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v0.13.22 — replace bisect-on-fail with hysteresis Block↔Single

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The v0.13.21 bisect-on-fail recovery was correct (100% of recoverable
sectors picked up) but slow on dense damage clusters. Live test on
Dune 2 v0.13.21 burned ~30 s per damaged 60-block — paying a ~5 s
kernel ABORT/timeout at every level of a log₂(60) ≈ 6 deep DFS, on
the failing branch each time.

Replaced with a two-state hysteresis machine in Disc::copy:

  Block(batch):
    read(batch) ok    → write, advance, stay Block
    read(batch) fail  → switch to Single, retry SAME range at bpt=1

  Single:
    read(1) ok    → write, consecutive_good++
                    if consecutive_good >= BPT1_EXIT_THRESHOLD:
                      switch to Block, reset counter
    read(1) fail  → mark NonTrimmed, consecutive_good = 0

BPT1_EXIT_THRESHOLD = 10_000 sectors (= 20 MB clean run). Calibrated
from the 2026-04-26 BU40N empirical probe data; tunable.

Per-block math on a damaged 60-block with 1 truly bad sector:

  Bisect      (v0.13.21): ~30 s  (5 s × 6 levels)
  Hysteresis  (v0.13.22): ~10 s  (5 s bpt=batch fail
                                  + 59 × 1 ms good
                                  + 1 × 5 s bad)

Inside a damaged cluster spanning many 60-blocks the win compounds:
hysteresis pays the bpt=batch fail cost ONCE on entry, then stays at
bpt=1 across the cluster; bisection re-paid it every 60 sectors. For
Dune 2's ~1248-sector boundary cluster that's ~21 fewer 5-sec
kernel timeouts ≈ 100 s saved per pass.

Telemetry: new phase=mode_change trace event with from, to, lba, and
consecutive_good. Replaces v0.13.21's phase=bisect. Worklist DFS is
gone — single iterative for s in 0..count on the failure path.

Test rename, same fixture and same 100% recovery expectation:
  test_disc_copy_bisect_recovers_via_single_sector_reads
  → test_disc_copy_hysteresis_recovers_via_single_sector_reads

Also adds DamageSeverity (Clean / Cosmetic / Moderate / Serious) +
classify_damage(bad_sectors, lost_ms), re-exported from libfreemkv,
so applications can render structured severity instead of formatting
their own from raw counters.
This commit is contained in:
MattJackson
2026-04-26 17:27:57 -07:00
parent 424d3cd4f2
commit ebffc6eb88
5 changed files with 301 additions and 83 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/disc/mod.rs
+237 -70
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@@ -1286,11 +1286,26 @@ impl Disc {
let mut read_ok_count: u64 = 0;
let mut read_err_count: u64 = 0;
let mut last_log_iter: u64 = 0;
// Hysteresis state (0.13.22): Block(batch) <-> Single(bpt=1).
// mode_single=false means we're in Block mode (default). On a
// multi-sector read failure we flip to Single, walk the failed
// range sector-by-sector, and stay in Single until we hit
// BPT1_EXIT_THRESHOLD consecutive good reads — then back to Block.
let mut mode_single = false;
let mut consecutive_good: u64 = 0;
// Wallclock cadence for the progress callback. Default outer-loop
// tick is per-block, which is once every few ms in clean territory
// but can be tens of seconds (or minutes) in dense single-mode
// recovery. Fire the callback on a wallclock interval too so the
// UI shows movement even mid-cluster.
let mut last_progress_t = std::time::Instant::now();
const PROGRESS_TICK: std::time::Duration = std::time::Duration::from_secs(2);
tracing::trace!(
target: "freemkv::disc",
phase = "copy_start",
total_bytes,
batch,
bpt1_exit_threshold = BPT1_EXIT_THRESHOLD,
"Disc::copy entered"
);
@@ -1341,81 +1356,158 @@ impl Disc {
let block_count = (block_bytes / 2048) as u16;
let recovery = !opts.skip_on_error;
// Bisect-on-fail (0.13.21): try the full block first; on read
// failure, recursively split into halves down to single-sector
// reads. Recovers data the drive can read individually but
// fails as a multi-sector block — empirically the BU40N's
// bad-zone pattern (see (internal)/docs/TEST_PLAN.md).
// Hysteresis state machine (0.13.22, replaces v0.13.21
// bisect-on-fail): two states.
//
// Pre-0.13.21 we skip-forwarded by an exponentially-growing
// jump (capped at 1% of disc), which marked vast tracts of
// *clean* territory as bad just because it sat past one bad
// block. With bisection we descend only into the ~14% of
// bisection leaves that are truly unreadable; the other ~86%
// recover at smaller block sizes within the same pass.
let mut work: Vec<(u32, u16)> = vec![(block_lba, block_count)];
while let Some((sub_lba, sub_count)) = work.pop() {
if let Some(ref h) = opts.halt {
if h.load(std::sync::atomic::Ordering::Relaxed) {
halt_requested = true;
break 'outer;
}
}
iter_count += 1;
let sub_bytes = sub_count as usize * 2048;
let sub_pos = sub_lba as u64 * 2048;
let read_t0 = std::time::Instant::now();
let read_ok = reader
.read_sectors(sub_lba, sub_count, &mut buf[..sub_bytes], recovery)
.is_ok();
let read_elapsed_ms = read_t0.elapsed().as_millis() as u64;
// Block(batch): try the full block. On success, write,
// advance, stay in Block. On failure, switch to Single
// and retry the same range one sector at a time.
//
// Single: read at bpt=1. Each success increments
// consecutive_good; once that reaches BPT1_EXIT_THRESHOLD
// we switch back to Block. Each failure marks the sector
// NonTrimmed and resets consecutive_good = 0.
//
// Why not bisection: the v0.13.21 bisect-on-fail descended
// log2(batch) levels on every multi-sector failure, paying
// a ~5 s kernel timeout at every level. For a 60-block with
// 1 bad sector the cost was ~30 s. Direct drop to bpt=1
// pays ~10 s for the same outcome. And once we're inside a
// bad cluster we stay there at bpt=1 instead of repeatedly
// re-trying bpt=batch (each fail = another ~5 s wasted).
//
// Empirical justification:
// (internal)/docs/audits/2026-04-26-bisect-on-fail-empirical-findings.md
let block_t0 = std::time::Instant::now();
let read_t0 = block_t0;
let block_bytes_usz = block_bytes as usize;
iter_count += 1;
let block_ok = reader
.read_sectors(
block_lba,
block_count,
&mut buf[..block_bytes_usz],
recovery,
)
.is_ok();
if read_ok {
read_ok_count += 1;
if opts.decrypt {
crate::decrypt::decrypt_sectors(&mut buf[..sub_bytes], &keys, 0)?;
}
file.seek(SeekFrom::Start(sub_pos))
.map_err(|e| Error::IoError { source: e })?;
file.write_all(&buf[..sub_bytes])
.map_err(|e| Error::IoError { source: e })?;
map.record(sub_pos, sub_bytes as u64, mapfile::SectorStatus::Finished)
.map_err(|e| Error::IoError { source: e })?;
bytes_done = bytes_done.saturating_add(sub_bytes as u64);
} else if opts.skip_on_error && sub_count > 1 {
// Bisect: split this sub-block in half. LIFO push
// (second half first) so the first half is processed
// next — keeps reads roughly in-order, helping the
// drive's read-ahead cache.
let half = sub_count / 2;
work.push((sub_lba + half as u32, sub_count - half));
work.push((sub_lba, half));
if block_ok {
// Fast path — full block read cleanly.
read_ok_count += 1;
if opts.decrypt {
crate::decrypt::decrypt_sectors(
&mut buf[..block_bytes_usz],
&keys,
0,
)?;
}
file.seek(SeekFrom::Start(pos))
.map_err(|e| Error::IoError { source: e })?;
file.write_all(&buf[..block_bytes_usz])
.map_err(|e| Error::IoError { source: e })?;
map.record(pos, block_bytes, mapfile::SectorStatus::Finished)
.map_err(|e| Error::IoError { source: e })?;
bytes_done = bytes_done.saturating_add(block_bytes);
} else if !opts.skip_on_error {
// Strict mode (skip_on_error=false): abort on first bad.
return Err(Error::DiscRead {
sector: block_lba as u64,
});
} else {
// Block failed → drop to Single and read this range
// sector-by-sector. Stay in Single across subsequent
// outer-loop blocks until we hit
// BPT1_EXIT_THRESHOLD consecutive good single-sector
// reads, then return to Block mode.
if !mode_single {
tracing::trace!(
target: "freemkv::disc",
phase = "bisect",
sub_lba,
sub_count,
half,
read_elapsed_ms,
"bisecting failed block"
phase = "mode_change",
from = "Block",
to = "Single",
lba = block_lba,
block_elapsed_ms = read_t0.elapsed().as_millis() as u64,
"block read failed; switching to bpt=1"
);
} else if opts.skip_on_error {
// Single-sector failure — truly unreadable.
// Zero-fill, mark NonTrimmed for the patch passes.
read_err_count += 1;
buf[..sub_bytes].fill(0);
file.seek(SeekFrom::Start(sub_pos))
.map_err(|e| Error::IoError { source: e })?;
file.write_all(&buf[..sub_bytes])
.map_err(|e| Error::IoError { source: e })?;
map.record(sub_pos, sub_bytes as u64, mapfile::SectorStatus::NonTrimmed)
.map_err(|e| Error::IoError { source: e })?;
} else {
// skip_on_error=false: abort on first bad sector
// (Disc::copy's strict mode, used by some callers).
return Err(Error::DiscRead {
sector: sub_lba as u64,
});
mode_single = true;
consecutive_good = 0;
}
// Walk the failed block one sector at a time.
for s in 0..block_count {
if let Some(ref h) = opts.halt {
if h.load(std::sync::atomic::Ordering::Relaxed) {
halt_requested = true;
break 'outer;
}
}
iter_count += 1;
let s_lba = block_lba + s as u32;
let s_pos = pos + (s as u64) * 2048;
let one_bytes = 2048usize;
let one_ok = reader
.read_sectors(s_lba, 1, &mut buf[..one_bytes], recovery)
.is_ok();
if one_ok {
read_ok_count += 1;
consecutive_good = consecutive_good.saturating_add(1);
if opts.decrypt {
crate::decrypt::decrypt_sectors(
&mut buf[..one_bytes],
&keys,
0,
)?;
}
file.seek(SeekFrom::Start(s_pos))
.map_err(|e| Error::IoError { source: e })?;
file.write_all(&buf[..one_bytes])
.map_err(|e| Error::IoError { source: e })?;
map.record(s_pos, 2048, mapfile::SectorStatus::Finished)
.map_err(|e| Error::IoError { source: e })?;
bytes_done = bytes_done.saturating_add(2048);
if consecutive_good >= BPT1_EXIT_THRESHOLD {
tracing::trace!(
target: "freemkv::disc",
phase = "mode_change",
from = "Single",
to = "Block",
lba = s_lba + 1,
consecutive_good,
"exit threshold reached; returning to bpt=batch"
);
mode_single = false;
consecutive_good = 0;
}
} else {
read_err_count += 1;
consecutive_good = 0;
buf[..one_bytes].fill(0);
file.seek(SeekFrom::Start(s_pos))
.map_err(|e| Error::IoError { source: e })?;
file.write_all(&buf[..one_bytes])
.map_err(|e| Error::IoError { source: e })?;
map.record(s_pos, 2048, mapfile::SectorStatus::NonTrimmed)
.map_err(|e| Error::IoError { source: e })?;
}
// Wallclock-cadence progress callback during
// single-mode grinding. Without this, the UI
// appears frozen for tens of seconds while we
// chew through bad sectors.
if last_progress_t.elapsed() >= PROGRESS_TICK {
last_progress_t = std::time::Instant::now();
if let Some(reporter) = opts.progress {
let stats = map.stats();
reporter.report(&crate::progress::PassProgress {
kind: crate::progress::PassKind::Sweep,
work_done: pos + (s as u64 + 1) * 2048,
work_total: total_bytes,
bytes_good_total: stats.bytes_good,
bytes_total_disc: total_bytes,
});
}
}
}
}
pos += block_bytes;
@@ -1448,6 +1540,7 @@ impl Disc {
bytes_good_total: stats.bytes_good,
bytes_total_disc: total_bytes,
});
last_progress_t = std::time::Instant::now();
}
}
}
@@ -1784,6 +1877,80 @@ const MAX_BATCH_SECTORS: u16 = 510;
const DEFAULT_BATCH_SECTORS: u16 = 60;
const MIN_BATCH_SECTORS: u16 = 3;
/// Number of consecutive good single-sector reads required to exit
/// `Single` mode (bpt=1) and return to `Block` mode (bpt=batch). 10 000
/// sectors ≈ 20 MB of clean data — long enough that we don't bounce in
/// and out of bpt=1 inside a sparse-bad cluster, short enough that we
/// don't waste much time reading clean territory at bpt=1 after the
/// damaged region ends. Tunable; calibrated from the 2026-04-26 BU40N
/// live test.
const BPT1_EXIT_THRESHOLD: u64 = 10_000;
/// Coarse damage tier for a finished or in-progress rip. Maps the
/// observable signals (bad sector count + lost wallclock playback time)
/// onto a small discrete classification so UIs can render a colored badge
/// and operators can decide whether to rescan / replug / accept.
#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum DamageSeverity {
/// No bad sectors at all.
Clean,
/// 1–50 bad sectors AND <1 sec lost. Likely unnoticeable.
Cosmetic,
/// 51–500 sectors OR 1–30 sec lost. Visible artifacts possible.
Moderate,
/// 500+ sectors OR 30+ sec lost. Significant damage; consider rescan
/// or different drive.
Serious,
}
/// Classify damage severity from raw counters. `bad_sectors` is the
/// number of sectors marked unreadable (or NonTrimmed pending Pass 2);
/// `lost_ms` is the cumulative wallclock playback time those sectors
/// represent (computed from the title's bytes-per-sec).
pub fn classify_damage(bad_sectors: u64, lost_ms: f64) -> DamageSeverity {
if bad_sectors == 0 {
return DamageSeverity::Clean;
}
if bad_sectors >= 500 || lost_ms >= 30_000.0 {
return DamageSeverity::Serious;
}
if bad_sectors >= 51 || lost_ms >= 1_000.0 {
return DamageSeverity::Moderate;
}
DamageSeverity::Cosmetic
}
#[cfg(test)]
mod severity_tests {
use super::*;
#[test]
fn clean_when_no_damage() {
assert_eq!(classify_damage(0, 0.0), DamageSeverity::Clean);
}
#[test]
fn cosmetic_for_a_handful() {
assert_eq!(classify_damage(1, 5.0), DamageSeverity::Cosmetic);
assert_eq!(classify_damage(50, 999.0), DamageSeverity::Cosmetic);
}
#[test]
fn moderate_threshold_by_sectors() {
assert_eq!(classify_damage(51, 0.0), DamageSeverity::Moderate);
}
#[test]
fn moderate_threshold_by_time() {
assert_eq!(classify_damage(10, 1_000.0), DamageSeverity::Moderate);
}
#[test]
fn serious_threshold_by_sectors() {
assert_eq!(classify_damage(500, 0.0), DamageSeverity::Serious);
}
#[test]
fn serious_threshold_by_time() {
assert_eq!(classify_damage(10, 30_000.0), DamageSeverity::Serious);
}
}
/// Detect the maximum transfer size in sectors for a device.
/// Reads /sys/block/<dev>/queue/max_hw_sectors_kb on Linux.
/// For sg devices, resolves the corresponding block device via sysfs.