52 lines
1.7 KiB
Markdown
52 lines
1.7 KiB
Markdown
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# Phase 66: PGO (FAST minimal, GCC+LTO) — Instructions
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## Goal
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Use GCC PGO **without changing the toolchain** (keep GCC + `-flto`) to reduce layout tax and improve inline/layout decisions for the FAST minimal benchmark binary.
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## Principles (Box Theory)
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- No “link-out” pruning for performance (layout tax risk).
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- A/B must remain fair: same compiler/linker/LTO; only PGO profile differs.
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- Fail-fast: profile collection failures abort.
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## Workflow (Makefile SSOT)
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### Full pipeline
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```sh
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make pgo-fast-full
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```
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This runs:
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1. `make pgo-fast-profile` — builds profile-gen binaries (FAST minimal)
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2. `make pgo-fast-collect` — collects `.gcda` by running deterministic workloads
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3. `make pgo-fast-build` — builds PGO-optimized binary and renames it to `bench_random_mixed_hakmem_minimal_pgo`
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4. Runs Mixed 10-run with `BENCH_BIN=./bench_random_mixed_hakmem_minimal_pgo`
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### Manual steps (debug)
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```sh
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make pgo-fast-profile
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make pgo-fast-collect
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make pgo-fast-build
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BENCH_BIN=./bench_random_mixed_hakmem_minimal_pgo scripts/run_mixed_10_cleanenv.sh
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```
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## Profile workloads (SSOT)
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- Config file: `scripts/box/pgo_fast_profile_config.sh`
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- Collector: `scripts/box/pgo_tiny_profile_box.sh`
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The collector enforces a per-workload timeout and verifies `.gcda` generation.
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Important:
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- PGO は **training workload と benchmark preset/ENV の一致**が生命線。
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- `scripts/box/pgo_fast_profile_config.sh` は `scripts/run_mixed_10_cleanenv.sh` 経由で profile を取る（mismatch を避ける）。
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## GO / NO-GO
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- GO: Mixed 10-run mean **+1.0%** or more vs `bench_random_mixed_hakmem_minimal`
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- NEUTRAL: ±1.0% → keep as research target (do not promote)
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- NO-GO: -1.0% or worse → investigate profile mismatch / layout tax / workload coverage
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