SashegDev
874b6f20c2
Основа — Horizon (MIT). История апстрима не переносится: этот репозиторий ведёт свою.
91 lines
4.8 KiB
Markdown
91 lines
4.8 KiB
Markdown
# Block entity save batches
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`Game::with_entities` prepares each dimension-change, full-save and dirty-unload
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batch through `save::chunks_with_block_entities`. For multiple chunks, it visits
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the live block-entity and custom-name maps once, groups borrowed entries only for
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requested coordinates, then clones their contents one chunk at a time. The
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single-chunk path keeps the original filters; an empty batch visits neither map.
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Chunk input order, map iteration order within each chunk, duplicate inputs and
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arithmetic `>> 4` mapping for negative coordinates are preserved. World maps and
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original `Arc<Chunk>` values remain untouched. Attaching tick/extras data, draining
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modified flags, unload cleanup, synchronous save errors and asynchronous save
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queue errors retain their existing order and handling.
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## Reproduce
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From this worktree, with no other benchmark running:
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```sh
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export CARGO_INCREMENTAL=0
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export CARGO_TARGET_DIR=/home/bob/Documents/horizon/target
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cargo build --profile fast -p horizon-client --example save_batch_bench
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taskset -c 2 "$CARGO_TARGET_DIR/fast/examples/save_batch_bench"
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cargo test --profile fast -p horizon-client --lib save::tests
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cargo clippy --profile fast -p horizon-client --all-targets -- -D warnings
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cargo fmt --all -- --check
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```
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Change the target directory and CPU affinity for other machines. The example
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constructs all fixtures itself and removes its temporary biome/colormap inputs.
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It compares a copy of the previous per-chunk scans against the actual production
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helper on the same maps and chunks, validates exact full chunk NBT bytes (not
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just entity counts), warms both paths five times, and reports medians of 21
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alternating samples. Each sample repeats enough batches for approximately 10 ms
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of the slower path, capped at 10,000 repetitions; large batches run once.
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Inputs and outputs pass through `black_box`. Destruction of outputs is timed.
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## Scope and memory
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The fixtures cover a 16 by 16 loaded area spanning negative and positive chunks:
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3,072 block entities / 768 names for a village and 12,288 / 3,072 for storage.
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Each chunk has 12 or 48 mixed chests, furnaces and signs, with populated
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inventories, custom item components, names, saved NBT overlays, saved entity
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order, and an unmodelled end gateway. Batch sizes are 0, 1, 16, 64 and 256 chunks.
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Terrain uses eight uniform stone sections plus sections containing the entities;
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the minimal registry has five states and one biome. Prepared production assets
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were not found in the relevant project/Horizon cache/data locations, so these
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are synthetic workloads rather than captured saves.
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`snapshot` measures the production grouping/clone helper. `snapshot+nbt` also
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is optional (`--nbt`) and calls the production `save::encode` and
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`nbt::write_named` paths, with no
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precomputed save tables. Both exclude `Game::attach_save_data`, writer queueing,
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compression, region I/O, rendering and startup. They do not establish an overall
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save-latency, startup or FPS improvement. Serialization and populated inventory
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clones can dominate this CPU stage.
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The multi-chunk path adds an O(chunk-count) index and O(selected-entity +
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selected-name) borrowed pairs (16 bytes per pair on this 64-bit machine, plus
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vector spare capacity). It also temporarily stores input chunk references and
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cloned `Chunk` values before the game wraps them in `Arc`. Unsaved entity/name
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contents are not cloned, and the owned snapshots remain independent of unload
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cleanup. No full-world cache or persistent index is added.
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## Recorded results
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Recorded on 2026-10-15: AMD Ryzen 5 5600X, Linux 7.2.8-zen1-2-zen,
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`rustc 1.99.0 (b940084d7 2026-09-28)`, `fast` profile (optimized, LTO off,
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16 codegen units), `CARGO_INCREMENTAL=0`, pinned to logical CPU 2. The retained
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run followed completion of other Rust builds; a contended trial was discarded.
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Full raw medians, repetitions, entity counts and NBT byte counts are in
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[save-batch-entities.csv](save-batch-entities.csv).
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| Fixture | Saved chunks | Before (ms) | After (ms) | Speedup |
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| --- | ---: | ---: | ---: | ---: |
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| village | 1 | 0.043732 | 0.043813 | 0.998x |
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| village | 16 | 0.695763 | 0.578064 | 1.204x |
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| village | 64 | 8.185510 | 7.467929 | 1.096x |
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| village | 256 | 38.434320 | 36.447195 | 1.055x |
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| storage | 1 | 0.172842 | 0.170303 | 1.015x |
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| storage | 16 | 3.688055 | 3.242919 | 1.137x |
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| storage | 64 | 35.799641 | 33.446834 | 1.070x |
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| storage | 256 | 155.262657 | 147.501719 | 1.053x |
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Multi-chunk snapshot speedups were 1.053–1.204x (5.0–16.9% less time).
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Single-chunk village time changed by +0.19%, and storage by -1.47%; the original
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scan strategy remains in place for both. Empty batches skip the maps, and their
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nanosecond-scale ratios in the CSV should not be treated as a throughput claim.
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All ten cases passed exact NBT byte equality, including names and block entities.
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Optional combined serialization timings were not retained in this result set.
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