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Two things land together: the plan and contract draft P6 needs before it starts, and the
working notes that until now existed on exactly one machine.
1. P6's plan and contract draft (neither started; not one line of code)
docs/Disaggregated/P6-SPAWN-PLAN.md the package plan
docs/Disaggregated/P6-CONTRACT-DRAFT.md the contract draft (moves to
MG_Remote/CONTRACT-P6.md when c6 lands)
The three findings that mattered, all written into the documents:
a. P6 is SMALLER than its roadmap cell suggests. The transport primitives are already in
the tree and already tested: SocketDoorbell including hangup detection and the two
lost-wakeup fences (Doorbell.cpp:211-360, four cases in FdPassingTest), SCM_RIGHTS fd
passing, ShmSegment::Adopt, and the SurfaceOp / WindowKind schema already defined in
protocol.fbs. inproc uses a real second shm mapping rather than an alias, and
SessionRings.h:22-28 says that was done so today is not the first time it runs. P6 is
assembly plus a control plane plus a process, not "write a socket transport".
b. The evidence for "P6 is only a transport swap" has EXPIRED. It was bought by P5c, whose
audit found 59 direct memory accesses in a tree that already looked clean. P5e changed
the tree again. So the first package, a6, is a read-only audit that writes no code, and
every contract row that depends on it is marked PENDING a6 rather than decided in
advance.
c. P6 does not get a game running on the phone. ANativeWindow* is meaningless in the child,
and protocol.fbs:186-196's own comment says Android transfers the window out of band -
that band is P12. P6 lands pbuffer / surfaceless / offscreen, which is what HeadlessGL,
the split-equivalent lane and trace replay need, and which is exactly what P6's own exit
gate measures. A real window reaching the server is a named refusal. This gets its own
section because "P6 is done" would otherwise read as "the game runs now".
The contract adds rule G: a role may not name a process-local handle. It extends P5c's
rule E (a role may not name the other role's memory) from memory to identity - EGLDisplay /
EGLSurface / EGLContext / ANativeWindow* / fd number / pid / mapped address either cross as
a token this contract defines or they do not cross, and a descriptor crosses only through
SCM_RIGHTS, where the kernel renumbers it.
What P5e left for P6 gets its own section. The latch semantics are already designed
(ARCHITECTURE.md:504) and are copied unchanged. What is new is that after run-ahead the
client no longer waits while the peer process can DIE: the client holds records that were
published and will never be applied, and Android's freezer suspends the child without
closing anything. So slow and dead must be distinguishable WITHOUT a timeout threshold.
That is P6's only new design; everything else is carriage. It shares a predicate with E1's
outstanding re-specification (ID-122), and the two should be designed together.
Two gates carried over from P5e's lessons: G2 requires integration-spawn's test-name set to
match integration-split's name for name, because a differing set means the lane is quietly
running less; and the arm-proof gate requires every entry to record the child pid and
transport=spawn in its OWN private log - ID-124 established that this kind of false green
really happens, and a spawn lane that actually ran monolith would pass every other gate.
S2's shape must be settled before it is written, and the document says why: E1 is the
cautionary case.
2. The working notes move into the repository (docs/Disaggregated/notes/, 415 .md files)
ROADMAP / CURRENT_STAGE_PROGRESS / MEASUREMENTS cite ruling numbers, audit line numbers and
the provenance of gate figures from ~/w7/notes/, a directory that exists on one machine and
is under no version control. A record cited hundreds of times that lives only locally is not
a record, so it moves in whole, with its directory structure intact.
Only .md moves. Scripts, run logs, census and gate result JSON, patches, APKs and nm dumps
stay where they are: they are evidence DATA rather than documents - large, regenerated per
run, and mostly carrying absolute paths and device serials that mean something only on the
machine that produced them. The mapping and this split are written in
docs/Disaggregated/notes/README.md.
Two exceptions are recorded there too: P6's BRIEF has been promoted to a first-class
document and keeps no copy under notes/, so the two cannot drift apart; and recovered/ holds
material salvaged from failed workflow runs, which may duplicate the like-named phase
directories and is kept because a few of those were the only complete version at the time.
CI's citation lint takes docs/Disaggregated/*.md only (non-recursive), and notes/ is
deliberately outside it: those notes' file:line citations were written against their own
code heads, and resolving them against today's HEAD would fail wholesale - which is not an
error, it is their correct state as a historical record. To check one, use the revision it
declares (--rev).
3. Inconsistencies fixed in passing
- README.md's status line still said P5e was in progress while the stage table already said
closed.
- CURRENT_STAGE_PROGRESS's next-step item 1 still listed the exit gate as pending, though
(a) and (b) were run in the previous commit; rewritten to closed plus the one item that
actually remains (E1).
- ROADMAP's P6 row still had the pre-phase plan in three of its cells; it now carries the
package order, the scope boundary and the two new gates.
Checked with check_doc_citations.py: 125 citations across docs/Disaggregated/*.md, 0 problems.
48 lines
2.5 KiB
Markdown
48 lines
2.5 KiB
Markdown
# CORRECTION to `PERF-PROFILE-7c6f6886.md` §5 — run-ahead removes much less of the fill than §4 implied
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§4 is right that an unbarriered verb skips the residual fill. It is wrong to treat
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`MGPipeValidateForVerb`'s whole 18.03% as fill. The call tree under it (inproc, client thread,
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percentages relative to that subtree) says otherwise:
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| share of the subtree | child | skipped under run-ahead? |
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|---|---|---|
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| 22.05% | `MGPipeTracker::Update` | **no** — the tracker walk runs regardless |
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| 20.48% | `MGPipeShaderBufferEmitter::EmitClass` | **no** — emitters PRODUCE records, which is the whole of what an unbarriered verb hands the server |
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| 19.76% | `MGPipeFillAccess::CopyField` | **yes** |
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| ~6.7% | the sampler / vertex-input / program / framebuffer emitters | **no** |
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| remainder | self, including the unconditional prologue | partly |
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`PipeFill.cpp:3226-3231` says this in words: "What still runs, unchanged, is the tracker walk and the
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emitters (steps 2 and 3): those PRODUCE RECORDS, which is the whole of what an unbarriered verb is
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allowed to hand the server." So only about a fifth of that 18.03% goes away, i.e. **3.6 – 4.5% of the
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client thread**, not 18%.
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## The corrected prediction
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| | now | predicted after run-ahead |
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|---|---|---|
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| client GL thread | 6.1 ms/frame | **~3.9 ms/frame** (the 31.8% wait, plus ~4% of fill) |
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| apply thread | 5.3 ms/frame | ~2.0 ms/frame |
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| bound by | client | client |
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| implied fps | ~164 | **~250** |
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| monolith, same session | 3.9 – 4.8 ms/frame | 208 – 256 fps |
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**The honest claim is PARITY, not past it.** The split arm should land level with monolith, with the
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apply thread holding roughly 2 ms of headroom.
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Going beyond parity is separate work, and §2 of the profile already names its targets: the emitters
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and the encode path, which is where the client's remaining ~3.9 ms lives. The wait is not one of them
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any more once run-ahead lands.
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§5 of the profile note is left in place rather than edited, so the error is visible: it
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double-counted the tracker walk and the emitters as removable and produced ~3.0 ms / ~330 fps. This
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file supersedes it.
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## Why this matters beyond the number
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The first estimate was built by subtracting whole inclusive percentages of a symbol whose name
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suggested it was all fill. That is the same class of error the previous phase recorded after
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attributing an idle poll's cost to backend lock contention: **a percentage next to a plausible name
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is not an attribution.** The call tree was three commands away and it changed the conclusion from
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"comfortably ahead" to "level". Take the tree.
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