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| Getting Started |
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| <a class="subitem " href="/building">Building gem5</a> |
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| <a class="subitem " href="/simple_config">Creating a simple configuration script</a> |
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| Modifying/Extending |
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| <a class="subitem " href="/environment">Setting up your development environment</a> |
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| <a class="subitem " href="/helloobject">Creating a very simple SimObject</a> |
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| Modeling Cache Coherence with Ruby |
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| <a class="subitem active" href="/MSIintro">Introduction to Ruby</a> |
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| <a class="subitem " href="/cache-intro">MSI example cache protocol</a> |
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| <a class="subitem " href="/cache-declarations">Declaring a state machine</a> |
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| <a class="subitem " href="/cache-in-ports">In port code blocks</a> |
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| <a class="subitem " href="/cache-actions">Action code blocks</a> |
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| <a class="subitem " href="/directory">MSI Directory implementation</a> |
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| <a class="subitem " href="/MSIbuilding">Compiling a SLICC protocol</a> |
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| <dl> |
| <dt>authors</dt> |
| <dd>Jason Lowe-Power</dd> |
| </dl> |
| |
| <h1 id="introduction-to-ruby">Introduction to Ruby</h1> |
| |
| <p>Ruby comes from the <a href="http://research.cs.wisc.edu/gems/">multifacet GEMS |
| project</a>. Ruby provides a detailed |
| cache memory and cache coherence models as well as a detailed network |
| model (Garnet).</p> |
| |
| <p>Ruby is flexible. It can model many different kinds of coherence |
| implementations, including broadcast, directory, token, region-based |
| coherence, and is simple to extend to new coherence models.</p> |
| |
| <p>Ruby is a mostly drop-in replacement for the classic memory system. |
| There are interfaces between the classic gem5 MemObjects and Ruby, but |
| for the most part, the classic caches and Ruby are not compatible.</p> |
| |
| <p>In this part of the book, we will first go through creating an example |
| protocol from the protocol description to debugging and running the |
| protocol.</p> |
| |
| <p>Before diving into a protocol, we will first talk about some of the |
| architecture of Ruby. The most important structure in Ruby is the |
| controller, or state machine. Controllers are implemented by writing a |
| SLICC state machine file.</p> |
| |
| <p>SLICC is a domain-specific language (Specification Language including |
| Cache Coherence) for specifying coherence protocols. SLICC files end in |
| “.sm” because they are <em>state machine</em> files. Each file describes |
| states, transitions from a begin to an end state on some event, and |
| actions to take during the transition.</p> |
| |
| <p>Each coherence protocol is made up of multiple SLICC state machine |
| files. These files are compiled with the SLICC compiler which is written |
| in Python and part of the gem5 source. The SLICC compiler takes the |
| state machine files and output a set of C++ files that are compiled with |
| all of gem5’s other files. These files include the SimObject declaration |
| file as well as implementation files for SimObjects and other C++ |
| objects.</p> |
| |
| <p>Currently, gem5 supports compiling only a single coherence protocol at a |
| time. For instance, you can compile MI_example into gem5 (the default, |
| poor performance, protocol), or you can use MESI_Two_Level. But, to |
| use MESI_Two_Level, you have to recompile gem5 so the SLICC compiler |
| can generate the correct files for the protocol. We discuss this further |
| in the compilation section <MSI-building-section></p> |
| |
| <p>Now, let’s dive into implementing our first coherence protocol!</p> |
| |
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