trace-v3 #7
@ -13,9 +13,8 @@ The ovni project implements a fast instrumentation library that records
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small events (starting at 12 bytes) during the execution of programs to
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later investigate how the execution happened.
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<!-- FIXME: Add a index for runtime -->
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The instrumentation process is split in two stages:
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[runtime](user/runtime/tracing.md)
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[runtime](user/runtime/index.md)
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tracing and [emulation](user/emulation/index.md).
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During runtime, very short binary events are stored on disk which
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@ -4,7 +4,7 @@ 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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![lalala](part-model.svg "foo bar")
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![Part model](part-model.svg)
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Notice how a loom can restrict the CPUs of the node to its child processes.
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@ -15,14 +15,12 @@ To initialize libovni follow these steps in all threads:
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ovni function. It can be called multiple times from any thread, but only one
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is required.
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2. **Init the process**. Call `ovni_proc_init()` to initialize the process when
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a new process begins the execution. It can only be called **once per
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process** and it must be called before the thread is initialized.
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2. **Init the process**. Call `ovni_proc_init()` to initialize the process. It
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can only be called **once per process** and it must be called before the
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thread is initialized.
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3. **Init the thread**. Call `ovni_thread_init()` when a new thread begins the
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execution (including the main process thread after the process is
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initialized). Multiple attempts to initialize the thread are ignored with a
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warning.
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3. **Init the thread**. Call `ovni_thread_init()` to initialize the thread.
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Multiple attempts to initialize the same thread are ignored with a warning.
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The `ovni_proc_init()` arguments are as follows:
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@ -32,8 +30,8 @@ void ovni_proc_init(int app, const char *loom, int pid);
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The `app` defines the "appid" of the program, which must be a number >0. This is
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useful to run multiple processes some of which run the same "app", so you can
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tell which one is which. The `loom` defines the
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[loom](../concepts/part-model.md#loom) name and assignes the process to that
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tell which one is which. The `loom` argument defines the
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[loom](../concepts/part-model.md#loom) name and maps the process to that
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loom. It must be compose of the host name, a dot and a suffix. The PID is the
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one obtained by `getpid(2)`.
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@ -59,8 +57,8 @@ the thread stream.
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## Start the execution
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The current thread must switch to the "Running" state before any event can be
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processed by the emulator. Do so by emitting a `OHx` event in the stream with
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the appropriate payload:
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processed by the emulator. Do so by emitting a [`OHx`
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event](../emulation/events.md#OHx) in the stream with the appropriate payload:
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```c
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static void thread_execute(int32_t cpu, int32_t ctid, uint64_t tag)
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@ -1,94 +0,0 @@
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# Tracing a new program
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Read carefully this document before using libovni to instrument a new
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component. There are a few rules you must follow to ensure the runtime
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trace is correct.
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## Trace processes and threads
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- Call `ovni_version_check()` once before calling any ovni function.
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- Call `ovni_proc_init()` when a new process begins the execution.
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- Call `ovni_thread_init()` when a new thread begins the execution
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(including the main process thread).
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- Call `ovni_thread_require()` with the required model version before
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emitting events for that model.
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- Call `ovni_flush()` and `ovni_thread_free()` when it finishes (in that
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order).
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- Call `ovni_proc_fini()` when a process ends, after all threads have
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finished.
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You can use `ovni_ev_emit()` to record a new event. If you need more
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than 16 bytes of payload, use `ovni_ev_jumbo_emit()`. See the [trace
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specification](trace_spec.md) for more details.
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Compile and link with libovni. When you run your program, a new
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directory ovni will be created in the current directory `$PWD/ovni`
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which contains the execution trace.
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You can change the trace directory by defining the `OVNI_TRACEDIR`
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environment variable. The envar accepts a trace directory name, a
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relative path to the trace directory, or its absolute path. In the
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first case, the trace directory will be created in the current
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directory `$PWD`.
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## Rules
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Follow these rules to avoid losing events:
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1. No event may be emitted until the process is initialized with
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`ovni_proc_init()` and the thread with `ovni_thread_init()`.
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2. When a thread ends the execution, it must call `ovni_flush()` to write the
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events in the buffer to disk.
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3. All threads must have flushed its buffers before calling `ovni_proc_fini()`.
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## Select a fast directory
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During the execution of your program, a per-thread buffer is kept where the new
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events are being recorded. When this buffer is full, it is written to disk and
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emptied, an operation known as flush. This may take a while depending on the
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underliying filesystem.
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Keep in mind that the thread will be blocked until the flush ends, so if your
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filesystem is slow it would interrupt the execution of your program for a long
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time. It is advisable to use the fastest filesystem available (see the tmpfs(5)
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and df(1) manual pages).
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You can select the trace directory where the buffers will be flushed during the
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execution by setting the environment variable `OVNI_TMPDIR`. The last directory
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will be created if doesn't exist. In that case, as soon as a process calls
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`ovni_proc_fini()`, the traces of all its threads will be moved to the final
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directory at `$PWD/ovni`. Example:
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OVNI_TMPDIR=$(mktemp -u /dev/shm/ovni.XXXXXX) srun ./your-app
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To test the different filesystem speeds, you can use hyperfine and dd. Take a
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closer look at the max time:
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```
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$ hyperfine 'dd if=/dev/zero of=/gpfs/projects/bsc15/bsc15557/kk bs=2M count=10'
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Benchmark 1: dd if=/dev/zero of=/gpfs/projects/bsc15/bsc15557/kk bs=2M count=10
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Time (mean ± σ): 71.7 ms ± 130.4 ms [User: 0.8 ms, System: 10.2 ms]
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Range (min … max): 14.7 ms … 1113.2 ms 162 runs
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Warning: Statistical outliers were detected. Consider re-running this
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benchmark on a quiet PC without any interferences from other programs. It
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might help to use the '--warmup' or '--prepare' options.
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$ hyperfine 'dd if=/dev/zero of=/tmp/kk bs=2M count=10'
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Benchmark 1: dd if=/dev/zero of=/tmp/kk bs=2M count=10
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Time (mean ± σ): 56.2 ms ± 5.7 ms [User: 0.6 ms, System: 14.8 ms]
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Range (min … max): 45.8 ms … 77.8 ms 63 runs
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$ hyperfine 'dd if=/dev/zero of=/dev/shm/kk bs=2M count=10'
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Benchmark 1: dd if=/dev/zero of=/dev/shm/kk bs=2M count=10
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Time (mean ± σ): 11.4 ms ± 0.4 ms [User: 0.5 ms, System: 11.1 ms]
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Range (min … max): 9.7 ms … 12.5 ms 269 runs
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```
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|
@ -29,7 +29,6 @@ nav:
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- user/concepts/trace-model.md
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- 'Runtime':
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- user/runtime/index.md
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- user/runtime/tracing.md
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- user/runtime/mark.md
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- user/runtime/distributed.md
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- user/runtime/kernel.md
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|
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