73 lines
2.6 KiB
Markdown
73 lines
2.6 KiB
Markdown
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# Trace model
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An event model is composed by a group of runtime events
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## Trace
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The information generated by a program or later processed by other ovni tools is
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known as a trace. A runtime trace stores the information as-is in disk from a
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program execution. While a emulation trace is generated from the runtime trace
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for visualization with Paraver.
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All the information is always stored inside the same directory, by default
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`ovni/`, which is known as the trace directory.
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## Event
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An event is a point in time that has some information associated. Events written
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at runtime by libovni have at MCV, a clock and a optional payload. The list of
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all events recognized by the emulator can be found [here](../emulation/events.md).
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## State
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A state is a discrete value that can change over time based on the events the
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emulator receives. Usually a single event causes a single state change, which is
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then written to the Paraver traces. An example is the thread state, which can
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change over time based on the events `OH*` that indicate a state transition
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of the current thread.
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## MCV
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The MCV acronym is short of Model-Class-Value, which is a three character (byte)
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identification for events.
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## Clock
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A clock is a 64 bit counter, which counts the number of nanoseconds from an
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arbitrary point in time in the past. Each event has the value of the clock
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stored inside, to indicate when that event happened. In a given trace there can
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be multiple clocks which don't refer to the same point in the past and must be
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corrected so they all produce an ordered sequence of events. The ovnisync
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program performs this correction by measuring the difference across clocks of
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different nodes.
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## Event model
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An event model is composed of several components:
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- A set of [events](#event) all with the same model identifier in the
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[MCV](#mcv)
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- The emulator code that processes those events.
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- A human readable name, like `ovni` or `nanos6`.
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## Payload
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Events may have associated additional information which is stored in the stream.
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## Binary stream
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A binary stream is a file named `stream.obs` (.obs stands for Ovni Binary
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Stream) composed of a header and a concatenated array of events without padding.
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Notice that each event may have different length.
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## Stream metadata
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The stream metadata is a JSON file named `stream.json` which holds information
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about the stream.
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## Stream
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A stream is a directory which contains a binary stream and the associated stream
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metadata file. Each stream is associated with a given part of a system. As of
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now, libovni can only generate streams associated to [threads](part-model.md#thread).
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