Each frame the game waits in one nvnSyncWait (1.2.1 lr 0x7000b23dfc) for the frame it presented last. On the Switch
that work is long done by then; here it is still in the replay and on the GPU, and on Great Sky Island the wait is
about 4.6 ms of a 13 ms frame. With TOTK_SYNC_AHEAD=1 that one wait waits for the frame before it instead, once the
replay thread submitted the asked value, so the game builds the next frame while the GPU runs the last one.
The game then writes guest memory that GPU work still in flight reads. Shadow storage makes that safe: a shadow update
of a pool with a reader in flight is queued and copied by the GPU in the next part's prologue, in queue order, instead
of memcpy'd under that reader (TOTK_SHADOW_DEFER=1, the default with the switch; 0 makes the replay thread wait for
the reader instead). The guard is read under the shadow lock and the wait takes that lock once after raising it, so no
sync that read the old guard is still copying when the game writes again. The switch needs shadow storage (Linux and
Wine by default, TOTK_SHADOW=1 on native Windows) and the 1.2.1 call site; otherwise it stays off with a log line.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
On Linux, write-protecting memory the GPU imported costs milliseconds per submit and the import's pinning clears the
write watch, so each CPU-visible pool gets a host-visible copy instead: the pages the CPU wrote since the last sync go in
right before each submit (skipping bytes the GPU still has to write back), and the replay's GPU writes are copied back
into guest memory at their fence (vk_gpu_written). In 1.2.1 play it costs about 0.2 ms a frame. TOTK_SHADOW=1 turns it
on under Windows too.
Also: build_game.py fetches the VMA header the Windows release pins when the system has none; plat_localtime and
plat_gmtime reject the times Windows rejects; the SDL text entry honours TOTK_SWKBD_TEST=cancel; probe-vkmem follows
the replay's protocol for GPU writes and syncs.
Shared runtime code now goes through runtime/platform/platform.h, implemented by platform/win32.c and a new
platform/linux.c: futex locks, a userfaultfd and PAGEMAP_SCAN write watch, signal-based async preemption, our own
fiber switch, and a SIGSEGV handler for the thaw and crash hooks. The window, input, menu and software keyboard get
SDL3 back ends beside the Win32 ones, with the swapchain (gfx_present.c) and input merging (input.c) shared. SHA-256
replaces BCrypt, ELF builds get their own override sections, and the build tools gain Linux branches.
On Linux the selftest and the gfx-abi, astc, nvn and window probes pass. probe-vkmem still fails: imported guest
memory cannot be write-watched on Linux, which the shadow buffers in vk_memory.c will address.
Comments cited codes from local notes (port-lessons P1, backlog), task labels (T6c1-T6c3, M4), bare upstream commit
hashes and issue numbers, a file that no longer exists (nvn_api.c, now nvn_api_*.c), a generated file (main_0103.c)
and line numbers into upstream files that refs/ has moved past, so they pointed at unrelated code. Those now name the
file, function or project and say what the cited code does. Attribution of copied code keeps its pinned commits.
Corrected facts: TOTK_REPLAY_ASYNC defaults to 0, and the shader cache, pipeline cache and pipeline keys live next to
totk.exe, not in build/v121.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Comments named the agent task (T1-T7, M2-M5, Task 2.x) that once owned each file or block, and pointed at local
notes the repository does not carry (backlog items, milestone plans, research notes). They now say what the code
does. gfx_stubs.c held weak stand-ins for functions that every build has defined for a long time.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A guest WriteTexels of a small region deswizzled and reswizzled the whole level while its thread held a virtual core
and the texture lock: 80 ms preemption delays and 50-160 ms frames in the monsters2 replay (frames 765-790,
1225-1235), with the render thread waiting on the texture lock. nvn_texels_box copies the box alone; probe-vkmem
compares it with the whole-level path on random boxes of five block sizes, mip levels, array layers and 3D slices.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
