| /** |
| * Copyright (c) 2018 Inria |
| * 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. |
| */ |
| |
| /** @file |
| * Definition of a simple superblock class. Each superblock consists of a |
| * number of compressed cache blocks limited by the maximum compression |
| * factor that may or may not be present in the cache. |
| */ |
| |
| #ifndef __MEM_CACHE_TAGS_SUPER_BLK_HH__ |
| #define __MEM_CACHE_TAGS_SUPER_BLK_HH__ |
| |
| #include "mem/cache/tags/sector_blk.hh" |
| |
| namespace gem5 |
| { |
| |
| class SuperBlk; |
| |
| /** |
| * A superblock is composed of sub-blocks, and each sub-block has information |
| * regarding its superblock and a pointer to its superblock tag. A superblock |
| * can be seen as a variation of a sector block, and therefore we use a sector |
| * nomenclature. |
| */ |
| class CompressionBlk : public SectorSubBlk |
| { |
| private: |
| /** |
| * Set size, in bits, of this compressed block's data. |
| */ |
| std::size_t _size; |
| |
| /** |
| * Number of cycles needed to decompress this block. We store it to avoid |
| * doing decompressions. |
| */ |
| Cycles _decompressionLatency; |
| |
| /** Compression bit. */ |
| bool _compressed; |
| |
| public: |
| /** |
| * When an overwrite happens, the data size may change an not fit in its |
| * current container any longer. This enum declared which kind of size |
| * change happened in this situation. |
| */ |
| enum OverwriteType : int |
| { |
| /** New data contents are considered smaller than previous contents. */ |
| DATA_CONTRACTION = -1, |
| /** New and old contents are considered of similar sizes. */ |
| UNCHANGED = 0, |
| /** New data contents are considered larger than previous contents. */ |
| DATA_EXPANSION = 1, |
| }; |
| |
| CompressionBlk(); |
| CompressionBlk(const CompressionBlk&) = delete; |
| CompressionBlk& operator=(const CompressionBlk&) = delete; |
| CompressionBlk(CompressionBlk&&) = delete; |
| /** |
| * Move assignment operator. |
| * This should only be used to move an existing valid entry into an |
| * invalid one, not to create a new entry. In the end the valid entry |
| * will become invalid, and the invalid, valid. All location related |
| * variables will remain the same. |
| */ |
| CompressionBlk& operator=(CompressionBlk&& other); |
| CacheBlk& operator=(CacheBlk&& other) override; |
| ~CompressionBlk() = default; |
| |
| /** |
| * Check if this block holds compressed data. |
| * |
| * @return True if the block holds compressed data. |
| */ |
| bool isCompressed() const; |
| |
| /** |
| * Set compression bit. |
| */ |
| void setCompressed(); |
| |
| /** |
| * Clear compression bit. |
| */ |
| void setUncompressed(); |
| |
| /* |
| * Get size, in bits, of this compressed block's data. |
| * |
| * @return The compressed size. |
| */ |
| std::size_t getSizeBits() const; |
| |
| /** |
| * Set size, in bits, of this compressed block's data. |
| * |
| * @param The compressed size. |
| */ |
| void setSizeBits(const std::size_t size); |
| |
| /** |
| * Get number of cycles needed to decompress this block. |
| * |
| * @return Decompression latency. |
| */ |
| Cycles getDecompressionLatency() const; |
| |
| /** |
| * Set number of cycles needed to decompress this block. |
| * |
| * @param Decompression latency. |
| */ |
| void setDecompressionLatency(const Cycles lat); |
| |
| void invalidate() override; |
| |
| /** |
| * Determines if changing the size of the block will cause a data |
| * expansion (new size is bigger) or contraction (new size is smaller). |
| * Sizes are not necessarily compared at at bit granularities (e.g., 20 |
| * bits is considered equal to 23 bits when blocks use 32-bit spaces as |
| * minimum allocation units). |
| * |
| * @param size The new compressed size. |
| * @return Type of size change. @sa OverwriteType. |
| */ |
| OverwriteType checkExpansionContraction(const std::size_t size) const; |
| |
| /** |
| * Pretty-print sector offset and other CacheBlk information. |
| * |
| * @return string with basic state information |
| */ |
| std::string print() const override; |
| }; |
| |
| /** |
| * A basic compression superblock. |
| * Contains the tag and a list of blocks associated to this superblock. |
| */ |
| class SuperBlk : public SectorBlk |
| { |
| protected: |
| /** Block size, in bytes. */ |
| std::size_t blkSize; |
| |
| /** |
| * Superblock's compression factor. It is aligned to be a power of two, |
| * limited by the maximum compression ratio, and calculated as: |
| * compressionFactor = uncompressedSize/compressedSize |
| */ |
| uint8_t compressionFactor; |
| |
| public: |
| SuperBlk(); |
| SuperBlk(const SuperBlk&) = delete; |
| SuperBlk& operator=(const SuperBlk&) = delete; |
| ~SuperBlk() {}; |
| |
| /** |
| * Returns whether the superblock contains compressed blocks or not. By |
| * default, if not blocks are valid, the superblock is compressible. |
| * |
| * @param ignored_blk If provided don't consider the given block. |
| * @return The compressibility state of the superblock. |
| */ |
| bool isCompressed(const CompressionBlk* ignored_blk = nullptr) const; |
| |
| /** |
| * Checks whether a superblock can co-allocate given compressed data block. |
| * |
| * @param compressed_size Size, in bits, of new block to allocate. |
| * @return True if block can be co-allocated in superblock. |
| */ |
| bool canCoAllocate(const std::size_t compressed_size) const; |
| |
| /** |
| * Set block size. Should be called only once, when initializing blocks. |
| * |
| * @param blk_size The uncompressed block size. |
| */ |
| void setBlkSize(const std::size_t blk_size); |
| |
| /** |
| * Calculate the compression factor (cf) given a compressed size and the |
| * maximum compression ratio. Therefore cf is: |
| * 1 if comp_size > blk_size/2, |
| * 2 if comp_size > blk_size/4, |
| * 4 if comp_size > blk_size/8, |
| * 8 if comp_size > blk_size/16, |
| * and so on. |
| * |
| * @param size The compressed size. |
| * @return Compression factor corresponding to the size. |
| */ |
| uint8_t calculateCompressionFactor(const std::size_t size) const; |
| |
| /** |
| * Get the compression factor of this superblock. |
| * |
| * @return The compression factor. |
| */ |
| uint8_t getCompressionFactor() const; |
| |
| /** |
| * Set the compression factor of this superblock. |
| * |
| * @param compression_factor The new compression factor. |
| */ |
| void setCompressionFactor(const uint8_t compression_factor); |
| |
| void invalidate() override; |
| |
| std::string print() const override; |
| }; |
| |
| } // namespace gem5 |
| |
| #endif //__MEM_CACHE_TAGS_SUPER_BLK_HH__ |