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Part model
Ovni has a model to represent the hardware components as well as the software concepts like threads or processes. Each concept is considered to be a part. Here is an example diagram depicting the part hierarchy:
Notice how a loom can restrict the CPUs of the node to its child processes.
Software parts
These are not physical parts, but they abstract common concepts.
Thread
A thread in ovni is directly mapped to a POSIX
thread and they are identified by a
TID which must be unique in a node. Threads in ovni have a model with
an internal state that tries to tracks the
state of the real thread.
Process
A process is directly mapped to a UNIX
process and they are
identified by a PID number which must be unique in a node.
Loom
A loom has no direct mapping to a usual concept. It consists of a set of CPUs from the same node and a set of processes that can only run in those CPUs. Each CPUs must belong to one and only one loom. It is often used to group CPUs that belong to the same process when running workloads with multiple processes (like with MPI).
Each loom has a virtual CPU which collects running threads that are not exclusively assigned to a physical CPU, so we cannot determine on which CPU they are running.
Hardware parts
These parts have a physical object assigned.
CPU
A CPU is a hardware thread that can execute at most one thread at a time. Each CPU must have a physical ID that is unique in a node. In ovni there is also a virtual CPU, which simply is used to collect threads that are not tied to an specific physical CPU, so it cannot be easily determined where they are running.
Node
A node refers to a compute node, often a physical machine with memory and network which may contain one or more sockets, where each socket has one or more CPUs.
System
A system represents the complete set of hardware parts and software parts that are known to ovni in a given trace.