gem5/src/mem/cache/cache_blk.hh

/*
 * Copyright (c) 2003-2005 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: Erik Hallnor
 */

/** @file
 * Definitions of a simple cache block class.
 */

#ifndef __CACHE_BLK_HH__
#define __CACHE_BLK_HH__

#include <list>

#include "sim/root.hh"		// for Tick
#include "arch/isa_traits.hh"	// for Addr
#include "mem/request.hh"

/**
 * Cache block status bit assignments
 */
enum CacheBlkStatusBits {
    /** valid, readable */
    BlkValid =		0x01,
    /** write permission */
    BlkWritable =	0x02,
    /** dirty (modified) */
    BlkDirty =		0x04,
    /** compressed */
    BlkCompressed =	0x08,
    /** block was referenced */
    BlkReferenced =	0x10,
    /** block was a hardware prefetch yet unaccessed*/
    BlkHWPrefetched =	0x20
};

/**
 * A Basic Cache block.
 * Contains the tag, status, and a pointer to data.
 */
class CacheBlk
{
  public:
    /** The address space ID of this block. */
    int asid;
    /** Data block tag value. */
    Addr tag;
    /**
     * Contains a copy of the data in this block for easy access. This is used
     * for efficient execution when the data could be actually stored in
     * another format (COW, compressed, sub-blocked, etc). In all cases the
     * data stored here should be kept consistant with the actual data
     * referenced by this block.
     */
    uint8_t *data;
    /** the number of bytes stored in this block. */
    int size;

    /** block state: OR of CacheBlkStatusBit */
    typedef unsigned State;

    /** The current status of this block. @sa CacheBlockStatusBits */
    State status;

    /** Which curTick will this block be accessable */
    Tick whenReady;

    /**
     * The set this block belongs to.
     * @todo Move this into subclasses when we fix CacheTags to use them.
     */
    int set;

    /** Number of references to this block since it was brought in. */
    int refCount;

  protected:
    /**
     * Represents that the indicated thread context has a "lock" on
     * the block, in the LL/SC sense.
     */
    class Lock {
      public:
        int cpuNum;	// locking CPU
        int threadNum;	// locking thread ID within CPU

        // check for matching execution context
        bool matchesContext(Request *req)
        {
            return (cpuNum == req->getCpuNum() &&
                    threadNum == req->getThreadNum());
        }

        Lock(Request *req)
            : cpuNum(req->getCpuNum()), threadNum(req->getThreadNum())
        {
        }
    };

    /** List of thread contexts that have performed a load-locked (LL)
     * on the block since the last store. */
    std::list<Lock> lockList;

  public:

    CacheBlk()
        : asid(-1), tag(0), data(0) ,size(0), status(0), whenReady(0),
          set(-1), refCount(0)
    {}

    /**
     * Copy the state of the given block into this one.
     * @param rhs The block to copy.
     * @return a const reference to this block.
     */
    const CacheBlk& operator=(const CacheBlk& rhs)
    {
        asid = rhs.asid;
        tag = rhs.tag;
        data = rhs.data;
        size = rhs.size;
        status = rhs.status;
        whenReady = rhs.whenReady;
        set = rhs.set;
        refCount = rhs.refCount;
        return *this;
    }

    /**
     * Checks the write permissions of this block.
     * @return True if the block is writable.
     */
    bool isWritable() const
    {
        const int needed_bits = BlkWritable | BlkValid;
        return (status & needed_bits) == needed_bits;
    }

    /**
     * Checks that a block is valid (readable).
     * @return True if the block is valid.
     */
    bool isValid() const
    {
        return (status & BlkValid) != 0;
    }

    /**
     * Check to see if a block has been written.
     * @return True if the block is dirty.
     */
    bool isModified() const
    {
        return (status & BlkDirty) != 0;
    }

    /**
     * Check to see if this block contains compressed data.
     * @return True iF the block's data is compressed.
     */
    bool isCompressed() const
    {
        return (status & BlkCompressed) != 0;
    }

    /**
     * Check if this block has been referenced.
     * @return True if the block has been referenced.
     */
    bool isReferenced() const
    {
        return (status & BlkReferenced) != 0;
    }

    /**
     * Check if this block was the result of a hardware prefetch, yet to
     * be touched.
     * @return True if the block was a hardware prefetch, unaccesed.
     */
    bool isPrefetch() const
    {
        return (status & BlkHWPrefetched) != 0;
    }

    /**
     * Track the fact that a local locked was issued to the block.  If
     * multiple LLs get issued from the same context we could have
     * redundant records on the list, but that's OK, as they'll all
     * get blown away at the next store.
     */
    void trackLoadLocked(Request *req)
    {
        assert(req->isLocked());
        lockList.push_front(Lock(req));
    }

    /**
     * Clear the list of valid load locks.  Should be called whenever
     * block is written to or invalidated.
     */
    void clearLoadLocks() { lockList.clear(); }

    /**
     * Handle interaction of load-locked operations and stores.
     * @return True if write should proceed, false otherwise.  Returns
     * false only in the case of a failed store conditional.
     */
    bool checkWrite(Request *req)
    {
        if (req->isLocked()) {
            // it's a store conditional... have to check for matching
            // load locked.
            bool success = false;

            for (std::list<Lock>::iterator i = lockList.begin();
                 i != lockList.end(); ++i)
            {
                if (i->matchesContext(req)) {
                    // it's a store conditional, and as far as the memory
                    // system can tell, the requesting context's lock is
                    // still valid.
                    success = true;
                    break;
                }
            }

            req->setScResult(success ? 1 : 0);
            clearLoadLocks();
            return success;
        } else {
            // for *all* stores (conditional or otherwise) we have to
            // clear the list of load-locks as they're all invalid now.
            clearLoadLocks();
            return true;
        }
    }
};

#endif //__CACHE_BLK_HH__