58 lines
2.3 KiB
Markdown
58 lines
2.3 KiB
Markdown
# Emulation overview
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The emulator `ovniemu` reads the events stored during runtime and
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reconstructs the execution, restoring the state of each thread and CPU
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as time evolves. During the emulation process, a detailed trace is
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generated with the state of the execution in the Paraver PRV format.
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The emulator has an execution model to represent the real execution that
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happened on the hardware. It consists of CPUs which can execute multiple threads
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at the same time.
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The emulator uses several models to identify how the resources are being
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used. The following diagram depicts the resource, process and task
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model.
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[](fig/model.svg)
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The resource model directly maps to the available hardware on the
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machine. It consists of a cluster which contains nodes, where each node
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contains a set of CPUs that can execute instructions.
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The process model tracks the state of processes and threads. Processes
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that use the same CPUs in a single node are grouped into looms.
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The task model includes the information of MPI and tasks of the
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programming model (OmpSs-2).
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## Design considerations
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The emulator tries to perform every posible check to detect if there is
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any inconsistency in the received events from the runtime trace. When a
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problem is found, the emulation is aborted, forcing the user to report
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the problem. No effort is made to let the emulator recover from an
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inconsistency.
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The emulator critical path is kept as simple as possible, so the
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processing of events can keep the disk writing as the bottleneck.
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The lint mode enables more tests which are disabled from the default
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mode to prevent costly operations running in the emulator by default.
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The lint tests are enabled when running the ovni testsuite.
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## Emulation models
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Each component is implemented in an emulation model, which consists of
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the following elements:
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- A single byte model identification (for example `O`).
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- A set of runtime events with that model identification (see the [list
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of events](events)).
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- Rules that determine which sequences of events are valid.
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- The emulation hooks that process each event and modify the state of
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the emulator.
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- A set of channels that output the states from the emulator.
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- A set of Paraver views that present the information in a timeline.
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All the models are independent and can be instrumented at the same time.
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