@nedbatNed Batchelder wow. Trying it on a very small pure Python lib (inifix), branch coverage on:
coverage 7.6.11 (default): ~3s
coverage 7.6.11 (COVERAGE_CORE=sysmon): ~1.5s
coverage 7.7.0 (COVERAGE_CORE=sysmon): ~<1.0s
without coverage, the test suite runs in about 800ms, so the overhead needed to measure coverage went from ~275% to a measly 25%.
@neutrinocerosClément Robert 
@nedbatNed Batchelder
Testing 
@pillow
Without branch coverage (and without sysmon), it's about 80 seconds for both 7.6.12 and 7.7.0.
Without branch coverage (and using sysmon), it's about 38 seconds for both 7.6 and 7.7.
With branch coverage (and using sysmon), coverage 7.7 ran 2.42 times faster than 7.6!
107 -> 44 seconds!
![Benchmark output of both versions.
❯ hyperfine \
--prepare "python3.14 -m pip install 'coverage<7.7'" \
"COVERAGE_CORE=sysmon python3.14 -m pytest --cov PIL --cov Tests" \
--command-name coverage-7.6 \
--prepare "python3.14 -m pip install 'coverage>=7.7'" \
"COVERAGE_CORE=sysmon python3.14 -m pytest --cov PIL --cov Tests" \
--command-name coverage-7.7 \
--runs 2
Benchmark 1: coverage-7.6
Time (mean ± σ): 107.346 s ± 0.398 s [User: 94.429 s, System: 10.319 s]
Range (min … max): 107.064 s … 107.627 s 2 runs
Benchmark 2: coverage-7.7
Time (mean ± σ): 44.281 s ± 0.547 s [User: 32.046 s, System: 10.382 s]
Range (min … max): 43.894 s … 44.668 s 2 runs
Summary
coverage-7.7 ran
2.42 ± 0.03 times faster than coverage-7.6
❯ python3.14 --version
Python 3.14.0a6](https://files.mastodon.social/media_attachments/files/114/184/030/105/487/139/original/38e0dc420025b1c2.png)
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