Explain some concepts in the documentation
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# Overview
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The objective of the ovni project is to provide insight into what
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happened at execution of a program.
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The key pieces of software involved are instrumented so they emit events
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during the execution which allow the reconstruction of the execution
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later on.
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During the execution phase, the information gathered in the events is
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kept very short and simple, so the overhead is kept at minimum to avoid
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disturbing the execution process. Here is an example of a single event
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emitted during the execution phase, informing the current thread to
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finish the execution:
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00 4f 48 65 52 c0 27 b4 d3 ec 01 00
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During the emulation phase, the events are read and processed in the
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emulator, reconstructing the execution. State transitions are recorded
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in a Paraver trace. Here is an example of the same thread ceasing the
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execution:
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2:0:1:1:1:50105669:1:0
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Finally, loading the trace in the Paraver program, we can generate a
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timeline visualization of the state change. Here is the example for the
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same state transition of the thread stopping the execution:
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62
doc/user/concepts/part-model.md
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doc/user/concepts/part-model.md
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# Part model
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Ovni has a model to represent the hardware components as well as the software
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concepts like threads or processes. Each concept is considered to be a *part*.
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Here is an example diagram depicting the part hierarchy:
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Notice how a loom can restrict the CPUs of the node to its child processes.
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## Software parts
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These are not physical parts, but they abstract common concepts.
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### Thread
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A thread in ovni is directly mapped to a [POSIX
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thread](https://en.wikipedia.org/wiki/Pthreads) and they are identified by a
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`TID` which must be unique in a [node](#node). Threads in ovni have [a model with
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an internal state](../emulation/ovni.md/#thread_model) that tries to tracks the
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state of the real thread.
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### Process
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A process is directly mapped to a UNIX
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[process](https://en.wikipedia.org/wiki/Process_(computing)) and they are
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identified by a `PID` number which must be unique in a [node](#node).
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### Loom
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A loom has no direct mapping to a usual concept. It consists of a set of
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[CPUs](#cpu) from the same node and a set of processes that can *only run in
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those CPUs*. Each CPUs must belong to one and only one loom. It is often used
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to group CPUs that belong to the same process when running workloads with
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multiple processes (like with MPI).
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Each loom has a virtual CPU which collects running threads that are not
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exclusively assigned to a physical CPU, so we cannot determine on which CPU they
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are running.
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## Hardware parts
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These parts have a physical object assigned.
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### CPU
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A CPU is a hardware thread that can execute at most one thread at a time. Each
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CPU must have a physical ID that is unique in a node. In ovni there is also a
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virtual CPU, which simply is used to collect threads that are not tied to an
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specific physical CPU, so it cannot be easily determined where they are running.
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### Node
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A *node* refers to a compute node, often a physical machine with memory and
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network which may contain one or more
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[sockets](https://en.wikipedia.org/wiki/CPU_socket), where each socket has one
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or more CPUs.
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### System
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A system represents the complete set of hardware parts and software parts that
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are known to ovni in a given trace.
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72
doc/user/concepts/trace-model.md
Normal file
72
doc/user/concepts/trace-model.md
Normal file
@ -0,0 +1,72 @@
|
||||
# Trace model
|
||||
|
||||
An event model is composed by a group of runtime events
|
||||
|
||||
## Trace
|
||||
|
||||
The information generated by a program or later processed by other ovni tools is
|
||||
known as a trace. A runtime trace stores the information as-is in disk from a
|
||||
program execution. While a emulation trace is generated from the runtime trace
|
||||
for visualization with Paraver.
|
||||
|
||||
All the information is always stored inside the same directory, by default
|
||||
`ovni/`, which is known as the trace directory.
|
||||
|
||||
## Event
|
||||
|
||||
An event is a point in time that has some information associated. Events written
|
||||
at runtime by libovni have at MCV, a clock and a optional payload. The list of
|
||||
all events recognized by the emulator can be found [here](../emulation/events.md).
|
||||
|
||||
## State
|
||||
|
||||
A state is a discrete value that can change over time based on the events the
|
||||
emulator receives. Usually a single event causes a single state change, which is
|
||||
then written to the Paraver traces. An example is the thread state, which can
|
||||
change over time based on the events `OH*` that indicate a state transition
|
||||
of the current thread.
|
||||
|
||||
## MCV
|
||||
|
||||
The MCV acronym is short of Model-Class-Value, which is a three character (byte)
|
||||
identification for events.
|
||||
|
||||
## Clock
|
||||
|
||||
A clock is a 64 bit counter, which counts the number of nanoseconds from an
|
||||
arbitrary point in time in the past. Each event has the value of the clock
|
||||
stored inside, to indicate when that event happened. In a given trace there can
|
||||
be multiple clocks which don't refer to the same point in the past and must be
|
||||
corrected so they all produce an ordered sequence of events. The ovnisync
|
||||
program performs this correction by measuring the difference across clocks of
|
||||
different nodes.
|
||||
|
||||
## Event model
|
||||
|
||||
An event model is composed of several components:
|
||||
|
||||
- A set of [events](#event) all with the same model identifier in the
|
||||
[MCV](#mcv)
|
||||
- The emulator code that processes those events.
|
||||
- A human readable name, like `ovni` or `nanos6`.
|
||||
|
||||
## Payload
|
||||
|
||||
Events may have associated additional information which is stored in the stream.
|
||||
|
||||
## Binary stream
|
||||
|
||||
A binary stream is a file named `stream.obs` (.obs stands for Ovni Binary
|
||||
Stream) composed of a header and a concatenated array of events without padding.
|
||||
Notice that each event may have different length.
|
||||
|
||||
## Stream metadata
|
||||
|
||||
The stream metadata is a JSON file named `stream.json` which holds information
|
||||
about the stream.
|
||||
|
||||
## Stream
|
||||
|
||||
A stream is a directory which contains a binary stream and the associated stream
|
||||
metadata file. Each stream is associated with a given part of a system. As of
|
||||
now, libovni can only generate streams associated to [threads](part-model.md#thread).
|
||||
111
doc/user/runtime/index.md
Normal file
111
doc/user/runtime/index.md
Normal file
@ -0,0 +1,111 @@
|
||||
# Introduction
|
||||
|
||||
To use *libovni* to instrument a program, follow the next instructions
|
||||
carefully, or you may end up with an incomplete trace that is rejected at
|
||||
emulation.
|
||||
|
||||
You can also generate a valid trace from your own software or hardware
|
||||
directly, but be sure to follow the [trace specification](trace_spec.md).
|
||||
|
||||
## Initialization
|
||||
|
||||
To initialize libovni follow these steps in all threads:
|
||||
|
||||
1. **Check the version**. Call `ovni_version_check()` once before calling any
|
||||
ovni function. It can be called multiple times from any thread, but only one
|
||||
is required.
|
||||
|
||||
2. **Init the process**. Call `ovni_proc_init()` to initialize the process when
|
||||
a new process begins the execution. It can only be called **once per
|
||||
process** and it must be called before the thread is initialized.
|
||||
|
||||
3. **Init the thread**. Call `ovni_thread_init()` when a new thread begins the
|
||||
execution (including the main process thread after the process is
|
||||
initialized). Multiple attempts to initialize the thread are ignored with a
|
||||
warning.
|
||||
|
||||
The `ovni_proc_init()` arguments are as follows:
|
||||
|
||||
```c
|
||||
void ovni_proc_init(int app, const char *loom, int pid);
|
||||
```
|
||||
|
||||
The `app` defines the "appid" of the program, which must be a number >0. This is
|
||||
useful to run multiple processes some of which run the same "app", so you can
|
||||
tell which one is which. The `loom` defines the
|
||||
[loom](../concepts/part-model.md#loom) name and assignes the process to that
|
||||
loom. It must be compose of the host name, a dot and a suffix. The PID is the
|
||||
one obtained by `getpid(2)`.
|
||||
|
||||
The `ovni_thread_init()` function only accepts one argument, the TID as returned
|
||||
by `gettid(2)`.
|
||||
|
||||
## Setup metadata
|
||||
|
||||
Once the process and thread are initialized, you can begin adding metadata to
|
||||
the thread stream.
|
||||
|
||||
1. **Require models**. Call `ovni_thread_require()` with the required model
|
||||
version before emitting events for a given model. Only required once from a
|
||||
thread in a given trace.
|
||||
|
||||
2. **Emit loom CPUs**. Call `ovni_add_cpu()` to register each CPU in the loom. It can
|
||||
be done from a single thread or multiple threads, in the latter the list of
|
||||
CPUs is merged.
|
||||
|
||||
3. **Set the rank**. If you use MPI, call `ovni_proc_set_rank()` to register the
|
||||
rank and number of ranks of the current execution. Only once per process.
|
||||
|
||||
## Start the execution
|
||||
|
||||
The current thread must switch to the "Running" state before any event can be
|
||||
processed by the emulator. Do so by emitting a `OHx` event in the stream with
|
||||
the appropriate payload:
|
||||
|
||||
```c
|
||||
static void thread_execute(int32_t cpu, int32_t ctid, uint64_t tag)
|
||||
{
|
||||
struct ovni_ev ev = {0};
|
||||
ovni_ev_set_clock(&ev, ovni_clock_now());
|
||||
ovni_ev_set_mcv(&ev, "OHx");
|
||||
ovni_payload_add(&ev, (uint8_t *) &cpu, sizeof(cpu));
|
||||
ovni_payload_add(&ev, (uint8_t *) &ctid, sizeof(ctid));
|
||||
ovni_payload_add(&ev, (uint8_t *) &tag, sizeof(tag));
|
||||
ovni_ev_emit(&ev);
|
||||
}
|
||||
```
|
||||
|
||||
The `cpu` is the logical index (not the physical ID) of the loom CPU at which
|
||||
this thread will begin the execution. Use -1 if it is not known. The `ctid` and
|
||||
`tag` allow you to track the exact point at which a given thread was created and
|
||||
by which thread but they are not relevant for the first thread, so they can be
|
||||
set to -1.
|
||||
|
||||
## Emit events
|
||||
|
||||
After this point you can emit any other event from this thread. Use the
|
||||
`ovni_ev_*` set of functions to create and emit events. Notice that all events
|
||||
are refer to the current thread that emits them.
|
||||
|
||||
If you need to store metadata information, use the `ovni_attr_*` set of
|
||||
functions. The metadata is stored in disk by `ovni_attr_fluch()` and when the
|
||||
thread is freed by `ovni_thread_free()`.
|
||||
|
||||
Attempting to emit events or writing metadata without having a thread
|
||||
initialized will cause your program to abort.
|
||||
|
||||
## Finishing the execution
|
||||
|
||||
To finalize the execution **every thread** must perform the following steps,
|
||||
otherwise the trace **will be rejected**.
|
||||
|
||||
1. **End the current thread**. Emit a [`OHe` event](../emulation/events.md#OHe) to inform the current thread ends.
|
||||
2. **Flush the buffer**. Call `ovni_flush()` to be sure all events are written
|
||||
to disk.
|
||||
3. **Free the thread**. Call `ovni_thread_free()` to complete the stream and
|
||||
free the memory used by the buffer.
|
||||
4. **Finish the process**. If this is the last thread, call `ovni_proc_fini()`
|
||||
to set the process state to finished.
|
||||
|
||||
If a thread fails to perform these steps, the complete trace will be rejected by
|
||||
the emulator as it cannot guarantee the trace to be consistent.
|
||||
@ -23,9 +23,12 @@ markdown_extensions:
|
||||
nav:
|
||||
- index.md
|
||||
- 'User guide':
|
||||
- user/concepts.md
|
||||
- user/installation.md
|
||||
- 'Concepts':
|
||||
- user/concepts/part-model.md
|
||||
- user/concepts/trace-model.md
|
||||
- 'Runtime':
|
||||
- user/runtime/index.md
|
||||
- user/runtime/tracing.md
|
||||
- user/runtime/mark.md
|
||||
- user/runtime/distributed.md
|
||||
|
||||
Loading…
Reference in New Issue
Block a user