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MP: peer shakiness ROOT-CAUSED as single-box packet jitter (rig, not game) + affinity launcher (task #50)

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The residual RANDOM peer shakiness on accel/decel was proven (BT_RXJIT record
inter-arrival probe) to be TEST-RIG packet jitter, not the game: two Debug btl4
nodes on one box contend for CPU, so Windows batches their TCP delivery -- records
arrive in bursts (max 56-226ms gaps, burstiness 3-7x) instead of even ~17ms.  The
peer dead-reckons across the gaps then snaps -> random shake.  Pinning the nodes to
disjoint cores restored even ~17ms delivery (burstiness ~1.0) and the shakiness
vanished (user-confirmed 'that was it').  Real pods = dedicated machines, no
contention -> never see it.  So NO un-authentic jitter buffer -- the coupled
body-channel peer (96a896a/f094d78/23f1532) is the authentic + correct finish.

 - mech.cpp: BT_RXJIT record-arrival-jitter probe (env-gated).
 - tools/mp_launch.sh: 2-node launcher that pins nodes to disjoint cores (bakes in
   the fair-delivery condition; documents why).
 - context/multiplayer.md: the finding, so it is not re-litigated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
arcattack
2026-07-15 08:14:22 -05:00
co-authored by Claude Opus 4.8
parent 23f1532fb0
commit 49d73dc8e2
3 changed files with 69 additions and 0 deletions
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game/reconstructed/mech.cpp
+27
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@@ -1790,6 +1790,33 @@ Logical
void
Mech::ReadUpdateRecord(Simulation::UpdateRecord *message)
{
// RECORD-CADENCE probe (BT_RXJIT): quantify how EVENLY records arrive (wall-clock
// ms between arrivals) -- the jitter that makes the peer's corrections random.
if (getenv("BT_RXJIT") && GetInstance() == ReplicantInstance)
{
LARGE_INTEGER _now, _freq;
QueryPerformanceCounter(&_now); QueryPerformanceFrequency(&_freq);
static double s_lastMs = 0.0, s_min = 1e9, s_max = 0.0, s_acc = 0.0;
static int s_n = 0, s_rep = 0;
const double nowMs = (double)_now.QuadPart * 1000.0 / (double)_freq.QuadPart;
if (s_lastMs > 0.0)
{
const double gap = nowMs - s_lastMs;
s_n++; s_acc += gap;
if (gap > s_max) s_max = gap;
if (gap < s_min) s_min = gap;
}
s_lastMs = nowMs;
if (++s_rep >= 120 && s_n > 0)
{
DEBUG_STREAM << "[rxjit] records/win=" << s_n
<< " gapMs min=" << s_min << " avg=" << (s_acc / s_n)
<< " max=" << s_max
<< " burstiness(max/avg)=" << (s_max / (s_acc / s_n))
<< "\n" << std::flush;
s_rep = 0; s_n = 0; s_acc = 0.0; s_min = 1e9; s_max = 0.0;
}
}
static const int s_mrecLog = getenv("BT_REPL_LOG") ? 1 : 0;
if (s_mrecLog && message->recordID != 0)
DEBUG_STREAM << "[mrec-rx] type=" << (int)message->recordID