Real-Time Task Model Inference

This package provides Python reference implementations of the real-time task model inference algorithms used by the Linux Real-Time Model Extractor (LiME).

Implemented Algorithms

The library implements all arrival-model inference algorithms used by LiME.

For certain (i.e., exact) release times:

• infer_sporadic_model: infer the minimum separation parameter of the sporadic task model from a sequence of releases.
• infer_delta_min: infer delta-min curves from a sequence of releases, to be used with max_releases to derive upper bounds on the maximum number of releases in any interval of a given length
• infer_delta_max: infer delta-max curves from a sequence of releases, to be used with min_releases to derive lower bounds on the minimum number of releases in any interval of a given length
• infer_periodic_model: infer periodic (offset, period, jitter) models from a sequence of releases.

For uncertain release windows:

• infer_delta_min_hi / infer_delta_min_lo: infer under-/over-approximations of delta-min from a sequence of release windows (can be used with max_releases).
• infer_delta_max_hi / infer_delta_max_lo: under-/over-approximations of delta-max from a sequence of release windows (can be used with min_releases).
• infer_certain_fit_periodic_model: infer a periodic model from a sequence of release windows that fully covers every release window.
• infer_possible_fit_periodic_model: infer a periodic model from a sequence of release windows that intersects every release window.

The above-mentioned APIs are "one-shot" procedures, consuming all given input in one go and producing a model as a result. Additionally, the library provides streaming extractor variants of all these algorithms, which consume input continuously and can be queried at any time to obtain the model inferred so far. The streaming extractor classes can be imported from rt_model_inference.extractors and are named as follows:

• SporadicExtractor
• DeltaMinExtractor, DeltaMinHiExtractor, and DeltaMinLoExtractor
• DeltaMaxExtractor, DeltaMaxHiExtractor, and DeltaMaxLoExtractor
• PeriodicExtractor, CertainFitPeriodicExtractor, and PossibleFitPeriodicExtractor

Attribution

When using these algorithms for academic work, please cite the following two papers:

1. B. Brandenburg, C. Courtaud, F. Marković, and B. Ye, “LiME: The Linux Real-Time Task Model Extractor”, Proceedings of the 31st IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2025), May 2025.
2. B. Ye, F. Marković, and B. Brandenburg, “Framework-Agnostic Model Inference for Intra-Thread Real-Time Tasks“, Proceedings of the 32nd IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2026), May 2026.

Usage

The algorithms assume a discrete-time model, so all time values passed to the library must be integers. The library provides Instant and Duration in rt_model_inference.time, which are both aliases of int.

from rt_model_inference.time import Instant, Duration

Arrival Model Inference from Exact Release Times

Consider a sequence of observed exact release times:

RELEASES: list[Instant] = [135, 249, 354, 473, 526, 657, 729, 823, 935, 1041, 1144, 1258, 1368, 1434, 1534, 1653, 1753, 1834, 1944, 2057]

Periodic Models

A periodic model explaining all releases can be recovered with infer_periodic_model():

from rt_model_inference import infer_periodic_model, PeriodicModel

pm = infer_periodic_model(RELEASES)

assert isinstance(pm, PeriodicModel)
assert pm.offset == 123
assert pm.period == 100
assert pm.jitter == 50

The corresponding streaming extractor PeriodicExtractor can be given the input piecemeal and allows querying the model extracted so far:

from rt_model_inference.extractors import PeriodicExtractor

ex = PeriodicExtractor()

# process the first 3 observations
ex.feed(RELEASES[:3])

# query the current model estimate based on the input seen so far
cm = ex.current_model
assert isinstance(cm, PeriodicModel)
assert cm.offset == 134
assert cm.period == 110
assert cm.jitter == 5

# consume the rest of the observations
ex.feed(RELEASES[3:])

# final model is the same as the one obtained by infer_periodic_model()
cm = ex.current_model
assert isinstance(cm, PeriodicModel)
assert cm.offset == 123
assert cm.period == 100
assert cm.jitter == 50

Sporadic Models

The classic sporadic task model's scalar minimum-release separation can be obtained with infer_sporadic_model():

from rt_model_inference import infer_sporadic_model

min_sep = infer_sporadic_model(RELEASES)

assert isinstance(min_sep, Duration)
assert min_sep == 53

The functions infer_delta_min() and infer_delta_max() characterize the given release sequence with arrival curves. Arrival curves are represented as delta-min and delta-max vectors (of type list[Duration]). Both infer_delta_min() and infer_delta_max() take an optional keyword parameter nmax controlling the length of the extracted delta-min/max prefix.

from rt_model_inference import infer_delta_min, infer_delta_max

dmin = infer_delta_min(RELEASES, nmax=5)
assert isinstance(dmin, list) and all(isinstance(dmin[i], Duration) for i in range(len(dmin)))
assert dmin == [0, 1, 54, 167, 257, 351]

dmax = infer_delta_max(RELEASES, nmax=5)
assert isinstance(dmax, list) and all(isinstance(dmax[i], Duration) for i in range(len(dmax)))
assert dmax == [130, 223, 337, 434, 544, 638]

The extracted delta-min and delta-max vectors can be interpreted with max_releases() and min_releases(), respectively.

from rt_model_inference import max_releases, min_releases

# In any interval of length 100, at least 0 and at most 2 releases are observed.
assert min_releases(dmax, 100) == 0
assert max_releases(dmin, 100) == 2

# In any interval of length 300, at least 2 and at most 4 releases are observed.
assert min_releases(dmax, 300) == 2
assert max_releases(dmin, 300) == 4

The corresponding streaming extractors are SporadicExtractor, DeltaMinExtractor, and DeltaMaxExtractor:

from rt_model_inference.extractors import SporadicExtractor, DeltaMinExtractor, DeltaMaxExtractor

ex_sp = SporadicExtractor()
ex_sp.feed(RELEASES)
assert ex_sp.current_model == min_sep

ex_min = DeltaMinExtractor(nmax=5)
ex_min.feed(RELEASES)
assert ex_min.current_model == dmin

ex_max = DeltaMaxExtractor(nmax=5)
ex_max.feed(RELEASES)
assert ex_max.current_model == dmax

Arrival Model Inference from Uncertain Release Windows

Suppose that instead of exact release-time observations, we only have the following release-window observations:

from rt_model_inference.time import ReleaseWindow

RELEASE_WINDOWS: list[ReleaseWindow] = [(117, 145), (242, 277), (332, 356), (454, 489), (505, 554), (642, 666), (728, 732), (818, 846), (933, 949), (1020, 1066), (1131, 1161), (1255, 1259), (1342, 1379), (1419, 1446), (1511, 1536), (1647, 1654), (1743, 1763), (1812, 1857), (1919, 1965), (2049, 2068)]

Periodic Models

Certain-fit and possible-fit periodic models can be extracted with infer_certain_fit_periodic_model() and infer_possible_fit_periodic_model(), respectively:

from rt_model_inference import infer_certain_fit_periodic_model, infer_possible_fit_periodic_model

cf = infer_certain_fit_periodic_model(RELEASE_WINDOWS)

assert isinstance(cf, PeriodicModel)
assert cf.offset == 105
assert cf.period == 100
assert cf.jitter == 84

pf = infer_possible_fit_periodic_model(RELEASE_WINDOWS)

assert isinstance(pf, PeriodicModel)
assert pf.offset == 132
assert pf.period == 100
assert pf.jitter == 23

The certain-fit model conservatively over-approximates the ground-truth model (lower offset, larger jitter), whereas the possible-fit under-approximates the ground-truth model (larger offset, lower jitter).

The corresponding streaming extractors are CertainFitPeriodicExtractor and PossibleFitPeriodicExtractor:

from rt_model_inference.extractors import CertainFitPeriodicExtractor, PossibleFitPeriodicExtractor

ex_cf = CertainFitPeriodicExtractor()
ex_cf.feed(RELEASE_WINDOWS)
assert ex_cf.current_model == cf

ex_pf = PossibleFitPeriodicExtractor()
ex_pf.feed(RELEASE_WINDOWS)
assert ex_pf.current_model == pf

Sporadic Models

Over- and under-approximations of delta-min and delta-max vectors can be obtained with infer_delta_min_hi(), infer_delta_min_lo(), infer_delta_max_hi(), and infer_delta_max_lo(). For example:

dmin_hi = infer_delta_min_hi(RELEASE_WINDOWS, nmax=5)

assert isinstance(dmin_hi, list) and all(isinstance(dmin_hi[i], Duration) for i in range(len(dmin_hi)))
assert dmin_hi == [0, 1, 17, 133, 229, 330]
assert max_releases(dmin_hi, 100) == 2
assert max_releases(dmin_hi, 300) == 4

dmax_lo = infer_delta_max_lo(RELEASE_WINDOWS, nmax=5)

assert isinstance(dmax_lo, list) and all(isinstance(dmax_lo[i], Duration) for i in range(len(dmax_lo)))
assert dmax_lo == [160, 255, 371, 453, 560, 655]
assert min_releases(dmax_lo, 100) == 0
assert min_releases(dmax_lo, 300) == 2

The extracted delta-min-hi vector safely over-approximates the ground-truth delta-min vector, and the extracted delta-max-lo vector safely under-approximates the ground-truth delta-max vector.

The corresponding streaming extractors are DeltaMinHiExtractor, DeltaMinLoExtractor, DeltaMaxHiExtractor and DeltaMaxLoExtractor. For example:

ex_dmin_hi = DeltaMinHiExtractor(nmax=5)
ex_dmin_hi.feed(RELEASE_WINDOWS)
assert ex_dmin_hi.current_model == dmin_hi

ex_dmax_lo = DeltaMaxLoExtractor(nmax=5)
ex_dmax_lo.feed(RELEASE_WINDOWS)
assert ex_dmax_lo.current_model == dmax_lo

The above examples are all checked in tests/test_examples.py. See also the other unit tests for further usage examples.

Development

We recommend using the uv package manager for Python.

Quick Start

Install all dependencies with the uv package manager:

uv sync

Running the Package's CLI

The library provides a small CLI, mainly for testing and demonstration purposes.

To run the CLI, use the standard module entry point:

uv run python -m rt_model_inference --help

The CLI reads release times from stdin by default (or from a file path argument):

• if there is one number per line, the value is interpreted as a (certain) release time;
• if there are two numbers per line, the two values are interpreted as defining an (uncertain) release window.

To exercise periodic inference with generated sample input:

seq 27 30 1000 | uv run python -m rt_model_inference -m periodic --json

To apply the CLI tool to one of the CSV files in tests/traces/periodic or tests/traces/sporadic, use awk to convert the input to the expected format.

With release windows:

awk -F, '{print $2 " " $3}'  tests/traces/periodic/rust-p-10task_u30_mu22_ms_v13_task=07_period=16000000.csv | uv run python -m rt_model_inference -m periodic-certain-fit --json

Exact release times:

awk -F, '{print $1}'  tests/traces/periodic/rust-p-10task_u30_mu22_ms_v13_task=07_period=16000000.csv | uv run python -m rt_model_inference -m periodic --json

Exercise the streaming extractors:

awk -F, '{print $2 " " $3}'  tests/traces/sporadic/cpp-ar-mixed_20task_u90_mu22_ms_v22_task=05.csv | uv run python -m rt_model_inference -m delta-min-hi --n-max 10 --stream 25

awk -F, '{print $2 " " $3}'  tests/traces/sporadic/cpp-ar-mixed_20task_u90_mu22_ms_v22_task=05.csv | uv run python -m rt_model_inference -m delta-max-lo --n-max 10 --stream 25

Run the Tests

Run the standard tests:

uv run pytest -n auto

To run tests on all traces included in the repository, set the TEST_ALL_TRACES environment variable.

TEST_ALL_TRACES=1 uv run pytest -n auto

Linter and Type Checking

This package uses type annotations and the ruff linter.

Run ruff:

uvx ruff check

Check all types:

uvx basedpyright

Both should report no issues.

License

This library is free software and released under the MIT license.

Feedback, Questions, Patches

Please use the project's GitLab issue tracker or contact Björn Brandenburg.

A Github mirror is available for those who prefer Github.