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regression: document the Shadow lsquic tick-floor patch

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Add a README covering why quic needs the tick-floor patch under Shadow
(zero-delay tick re-arm livelocks a discrete-event simulator), how the
LSQUIC_TICK_FLOOR_US gate works, which lsquic version the patch targets,
and how the build guards against a silent stock compile. Point the
Dockerfile comment at it.
This commit is contained in:
radiken
2026-07-24 11:09:17 +01:00
parent d22ff931bd
commit 29f32f5a23
2 changed files with 28 additions and 3 deletions
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nim-test-node/regression/Dockerfile_amd64_shadow
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@@ -34,9 +34,8 @@ COPY . .
RUN nimble refresh
RUN nimble install -dy --verbose
# Floor lsquic's engine tick re-arms, switched at runtime by LSQUIC_TICK_FLOOR_US
# (unset/0 = stock). Shadow livelocks on lsquic's diff=0 "tick now" re-arm.
# Patch the package cache: `nimble c` re-resolves and reinstalls over pkgs2.
# Floor lsquic's engine tick re-arms so Shadow can advance simulated time.
# Gated by LSQUIC_TICK_FLOOR_US (unset/0 = stock). See README.md.
COPY lsquic-tick-floor.patch /tmp/lsquic-tick-floor.patch
RUN set -eu; \
patched=0; \
nim-test-node/regression/README.md
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@@ -0,0 +1,26 @@
# Regression test node
Node for nim-libp2p regression campaigns. `Dockerfile_amd64` builds the static
cluster binary; `Dockerfile_amd64_shadow` builds the dynamic one for Shadow
(its syscall interposer only hooks dynamically linked ELFs).
## The lsquic tick-floor patch (Shadow + quic only)
`lsquic-tick-floor.patch`, applied by `Dockerfile_amd64_shadow`, is the reason
quic runs under Shadow at all. lsquic re-arms its engine tick with a zero delay;
in a discrete-event simulator that self-rescheduling timer never lets simulated
time advance, so the run livelocks at one instant. mplex and yamux are fine.
The patch floors the re-arm interval, gated by `LSQUIC_TICK_FLOOR_US` (unset/0 =
stock, so the image is safe on the cluster too; campaigns use `10000`, 10 ms).
`es_clock_granularity` is a real lsquic setting, but the essential change floors
nim-lsquic's own chronos re-arm, which has no upstream knob; the durable fix is
exposing both upstream in nim-lsquic.
## Maintaining the patch
It targets lsquic 0.5.4's layout, pinned in `test_node.nimble`. `nimble c`
re-resolves deps before compiling, so the Dockerfile patches the package cache
(`~/.nimble/pkgcache`, what nimble copies from) rather than the installed copy.
The build asserts it patched something and greps the binary for
`LSQUIC_TICK_FLOOR_US`, so a stock build or a stale pin fails loudly.