* ci: hold a CodSpeed run to the machine main's baseline was measured on
CodSpeed compares a run against a base run and refuses to call the
comparison meaningful when the two ran on different machines: the runner
uploads a `SystemInfo` record beside the profile carrying the OS, the
architecture, the CPU's vendor id, brand and flags, the physical core
count and the installed memory, and a hosted pool hands out whatever
machine is free. A simulated measurement is fixed against how fast the
machine is, but not against what it makes the process execute -- glibc
selects `memcpy` and the string routines through IFUNC on CPU flags, a
new stable rustc emits different code, and these benchmarks run each
program under CPython through pyo3 as well as under RustPython, so the
runner's default interpreter is an input too.
`scripts/codspeed-environment.py` records those fields plus the rustc,
libc and CPython versions, and compares a run against a recording. The
benchmark job now restores the recording main last wrote, records over it
when the ref is main, and compares against it otherwise; the install,
build and measure steps carry `if: steps.environment.outputs.match !=
'false'`, so a run that drew a different machine finishes green having
uploaded nothing. A missing or unfetchable recording is read as "nothing
to disagree with" rather than as a mismatch.
Assisted-by: Claude
* ci: read an unreadable environment recording as not a match
A cache miss, an eviction or a cache-service outage leaves the reference file
absent, and the comparison then reported `match=true`: every guarded step ran
and the run uploaded a measurement without having identified the machine it was
taken on.
An absent recording now reports `match=false`, and says so as a `::warning`
rather than the `::notice` a mismatch emits, so a job that measures nothing
because it has nothing to compare against is distinguishable from one that
measures nothing because the machine differs.
Assisted-by: Claude
