Glossary¶

Terms used throughout these docs. HEP/Key4hep terms are defined as k4Bench uses them, not exhaustively.

Ablation: Removing a subdetector from the geometry to measure its cost by difference. The mechanism behind the full sweep. Approximate, because removing material changes shower development.
at_location: A region-timing attribution view: stepping time charged to the detector the step is physically in. Contrast by_birth.
Attribution: Assigning measured time to a subdetector. The region plugin attributes to the top-level DD4hep DetElement a step belongs to.
Baseline: A run with the full, unmodified geometry, labelled baseline_all. The reference point for all comparisons.
by_birth: A region-timing attribution view: stepping time charged to the detector where the track was created. Secondaries inherit their parent's birth detector. The gap from at_location separates intrinsic from imported cost.
Compact XML: DD4hep's geometry description format. A top-level file pulls in others via <include ref="...">; detectors are <detector name="..."> elements.
CVMFS: The CernVM File System — a read-only, globally distributed filesystem that serves the Key4hep software and geometries (/cvmfs/...). Its read-only nature is why k4Bench patches geometries into temp files.
ddsim: The DD4hep command-line simulation driver (Geant4 under the hood). The program k4Bench benchmarks. k4Bench injects only --compactFile, --numberOfEvents, --outputFile; everything else is yours.
DD4hep: Detector Description for High Energy Physics — the geometry/description toolkit underpinning the simulations k4Bench measures.
DDG4: DD4hep's Geant4 integration layer. The C++ timing plugins are DDG4 actions (event/stepping/tracking) loaded into ddsim.
DetElement: A DD4hep detector-element node. The top-level DetElements (children of the world) are k4Bench's unit of per-detector attribution — the same notion of "subdetector" the sweep uses.
EDM4hep: The common HEP event data model. ddsim writes EDM4hep ROOT files; k4Bench records only the output file's size.
EOS: CERN's large-scale disk storage. Nightly results are uploaded under /eos/user/j/jbeirer/k4bench/... and served to the dashboard over HTTPS (WebEOS).
Event 0 / warmup event: The first simulated event, consistently slower (cold caches, lazy init). Excluded by convention from summary statistics. See Analysis → warmup.
--ddsim-args: The single quoted string of arguments k4Bench forwards verbatim to ddsim. All physics configuration lives here.
Include tree: The graph of XML files reachable from the top-level compact file via <include ref>. Resolved by resolve_includes.
Key4hep: The common turnkey software stack for future-collider experiments, providing ddsim, DD4hep, ROOT, and the Python packages k4Bench depends on.
Orphaned plugin: A DD4hep <plugin> left referencing a detector that was removed during patching. k4Bench heuristically deletes plugins whose <argument value> names a removed detector. See Geometry patching.
Patching: Producing temporary, modified copies of a geometry (detectors removed/kept) without touching the originals. The patcher.
rdtscp: An x86_64 instruction reading the CPU timestamp counter, used by the region plugin as a low-overhead timer (falls back to steady_clock elsewhere).
RSS: Resident Set Size — the physical memory a process holds. Peak RSS (from time -v) is k4Bench's memory metric; the event plugin also samples it per event.
RunResult: The dataclass holding one run's metrics; serialised to the results CSV. See results.model.
Sample: In the nightly CI, a named physics configuration for a detector (e.g. single_e-_10GeV, p8_ee_Zbb_ecm91). Becomes a directory in the EOS layout.
Stack / release: A dated Key4hep release (e.g. key4hep-2026-04-08). The dashboard aligns trends on the release date.
Subdetector: A <detector> in the geometry; the unit k4Bench adds/removes and attributes cost to. Used interchangeably with "detector" here.
Sweep: A set of runs that vary the geometry. See Sweep modes.
/usr/bin/time -v: GNU time's verbose mode, which prints wall time, peak RSS, CPU times, page faults, and context switches. k4Bench wraps ddsim in it and parses the output.
WebEOS: The HTTPS front-end exposing the EOS results directory to the dashboard as an Apache-style listing, discovered/downloaded by dashboard/remote.py.