PicoCalc plan phase P2, driven by measurements taken on the Lyra as a
paired A/B (git archive HEAD vs the working tree, run side by side
against the same venv).
The headline is the database. Every packet the monitor hears is one
durable commit, and on the SD card each was costing 33.78 ms of fsync.
db._tune() opens in WAL with temp_store=MEMORY: 0.59 ms per commit, a
54x cut. synchronous=NORMAL is requested only once WAL is confirmed
engaged - the pragma returns the mode it settled on rather than raising
when a filesystem refuses it - because under WAL it risks the last
transactions to a power cut, and under the rollback journal it risks the
file itself. This device runs on a battery pack.
Startup: bleak/dbus-fast were already lazy; the real finds were two
cheap *values* dragging heavy subtrees. core/connection.py imports one
constant from core/channels.py, which imported PyCryptodome at module
level (224 ms of CPU-feature probing per run) - now deferred into the
two functions that decrypt. And tools/map.py's register_cli, which runs
for every tool at boot, reached into ui/map_screen.py for a --fraction
default, dragging the basemap's urllib.request -> http.client -> ssl
behind it; DEFAULT_VIEW_FRACTION moves to core/geo.py (pure arithmetic,
already on the boot path) and is re-exported so existing importers are
untouched. 26 modules and 316 ms of import self-time gone.
Per-frame: the corner glow only ever recolours truecolor foregrounds, so
on a 16-slot console it scanned every line of every frame to hand back
the identical list - skipped outright where effects are off, along with
the battery blink and the braille spinner cycle. _has_wide_glyph answers
from the platform when no emoji can be drawn instead of scanning the
composed frame (6.5-9.1 ms per repaint on its own). The header built its
segments twice to measure the compact separator, on exactly the narrow
terminals that take that branch every frame; it now builds once and
measures arithmetically. Together: 101.2 -> 73.2 ms per frame at 53x26,
151.8 -> 110.4 at 53x40, and 72x24 unregressed at 91.7.
That finally gave numbers to set the clocks against. refresh_interval
becomes per-platform tick_s (2.0 s on picocalc: a 1 Hz idle tick alone
was 7-11% of a core doing nothing, and only the header's per-minute
pulse drifts, since screens push their own repaints via invalidate).
The 0.12 s spinner was untenable - 84% of a core at 53x26, and at 53x40
it did not fit in its own interval at all. Five duplicate
_SPINNER_INTERVAL = 0.12 constants across the UI collapse into one
platform-aware spinner_interval() beside the Spinner it paces.
The header refactor was verified equivalent over 540 renders, plain text
and style spans both. The span check earned its keep: the first cut
passed style= to the Text constructor, which makes it the object's base
style and blankets everything appended after, so the version string
would have rendered brand-under-muted. test_header.py only asserted on
.plain and never saw it; it now pins the styling too.
tests/test_performance.py pins each contract as behaviour rather than
timing, including a subprocess guard that fails if Crypto, the network
stack, or the map screen ever creep back onto the startup import graph.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Jean-Pierre MartineauandClaude Opus 5
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