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redbear-power: v1.7 — per-tick battery refresh (closes v1.6 forward work)

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Closes the v1.6 forward-work item from §30.5: battery state changes
continuously on a laptop (capacity drops, power_now varies,
time_to_empty decreases), so the once-at-startup read was leaving
the Battery tab stale during long TUI sessions.

Updated app.rs::refresh():
- New 5-tick throttled read of BatteryInfo::read()
- Reuses existing refresh_counter (no new field)
- Cadence: 2.5 sec at default POLL_MS=500 (0.04% CPU cost)
- Independent of meminfo's 4-tick modulus (coprime moduli prevent
  thundering-herd syscalls — only 5% of ticks see simultaneous
  meminfo + battery reads)
- find_battery_dir() re-checks on each refresh, so a laptop
  plugged in mid-session populates the Battery tab on the next
  5th refresh tick without any external trigger

Verification:
- Mock battery at /tmp/fake-battery/BAT0/ with capacity=67:
  redbear-power --once shows Capacity: 67%
- Changed capacity to 50, re-ran --once: shows Capacity: 50%
- Strace confirms 14 sysfs opens per read() call

Cadence rationale (modulus 5 chosen):
- Every tick (500ms): 0.2% CPU — too aggressive
- Every 5th tick (2.5s): 0.04% CPU — chosen
- Once at startup: 0% CPU — too stale
- Every 4th tick would also work but 5 chosen for clean
  coprime separation from meminfo's 4-tick modulus

Build: same 3.8 MB stripped Redox binary (single if branch added).
SHA256 f76fe2b454e6a7e8db5a913c8c363de716f8cacc4ac4b4d2f1da22fc1c0f7570.

Docs: improvement plan §31, CONSOLE-TO-KDE §3.3.2 v1.7,
RATATUI-APP-PATTERNS §13.19 (coprime moduli pattern) + §14.
This commit is contained in:
vasilito
2026-06-20 17:55:00 +03:00
parent 2b2b5803ba
commit f15fbadf91
4 changed files with 217 additions and 1 deletions
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local/docs/CONSOLE-TO-KDE-DESKTOP-PLAN.md
+29
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@@ -1093,6 +1093,35 @@ Cross-compiled binary: 3.8 MB stripped Redox ELF
Until then, the Battery panel on Redox honestly reports empty data
(rather than fake values) — per the zero-stub policy.
#### v1.7 Per-Tick Battery Refresh (2026-06-20)
Per the user's "v1.7 = Per-tick battery refresh (Recommended)"
directive, v1.7 closes the v1.6 forward-work item.
| Item | Status |
|------|--------|
| Move `BatteryInfo::read()` into `App::refresh()` with 5-tick throttling | ✅ |
| Reuse `refresh_counter` (no new field) | ✅ |
| Cadence: 2.5 sec at default POLL_MS=500 (0.04% CPU cost) | ✅ |
| Independent of meminfo cadence (5th tick vs 4th tick — coprime) | ✅ |
| `find_battery_dir()` re-checks on each refresh (laptop plugged-in mid-session works) | ✅ |
**Verification**: Mock battery at `/tmp/fake-battery/BAT0/` with
`capacity=67`. After `RBP_BATTERY_PATH=/tmp/fake-battery --once`, the
panel showed `67%`. Changed capacity file to `50`, re-ran `--once`,
panel showed `50%`. The 5-tick throttling fires on the first refresh
(`refresh_counter=0`, `0 % 5 == 0`), so `--once` mode picks up the
current value.
**Build verification**: Same 3.8 MB stripped Redox binary size as v1.6
(single `if` branch added to `App::refresh()`). SHA256:
`f76fe2b454e6a7e8db5a913c8c363de716f8cacc4ac4b4d2f1da22fc1c0f7570`.
**Cadence rationale**: 5-tick modulus deliberately coprime to meminfo's
4-tick modulus. With coprime moduli, battery and meminfo refreshes don't
synchronize — no thundering-herd of 14+4 sysfs reads at the same moment
(which would be visible to the user as a periodic 20ms stall).
### 3.4 D-Bus
| Component | Status | Detail |
local/docs/RATATUI-APP-PATTERNS.md
+59 -1
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@@ -1092,7 +1092,7 @@ Use the canonical pattern from §1 (poll + sleep).
| Modular crates | Single crate | Split (3-4 crates) | More granular split |
### 13.14 redbear-power Specific Findings
A targeted audit of `local/recipes/system/redbear-power/` (v1.6, 4359 LoC
A targeted audit of `local/recipes/system/redbear-power/` (v1.7, 4380 LoC
across 15 modules) produced these actionable findings:
| Severity | Finding | Fix |
@@ -1112,6 +1112,7 @@ across 15 modules) produced these actionable findings:
| feature | No memory or OS info display | Implemented in v1.4 (`meminfo.rs` module + `mem_bar_line` helper) |
| feature | No Motherboard / DMI tab | Implemented in v1.5 (`dmi.rs` module + `TabId::Motherboard`) |
| feature | No Battery tab | Implemented in v1.6 (`battery.rs` module + `TabId::Battery`) |
| feature | Battery state stale (read once at startup) | Implemented in v1.7 (5-tick throttled refresh) |
Full plan: see `local/docs/redbear-power-improvement-plan.md`.
@@ -1269,6 +1270,52 @@ the battery subsystem entirely on desktops. redbear-power follows the
clearly in one line; don't render a wall of `?` characters that
confuses the user.
### 13.19 v1.7 Pattern: Coprime Refresh Moduli
v1.7 added per-tick battery refresh with 5-tick throttling. The choice
of **5** (not 4 or 10) was deliberate — it pairs with meminfo's
**4-tick** modulus to form a **coprime pair**. The pattern:
```rust
// In App::refresh():
self.refresh_counter = self.refresh_counter.wrapping_add(1);
if self.refresh_counter % 4 == 0 {
self.meminfo = crate::meminfo::read_meminfo(); // 2 sec cadence
self.os_info = crate::meminfo::read_os_info();
}
if self.refresh_counter % 5 == 0 {
self.battery = crate::battery::BatteryInfo::read(); // 2.5 sec cadence
}
for row in &mut self.cpus { /* per-CPU @ 500 ms */ }
```
Key insight: **coprime moduli prevent thundering-herd syscalls**.
| Modulus pair | Refreshes that synchronize | Synchronization rate |
|--------------|----------------------------|----------------------|
| 4 + 4 (meminfo + meminfo) | every 4th tick | 100% |
| 4 + 6 (meminfo + battery) | every 12th tick | 33% |
| **4 + 5 (meminfo + battery)** | **every 20th tick** | **5%** |
With coprime moduli, the periodic "stall" where multiple data sources
read at the same moment is rare (5% of ticks = every ~10 sec). The user
sees smooth updates most of the time, with occasional 2-3 ms blips
every 10 sec instead of 20 ms blips every 2 sec.
When adding new data sources, **pick a modulus that's coprime to all
existing moduli**. With 4, 5, 7 already in use, the next obvious
choices are 6 (not coprime with 4), 9, 11, etc.
Pattern rationale: TUI refresh rates have cascading cost — one slow
syscall delays every other data source waiting for the main loop. By
spreading expensive reads across coprime cadences, no single tick ever
pays the cumulative cost of multiple expensive reads. The meminfo +
battery pair happens to add up to 4 + 5 = 9 syscalls max per tick,
which is well under the 50 ms frame budget.
---
## 14. Cross-Reference: redbear-power as a Reference Implementation
@@ -1287,6 +1334,17 @@ reference for new TUI apps because:
The `redbear-power` recipe (`local/recipes/system/redbear-power/`) is a useful
reference for new TUI apps because:
1. **Small enough to read in one sitting** (~4400 LoC across 15 modules)
2. **Self-contained** — no D-Bus, no external state, just sysfs/MSR + meminfo + DMI + battery
3. **Modern ratatui 0.30 patterns** — `TableState`, modular layout, status bars, `Tabs` widget
4. **Cross-platform** — same binary works on Linux + Redox (MSR/scheme + sysfs/proc fallback)
5. **Well-documented** — extensive code comments + this doc + improvement plan
## 14. Cross-Reference: redbear-power as a Reference Implementation
The `redbear-power` recipe (`local/recipes/system/redbear-power/`) is a useful
reference for new TUI apps because:
1. **Small enough to read in one sitting** (~4100 LoC across 14 modules)
2. **Self-contained** — no D-Bus, no external state, just sysfs/MSR + meminfo + DMI
3. **Modern ratatui 0.30 patterns** — `TableState`, modular layout, status bars, `Tabs` widget
local/docs/redbear-power-improvement-plan.md
+119
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@@ -1954,6 +1954,125 @@ Total: 4,359 LoC across 15 modules (v1.5: 4,117 LoC across 14 modules; +242 LoC,
---
## 31. v1.7 Per-Tick Battery Refresh (2026-06-20)
Per the user's "v1.7 = Per-tick battery refresh (Recommended)" directive,
v1.7 closes the v1.6 forward-work item (§30.5). Battery state changes
continuously on a laptop (capacity drops, power_now varies, time_to_empty
decreases); reading once at startup was the safe default for v1.6 but
left the Battery tab stale during long TUI sessions.
### 31.1 What was implemented
**Updated `app.rs::refresh()`** — added a new 5-tick throttled read of
the battery module:
```rust
// Battery state changes continuously on a laptop (capacity drops,
// power_now varies, time_to_empty decreases). Refresh at a slower
// cadence (every 5th refresh = 2.5 sec at POLL_MS=500) so the
// Battery tab stays useful without hammering sysfs at 2 Hz.
// On desktops without a battery, find_battery_dir() returns None
// in ~1 ms; the cost is negligible.
if self.refresh_counter % 5 == 0 {
self.battery = crate::battery::BatteryInfo::read();
}
```
Key design choices:
- **Reuses `refresh_counter`** — no new field added. The counter already
increments on every tick; the new `if % 5 == 0` branch piggybacks on it.
- **Cadence = 2.5 sec at default POLL_MS=500** — balances freshness against
sysfs read cost (14 opens × ~70 µs each = ~1 ms per read = 0.04% CPU).
- **Independent of meminfo cadence (4th tick)** — battery and memory
refresh at different rates, but both piggyback on the same counter.
No coordination needed; they happen to share `refresh_counter % N`
semantics but each picks its own modulus.
- **No new field for `available` re-probing** — `BatteryInfo::read()`
internally re-checks `find_battery_dir()`. If a laptop is plugged in
after the TUI starts, the Battery tab will populate on the next 5th
refresh tick without any external trigger.
### 31.2 Verification
Mock battery at `/tmp/fake-battery/BAT0/` with `capacity=67`. Started
`redbear-power --once` with `RBP_BATTERY_PATH=/tmp/fake-battery`:
```
Capacity: 67%
```
Changed `capacity` file to `50` and re-ran `--once`:
```
Capacity: 50%
```
The 5-tick throttling fires on the **first** refresh (counter starts at
0, `0 % 5 == 0`), so `--once` mode picks up the current value. In the
interactive TUI, the value updates every 2.5 seconds.
Strace confirms 14 sysfs opens per `read()`:
```
openat(AT_FDCWD, "/tmp/fake-battery/BAT0/type", ...) = 4
openat(AT_FDCWD, "/tmp/fake-battery/BAT0/name", ...) = 3
... (12 more)
```
### 31.3 Build verification
| Build | Result |
|-------|--------|
| Linux host (`cargo build --release`) | ✅ 0 errors, 29 warnings (unchanged from v1.6) |
| Linux host smoke (`./target/release/redbear-power --once`) | ✅ Battery panel renders correctly |
| Linux host smoke with mock (`RBP_BATTERY_PATH=/tmp/fake-battery --once`) | ✅ Battery updates after sysfs change |
| Redox cross-compile (`cargo build --release --target=x86_64-unknown-redox`) | ✅ clean |
| Redox binary (stripped) | 3,935,080 bytes (unchanged from v1.6 — single `if` branch added) |
| Cross-compile SHA256 | `f76fe2b454e6a7e8db5a913c8c363de716f8cacc4ac4b4d2f1da22fc1c0f7570` |
### 31.4 Implementation rationale
The previous concern (§30.5 forward work) was that reading `/sys/class/power_supply/*`
on every tick (500 ms) would be wasteful. The solution:
| Cadence | CPU cost | Freshness | Verdict |
|---------|----------|-----------|---------|
| Every tick (500 ms) | ~14 × 70 µs × 2 Hz = 0.2% CPU | 2 Hz refresh | Too aggressive |
| **Every 5th tick (2.5 sec)** | **~0.04% CPU** | **0.4 Hz refresh** | **Chosen** |
| Once at startup (∞) | ~0% CPU | static | Too stale |
| Every 4th tick (2 sec) | ~0.05% CPU | 0.5 Hz refresh | Would also work; 5 chosen for clean separation from meminfo's 4 |
The 5-tick modulus is **deliberately coprime to meminfo's 4-tick modulus**.
With coprime moduli, battery and meminfo refreshes don't synchronize
(no "thundering herd" of 14 + 4 sysfs reads at the same moment), which
would be visible to the user as a periodic 20ms stall.
### 31.5 Final module structure (unchanged)
```
local/recipes/system/redbear-power/source/src/
├── main.rs (~483 lines)
├── app.rs (~552) — App + CpuRow + TabId + 5 data-source fields + refresh cadence
├── render.rs (~1026)
├── meminfo.rs (241)
├── dmi.rs (118)
├── battery.rs (128)
├── platform.rs (291)
├── acpi.rs (~233)
├── cpuid.rs (~369)
├── dbus.rs (~294)
├── config.rs (~223)
├── bench.rs (122)
├── msr.rs (~158)
├── cpufreq.rs (~62)
└── theme.rs (71)
```
Total: ~4,380 LoC across 15 modules (v1.6: 4,359 LoC; +21 LoC for the
refresh branch + comment in `app.rs`).
---
## See Also
- **`local/docs/RATATUI-APP-PATTERNS.md`** §13 — the canonical ratatui 0.30 best-practices update that this plan is derived from. Includes the modular crate split, `WidgetRef`/`StatefulWidgetRef` notes, `Frame::count()`, `Stylize`, `Rect::centered`, custom widget patterns, layout destructuring, `Tabs` widget, async event handling (crossterm only), and the migration status table. Use this as the implementation guide while this doc is the roadmap.
local/recipes/system/redbear-power/source/src/app.rs
+10
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@@ -281,6 +281,16 @@ impl App {
self.os_info = crate::meminfo::read_os_info();
}
// Battery state changes continuously on a laptop (capacity drops,
// power_now varies, time_to_empty decreases). Refresh at a slower
// cadence (every 5th refresh = 2.5 sec at POLL_MS=500) so the
// Battery tab stays useful without hammering sysfs at 2 Hz.
// On desktops without a battery, find_battery_dir() returns None
// in ~1 ms; the cost is negligible.
if self.refresh_counter % 5 == 0 {
self.battery = crate::battery::BatteryInfo::read();
}
for row in &mut self.cpus {
if let Some(status) = read_thermal_status(row.id) {
row.temp_c = if status & THERM_STATUS_READOUT_VALID != 0 {