Metrics

The OpenROAD-flow-scripts repository contains source files (e.g., LEF/DEF, Verilog, SDC, Liberty, RC extraction) and configuration files (e.g. config.mk) that enable the user to run a small set of example designs through our complete RTL-to-GDS flow.

To keep track of the quality of the results, each design directory holds a rules file that gates the flow:

flow/designs/<platform>/<design>/rules-base.json

The file name comes from RULES_JSON, defined in flow/util/utils.mk:

export RULES_JSON ?= $(DESIGN_DIR)/rules-$(FLOW_VARIANT).json

FLOW_VARIANT defaults to base, which is why the committed file is rules-base.json. A run with a non-default FLOW_VARIANT looks for rules-<variant>.json, or you can point RULES_JSON at any file explicitly.

Each entry in the rules file is a metric name, a reference value, and a comparison operator. For example:

{
    "synth__design__instance__area__stdcell": {
        "value": 43.1,
        "compare": "<="
    },
    "detailedplace__design__violations": {
        "value": 0,
        "compare": "=="
    }
}

An entry may also carry "level": "warning", which reports a mismatch without failing the build.

The values a run is measured against are collected by flow/util/genMetrics.py into $(REPORTS_DIR)/metadata.json (reports/<platform>/<design>/<variant>/metadata.json). That file is generated output — it is not committed. flow/util/checkMetadata.py compares it against the rules file.

Checking against the rules

The evaluation checks key metrics (e.g., worst slack, number of DRCs) to ensure that changes do not degrade the results.

After you make a significant change — e.g., fixing a bug in a piece of code, or changing a configuration variable such as PLACE_DENSITY — review the results and compare them against the rules. To perform the check, run:

cd OpenROAD-flow-scripts/flow
# clean_metadata is only required if you need to re-run the check
make [clean_metadata] metadata

make metadata runs three steps in order: finish (the full flow), metadata-generate (write metadata.json), and metadata-check (compare it against RULES_JSON). The check log is written to $(REPORTS_DIR)/metadata-check.log.

If you only changed synthesis, you can gate a synthesis-only run against the synthesis subset of the same rules file, without running the rest of the flow:

make metadata-synth

If the check reports any error, review it to make sure the change in metrics is expected and justifiable. If so, proceed to the next section to update the reference values.

Update process

Updating the rules file is mandatory if a metric became worse than the value allowed by rules-base.json (see the previous section on how to perform the check). It is also a good idea to update it when your change improves a metric, so that the improvement is not silently lost later.

To update the rules file for a design, from a tree that has just been measured (so metadata.json exists):

cd OpenROAD-flow-scripts/flow
make update_ok

update_ok is an alias for update_rules. It runs flow/util/genRuleFile.py with --failing --tighten, which:

relaxes rules the current run fails, using the measured value plus a margin, so that small run-to-run variation does not break the flow; and
tightens rules the current run passes by a wide margin, so improvements are locked in.

The new file is written to $(REPORTS_DIR)/rules.json and then copied over $(RULES_JSON) — that copy is the file you commit.

If you need to overwrite every rule from the current run rather than only the failing and improved ones, use:

make update_rules_force

This runs genRuleFile.py --update. Prefer make update_ok; use the forced variant only when the metric set itself changed.

Reference metadata (`metadata-<variant>-ok.json`)

There is a second, optional file per design:

# writes flow/designs/<platform>/<design>/metadata-base-ok.json
make update_metadata

This copies the current metadata.json next to the design as metadata-$(FLOW_VARIANT)-ok.json. It is not what gates the flow — nothing in make metadata reads it. It is consumed only by flow/util/genReportTable.py when building the golden-vs-current report table, and almost no design commits one. Update the rules file, not this one, unless you are specifically working on that report.

Metrics

Checking against the rules

Update process

Reference metadata (metadata-<variant>-ok.json)

Reference metadata (`metadata-<variant>-ok.json`)