bench: improve stateful benchmark reproducibility #35124

pull l0rinc wants to merge 4 commits into bitcoin:master from l0rinc:l0rinc/reset-stateful-benchmarks changing 4 files +22 −13

l0rinc commented at 2:48 PM on April 20, 2026: contributor

Context

Found while reviewing #35018, which led to a few additional benchmark fixes.

Problem

The CHACHA20 and FSCHACHA20POLY1305 benchmarks reused a single cipher object across timed calls. That advanced the stream state across samples, so later samples no longer measured work from the same starting point. A few other benchmarks could benefit from the same iteration-stability treatment, but that is outside the scope of this PR.

While investigating this, it also became clear that MempoolCheckEphemeralSpends only populated vin[0] in its loop, and that WalletBalanceMine duplicated WalletBalanceClean. The same review also showed that nanobench setup() can be misused as though it runs once per timed call.

Fix

Rebuild the ChaCha ciphers in setup() and pair that setup with epochIterations(1) so each timed call starts from the same state. Add a nanobench assertion that setup() is only used with epochIterations(1). Also fix the ephemeral spend benchmark inputs and remove the duplicate wallet balance benchmark.

bench: drop duplicate balance benchmark

`WalletBalanceMine` duplicated `WalletBalanceClean` exactly.
Remove the duplicate registration so the balance benchmark list stays distinct.

95b1366d57

bench: fix ephemeral spend inputs

`MempoolCheckEphemeralSpends` wrote every prevout to `tx2.vin[0]` instead of `tx2.vin[i]`.
That left only one child input pointing at the parent transaction, while the remaining inputs kept default prevouts.

Write each prevout to `vin[i]` instead.
Add an assertion that the last child input spends the last parent output.

37296a3347

bench: assert `setup()` is paired with `epochIterations(1)`

`setup()` in nanobench runs once per epoch, not once per timed call.
If an epoch executes the benchmark body multiple times, `setup()` can silently leave later iterations with different preconditions.

Fail fast when `setup()` is combined with anything other than `epochIterations(1)`.

d6f82e6968

bench: reset ChaCha cipher state

`CHACHA20` and `FSCHACHA20POLY1305` kept one cipher object alive across timed calls.
That advanced the stream state across samples, and `FSChaCha20Poly1305` could cross a rekey boundary.

Rebuild the cipher in `setup()` for each timed call so each sample starts from the same state.

b333754597

DrahtBot added the label Tests on Apr 20, 2026
DrahtBot commented at 2:49 PM on April 20, 2026: contributor



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ACK achow101

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achow101 commented at 7:35 PM on April 20, 2026: member

ACK b33375459764a3cc716723d596164299dd8c6e22

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#35018 wallet, bench: Use Nanobench setup() for wallet benchmarks, and remove DuplicateMockDatabase

bench: improve stateful benchmark reproducibility #35124

Context

Problem

Fix

Reviews