nim-ffi/tests/perf

C++ e2e perf harness

Measures the full foreign round trip — C++ driver → generated perfbench.hpp wrapper (CBOR encode) → libperfbench C ABI → FFI thread → Nim handler → back to C++ — across payload shapes, call lanes and thread counts. The nim-ffi analog of nim-brokers' test/ffibench (bench_e2e_driver.cpp / perf_driver.cpp), using the same O(1) parity predicate so the tables compare directly.

Timing is a measurement, not a gate: the harness is not part of nimble test. It still exits non-zero on any correctness failure — every reply is verified against the driver-side predicate, and every fired event must be delivered.

Running

nimble perf_cpp_e2e

Builds tests/perf/benchlib/perfbench.nim as a shared library with -d:danger (matching the tests/bench methodology) for each mm in the NIM_FFI_MM matrix (empty = orc + refc), regenerates the C++ bindings, builds the driver Release via CMake, and runs it. The generated nim_ffi_lib.cmake template is deliberately not used to build the lib — it produces a debug orc build, which would make the numbers meaningless.

What is measured

Every handler computes the same O(1) parity predicate ((a + b + int64(x)) and 1) == 0, so setups differ purely in transport cost (encode / copy / decode / thread crossing), never in handler work:

Setup	Wire shape	Lane
scalar	2 × int64 + 1 × float64 in, bool out	sync + async
payload N B	seq[byte] of N in, bool out; predicate reads (first, last, len) only	sync + async
event	sync trigger fires one on_perf_ping event of N B	delivery-latency

• sync — blocking round trips; per-call latency sampled (p50/p99).
• async — *Async future turnaround with a bounded in-flight window per thread (NIM_FFI_PERF_ASYNC_WINDOW); throughput only.
• event — the listener computes delivery latency from a driver-side steady_clock stamp passed through the Nim provider verbatim, so the delta stays inside one clock domain.

Each table row is one thread count: median msg/s over NIM_FFI_PERF_ITERS runs, latency percentiles pooled across runs, plus a csv,perf_ffi,... line per row for diff-friendly capture.

Env knobs

Knob	Default	Meaning
NIM_FFI_MM	both	orc / refc — mm matrix for the Nim lib build
NIM_FFI_PERF_THREADS	1,2,4,8	driver thread counts swept
NIM_FFI_PERF_PER_THREAD	2000	round trips per thread per run
NIM_FFI_PERF_ITERS	3	runs per row, median reported
NIM_FFI_PERF_PAYLOAD_SIZES	64,512,4096,65536	payload family sizes (bytes)
NIM_FFI_PERF_EVENT_PAYLOAD	512	event payload size (bytes)
NIM_FFI_PERF_ASYNC_WINDOW	64	in-flight futures per thread, async lane