The benchmarks in tests/benchmarks compare two versions. The program here answers a different question: which commit made something faster or slower. history.cpp is one fixed benchmark that uses only API 3.12.0 already has. history.py compiles it against the single_include of every first-parent commit that changed json.hpp or json_view.hpp, runs all of them interleaved, and writes one CSV row per commit with its pull request. The timeline in the post How 3.13.0 got faster comes from it. It is not built by CMake or run by CI.
| name | what it does |
|---|---|
parse_twitter, parse_citm, parse_canada | json::parse() of a std::string (citm_catalog.json as distributed is indented by four spaces) |
parse_citm_compact | the same with a minified copy of citm_catalog.json |
parse_twitter_ifstream | json::parse() of an std::ifstream, opening the file included |
accept_twitter | json::accept() |
view_parse_* | json_document::parse(); only where the header has json_view.hpp |
dump_twitter, dump_citm, dump_canada, dump4_citm | dump() and dump(4) |
from_cbor_twitter, to_cbor_twitter | read and write CBOR |
copy_destroy_citm | copy a parsed document and destroy the copy |
equal_citm | copy a parsed document and compare it with == |
Each workload runs in batches of at least 20 ms; the program prints the median of 9 batches in microseconds per call.
mkdir -p ~/history/data cp <json_test_data>/nativejson-benchmark/{twitter,citm_catalog,canada}.json ~/history/data/ python3 history.py build --repo ../../.. --work ~/history # about 300 builds, a few minutes in parallel caffeinate -i python3 history.py run --work ~/history --rounds 4 # about 1 h 45 min on an M1 Max (about 4 s per binary and round) python3 history.py summarize --work ~/history > history.csv
--extra DIR adds one more header directory, such as an amalgamation of develop with open pull requests merged in. run waits whenever the 1-minute load average is 4 or more.
A single commit can move a workload by a few percent through code layout alone: the functions it did not touch move to other addresses. Read a change as a step only if it is larger than that and stays. To check one, time the two commits against each other with more rounds, or compare instruction counts.