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