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61 lines
2.8 KiB
Markdown
61 lines
2.8 KiB
Markdown
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# C++ e2e perf harness
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Measures the full foreign round trip — C++ driver → generated `perfbench.hpp`
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wrapper (CBOR encode) → `libperfbench` C ABI → FFI thread → Nim handler → back
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to C++ — across payload shapes, call lanes and thread counts. The nim-ffi
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analog of nim-brokers' `test/ffibench` (`bench_e2e_driver.cpp` /
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`perf_driver.cpp`), using the same O(1) parity predicate so the tables compare
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directly.
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Timing is a measurement, not a gate: the harness is not part of `nimble test`.
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It still exits non-zero on any correctness failure — every reply is verified
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against the driver-side predicate, and every fired event must be delivered.
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## Running
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```sh
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nimble perf_cpp_e2e
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```
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Builds `tests/perf/benchlib/perfbench.nim` as a shared library with
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`-d:danger` (matching the `tests/bench` methodology) for each mm in the
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`NIM_FFI_MM` matrix (empty = orc + refc), regenerates the C++ bindings, builds
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the driver Release via CMake, and runs it. The generated
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`nim_ffi_lib.cmake` template is deliberately **not** used to build the lib —
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it produces a debug orc build, which would make the numbers meaningless.
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## What is measured
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Every handler computes the same O(1) parity predicate
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`((a + b + int64(x)) and 1) == 0`, so setups differ purely in **transport**
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cost (encode / copy / decode / thread crossing), never in handler work:
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| Setup | Wire shape | Lane |
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| --- | --- | --- |
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| scalar | 2 × `int64` + 1 × `float64` in, `bool` out | sync + async |
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| payload N B | `seq[byte]` of N in, `bool` out; predicate reads (first, last, len) only | sync + async |
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| event | sync trigger fires one `on_perf_ping` event of N B | delivery-latency |
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- **sync** — blocking round trips; per-call latency sampled (p50/p99).
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- **async** — `*Async` future turnaround with a bounded in-flight window per
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thread (`NIM_FFI_PERF_ASYNC_WINDOW`); throughput only.
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- **event** — the listener computes delivery latency from a driver-side
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`steady_clock` stamp passed through the Nim provider verbatim, so the delta
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stays inside one clock domain.
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Each table row is one thread count: median msg/s over `NIM_FFI_PERF_ITERS`
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runs, latency percentiles pooled across runs, plus a `csv,perf_ffi,...` line
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per row for diff-friendly capture.
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## Env knobs
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| Knob | Default | Meaning |
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| --- | --- | --- |
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| `NIM_FFI_MM` | both | `orc` / `refc` — mm matrix for the Nim lib build |
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| `NIM_FFI_PERF_THREADS` | `1,2,4,8` | driver thread counts swept |
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| `NIM_FFI_PERF_PER_THREAD` | `2000` | round trips per thread per run |
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| `NIM_FFI_PERF_ITERS` | `3` | runs per row, median reported |
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| `NIM_FFI_PERF_PAYLOAD_SIZES` | `64,512,4096,65536` | payload family sizes (bytes) |
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| `NIM_FFI_PERF_EVENT_PAYLOAD` | `512` | event payload size (bytes) |
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| `NIM_FFI_PERF_ASYNC_WINDOW` | `64` | in-flight futures per thread, async lane |
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