CPU benchmarks

The current comparison, measured on 2026-09-14, runs ALH 1.2.35 and QtALH against the same private IOC with X11 rendering. QtALH uses less CPU while idle and during updates without logging; ALH uses less CPU when file logging is enabled.

Results

Values are medians of five alternating trials per application and workload. 100% means one fully occupied CPU core. Application CPU includes its threads and excludes the IOC, X server, CA repeater, and validation monitor.

Workload	Trial duration	ALH CPU	QtALH CPU	QtALH versus ALH
Main window, idle	10 s	0.9999%	0.5000%	50.0% lower
Updates, logging disabled	10 s	3.6998%	2.4998%	32.4% lower
Updates, logging enabled	30 s	3.2666%	4.7666%	45.9% higher

Workload	ALH range	QtALH range
Idle	0.8999–1.0999%	0.4000–0.5000%
Updates, logging disabled	3.1998–3.8998%	2.3999–2.6999%
Updates, logging enabled	3.1999–3.5000%	4.5999–4.9666%

Each direction holds in all five paired rounds, with non-overlapping observed ranges. The logged difference is 1.5000 percentage points of one core. These are controlled local measurements, not a formal statistical significance test or a performance guarantee for other installations.

ALH and QtALH divide rendering work differently between the application and X11. Including the dedicated Xvfb process preserves the same ranking:

Workload	ALH + Xvfb CPU	QtALH + Xvfb CPU
Idle	0.9999%	0.5000%
Updates, logging disabled	3.7998%	2.5999%
Updates, logging enabled	3.4333%	4.9332%

These are medians of per-trial totals, not sums of separate medians. The raw CSV also records Xvfb CPU separately. Small or zero readings are limited by Linux clock-tick resolution; this virtual display does not measure a desktop compositor or GPU-backed rendering. Workloads use different trial durations, so comparisons between rows do not isolate the marginal cost of enabling logging. Raw trials.

Workload and environment

• 1,000 channels in ten groups; active records alternate normal/MAJOR every 0.5 seconds, nominally 2,000 transitions/second.
• Global acknowledgement mode, muted sound, default legacy appearance, and 1000×600 main windows. QtALH also displays its default 220×35 runtime indicator; ALH does not display an equivalent separate runtime window with -mainwindow.
• Three-second warmup before timing. Each trial starts a fresh application; logged trials use fresh directories and the default 2,000-record circular log. Printer/database helpers are not configured.
• Private 1600×1000×24 Xvfb display, isolated Qt settings, and loopback-only CA discovery. IOC records use PINI=YES, idle CALC=0, and active CALC=10-VAL.
• Intel Core i7-12700, Linux x86-64, GCC 11.5.0, Qt 5.15.9, EPICS Base 7.0.8, the existing powersave governor, ALH -O2 -g -Wall -std=gnu99, and QtALH -O2 -g -Wall -Wextra -std=c++17 -fPIC builds.
• The application uses logical CPU 2, IOC CPU 6, Xvfb CPU 10, and repeater/monitor CPU 14. These map to physical cores 1, 3, 5, and 7 on this host. Affinity is set before launch, inherited by new threads, and checked on the main thread after warmup. The cores are not exclusively reserved; other host activity and CPU frequency are not fixed.

Idle, updates, and logged updates run in that order. Trials 1/3/5 run ALH first; trials 2/4 run QtALH first. No builds, test suites, or profilers run alongside timing. Window inspection runs after the CPU measurement endpoints. Linux process accounting has about 0.1 percentage-point resolution over ten seconds and 0.033 over thirty seconds.

QtALH analytics remains attached, with no open analytics dashboard or configured notification subscriptions. Other layouts, channel counts, fonts, filtering modes, operator interactions, and deployment platforms can change CPU use. The logged comparison retains each application's existing persistence behavior; see logging implementation.

Validation

All 30 measured runs passed. Every active trial produced both normal and MAJOR root-severity outputs during timing: 20 changes per unlogged trial and 60 per logged trial. Each logged run retained exactly 2,000 lines containing both states for every one of the 1,000 channels. Logging-disabled runs produced no alarm or operation files. Application diagnostic logs were empty.

These checks verify aggregate processing and retained per-channel states; they do not count every callback or prove zero event loss. Startup, graceful shutdown, and crash-recovery durability are outside the timed workload. The applications are terminated with SIGTERM after measurement. The same QtALH build also passed 98 IOC integration checks; see the test guide for coverage.

Measured builds

The source base at measurement was c7b67219cd451d92a8df9bb60b8d5993890a2622. ALH source was unchanged. QtALH additionally included the snapshot metadata cache, bounded text-width cache, unused alarm-log formatting bypass, and legacy runtime-font fix. SHA-256 identifies the exact executables measured:

alh 526082cfd1a9303c74da4baf8b393383a7ed30d0f16b765f60a43b2963d5291d
qtalh 5cb366f78bc74ecbfb53702d7e811c65fac6b7110e9ccf571d55d7e62b2738d3

Reproduction

The IOC benchmark accepts executable paths, EPICS tool paths, and CPU assignments on the command line. It requires Linux /proc, Python 3, stdbuf, and EPICS softIoc, caRepeater, caget, caput, and camonitor. --xvfb additionally requires Xvfb and xwininfo; --cpus requires taskset and four allowed CPUs on distinct physical cores. Check lscpu -e=CPU,CORE,SOCKET before choosing CPUs on another host.

make -C alh EPICS_BASE=/path/to/epics/base
make -C qtalh QT_VERSION=5 EPICS_BASE=/path/to/epics/base
python3 qtalh/tests/benchmark_ioc.py \
  bin/Linux-x86_64/alh bin/Linux-x86_64/qtalh --labels alh qtalh \
  --epics-bin /path/to/epics/base/bin/linux-x86_64 \
  --xvfb --cpus 2 6 10 14 --channels 1000 --max-records 2000 \
  --seconds 10 --logged-seconds 30 --trials 5 \
  --output /tmp/alh-vs-qtalh-repeat

Use the same options for the published workload, adjusting executable/EPICS paths and CPU assignments for the target host. The tool uses global mode and muted sound for both applications. --modes idle updates logged-updates selects the workloads, which are all enabled by default. Log capacity must allow at least two records per channel so every channel's normal and MAJOR states can be checked.

CSV is written to stdout. --output must name a new directory and retains the CSV, configuration, executable hashes, commands, logs, window trees, and validation records for that run. Without it, temporary evidence is removed on exit. These local run artifacts do not need to be committed alongside the published CSV. The runner stops the processes it owns on completion, failure, or interruption.

Without --cpus, processes inherit the caller's affinity. Without --xvfb, set DISPLAY or QT_QPA_PLATFORM yourself; X-server CPU fields are then empty (unavailable). Use X11 when comparing with Motif ALH. Offscreen rendering is suitable only for QtALH comparisons and does not reproduce the published workload.

For isolated QtALH engine/UI investigations, the separate in-process harness supports idle, updates, filtered, and runtime workloads:

make -C qtalh QT_VERSION=5 benchmark-cpu
QT_QPA_PLATFORM=offscreen qtalh/O.Linux-x86_64-qt5/benchmark_cpu 10000 updates 10

This harness verifies delivered events and final channel/root state. It does not include Channel Access or run ALH; use the complete-application runner for the published comparison.