like a Queue but with a restricted interface and a setTail function
* which, when the queue is empty, just takes a reference to the pushed
* item as the single element. Calling pushTail will push that element
* onto the queue.
*
* The purpose of this class is to allow the faster operation of queues of
* items which usually don't get deeper than one item and for which the copy
* associated with a push is expensive enough to want to avoid
*
* The intended use case is the input buffer for pipeline stages, hence the
* class name */
template <typename ElemType,
typename ReportTraits = ReportTraitsAdaptor<ElemType>,
typename BubbleTraits = BubbleTraitsAdaptor<ElemType> >
class InputBuffer : public Reservable
{
protected:
/** Underlying queue */
mutable Queue<ElemType, ReportTraits, BubbleTraits> queue;
/** Pointer to the single element (if not NULL) */
mutable ElemType *elementPtr;
public:
InputBuffer(const std::string &name, const std::string &data_name,
unsigned int capacity_) :
queue(name, data_name, capacity_),
elementPtr(NULL)
{ }
public:
/** Set the tail of the queue, this is like push but needs
* to be followed by pushTail for the new tail to make its
* way into the queue proper */
void
setTail(ElemType &new_element)
{
assert(!elementPtr);
if (!BubbleTraits::isBubble(new_element)) {
if (queue.empty())
elementPtr = &new_element;
else
queue.push(new_element);
}
}
/** No single element or queue entries */
bool empty() const { return !elementPtr && queue.empty(); }
/** Return the element, or the front of the queue */
const ElemType &front() const
{ return (elementPtr ? *elementPtr : queue.front()); }
ElemType &front()
{ return (elementPtr ? *elementPtr : queue.front()); }
/** Pop either the head, or if none, the head of the queue */
void
pop()
{
if (elementPtr) {
/* A popped element was expected to be pushed into queue
* and so take a reserved space */
elementPtr = NULL;
queue.freeReservation();
} else {
queue.pop();
}
}
/** Push the single element (if any) into the queue proper. If the
* element's reference points to a transient object, remember to
* always do this before the end of that object's life */
void
pushTail() const
{
if (elementPtr)
queue.push(*elementPtr);
elementPtr = NULL;
}
/** Report elements */
void
minorTrace() const
{
pushTail();
queue.minorTrace();
}
/** Reservable interface, passed on to queue */
bool canReserve() const { return queue.canReserve(); }
void reserve() { queue.reserve(); }
void freeReservation() { queue.freeReservation(); }
/** Like remainingSpace but does not count reserved spaces */
unsigned int
unreservedRemainingSpace()
{
pushTail();
return queue.unreservedRemainingSpace();
}
};
}
#endif /* __CPU_MINOR_BUFFERS_HH__ */