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#149: measure the filed suspect -- the #141 segment sweep is EXONERATED; ship [segperf] telemetry

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A/B on identical 2-node beam-heavy runs (scratchpad/night14/segperf.sh),
BT_BEAM_SEGFRESH=1 (swept behaviour) vs =0 (pre-sweep compose at the beam
site, the only per-frame swept call):

                    fresh(swept)   legacy(pre-sweep)
  rstat blocks>50ms       0              0
  maxDraw worst         730ms          646ms      (mission-load spike, BOTH)
  segperf dirty-passes   38/s            4/s      <- the sweep DOES multiply
  segperf accessor ms   0.97/s          0.57/s    <- ...by 0.4 ms/s.  Noise.

So the invalidation-storm hypothesis I filed on #149 is wrong by three orders
of magnitude, and Oracle's sustained 50-104ms stall window does NOT reproduce
on this rig at all.  Refusing to guess a third time: the build now carries the
telemetry to answer it on the machine that actually regresses --

  [segperf] calls= dirty= ms=   printed beside every [rstat] window under
  BT_PERF_LOG (JMOVER counters; two integer increments when unset), and
  BT_BEAM_SEGFRESH=0 remains as a one-env A/B for the beam site.

Default stays FRESH (the swept accessor): its measured cost is trivial and it
is the correctness-cautious side while the peer-beam-staleness question is
unmeasured.

Next for #149: Oracle runs one session with BT_PERF_LOG=1.  If [segperf] ms is
large inside his stalled windows, segment work is implicated on HIS
configuration and BT_BEAM_SEGFRESH=0 gives the immediate A/B; if it is small
(as here), the stall is elsewhere in the 817->857 delta and we hunt with his
numbers instead of my theories.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018SgmXGNMXavXiafKXf9MDC
This commit is contained in:
Joe DiPrima
2026-08-09 16:46:10 -05:00
co-authored by Claude Opus 5
parent 84f8b1c415
commit a77c5a1407
4 changed files with 122 additions and 1 deletions
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game/reconstructed/mech4.cpp
+13 -1
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@@ -9031,8 +9031,20 @@ void
// This is the BEAM muzzle -- the same stale-cache exposure the
// missile launch had, so a peer's beam would also originate
// from the bind-pose gun port instead of the twisted torso.
// #149 A/B (BT_BEAM_SEGFRESH=0): revert THIS site to the
// pre-sweep plain compose, to measure whether the per-beam
// per-frame dirty-pass is the 857 draw-stall regression.
// This site runs inside the DRAW path per emitter per frame;
// the other swept sites are per-salvo/per-hit and cannot be
// a per-frame cost. Default = fresh (the swept behaviour).
static const int sBeamFresh =
!(getenv("BT_BEAM_SEGFRESH") && *getenv("BT_BEAM_SEGFRESH") == '0');
LinearMatrix mw;
GetSegmentToWorld(*s_portCache[energyOrdinal], &mw);
if (sBeamFresh)
GetSegmentToWorld(*s_portCache[energyOrdinal], &mw);
else
mw.Multiply(s_portCache[energyOrdinal]->GetSegmentToEntity(),
localToWorld);
mz = mw; // Point3D = matrix translation
}
}