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Nanos6 model
The Nanos6 emulator generates four different Paraver views, which are explained in this document.
Task id
The task id view represents the id of the Nanos6 task instance that is currently executing on each thread/cpu. This id is a monotonically increasing identifier assigned on task creation. Lower ids correspond to tasks created at an earlier point than higher ids.
Task type
Every task in Nanos6 contains a task type, which roughly corresponds to the actual location in the code a task was declared. For example if a function fn() is declared as a Nanos6 task, and it is called multiple times in a program, every created task will have a different id, but the same type.
In the view, each type is shown with a label declared in the source with the label() attribute of the task. If no label was specified, one is automatically generated for each type.
Note that in this view, event value is a hash function of the type label, so two distinct types (tasks declared in different parts of the code) with the same label will share event value and will hence be indistinguishable.
MPI Rank
Represents the current MPI rank for the currently running task in a thread or cpu.
Subsystem view
The subsystem view attempts to provide a general overview of what the runtime is doing at any point in time. This view is more complex to understand than the others but is generally the most useful to understand what is happening and debug problems related with the runtime.
The view shows the state of the runtime for each thread (and for each CPU, the state of the running thread in that CPU).
The state is computed by the following method: the runtime code is completely divided into sections of code (machine instructions) S1, S2, ..., SN, which are instrumented (an event is emitted when entering and exiting each section), and one common section of code which is shared across the subsystems, U, of no interest. We also assume any other code not belonging to the runtime to be in the U section.
!!! remark
Every instruction of the runtime belongs to *exactly one section*.
To determine the state of a thread, we look into the stack to see what is the top-most instrumented section.
At any given point in time, a thread may be executing code with a stack that spawns multiple sections, for example S1, U, S2, S3 and U (the last is on top). The subsystem view selects the last subsystem section from the stack ignoring the common section U, and presents that section as the current state of the execution, in this case the S3.
Additionally, the runtime sections are grouped together in subsystems, which form a group of closely related functions. A complete set of states for each subsystem is listed below.
When there is no instrumented section in the thread stack, the state is set to No subsystem.
Task subsystem
The Task subsystem contains the code that controls the lifecycle of tasks. It contains the following sections:
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Running: Executing the body of the task (user defined code).
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Spawning function: Registering a new spawn function (programmatically created task)
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Creating: Creating a new task, through
nanos6_create_task -
Submitting: Submitting a recently created task, through
nanos6_submit_task
Scheduler subsystem
The Scheduler system groups the actions that relate to the queueing and dequeueing of ready tasks. It contains the following sections:
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Waiting for tasks: Actively waiting for tasks inside the scheduler subsystem, registered but not holding the scheduler lock
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Serving tasks: Inside the scheduler lock, serving tasks to other threads
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Adding ready tasks: Adding tasks to the scheduler queues, but outside of the scheduler lock.
Dependency subsystem
The Dependency system only contains the code that manages the registration of task dependencies. It contains the following sections:
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Registering: Registering a task's dependencies
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Unregistering: Releasing a task's dependencies because it has ended
Blocking subsystem
The Blocking subsystem deals with the code stops the thread execution. It contains the following sections:
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Taskwait: Task is blocked while inside a taskwait
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Blocking current task: Task is blocked through the Nanos6 blocking API
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Unblocking remote task: Unblocking a different task using the Nanos6 blocking API
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Wait For: Blocking a deadline task, which will be re-enqueued when a certain amount of time has passed