update: add a Rust fast-path when updating from null (and clean)
This case is easy to detect and we have all we need to generate a valid
working copy and dirstate entirely in Rust, which speeds things up
considerably:
On my machine updating a repo of ~300k files goes from 10.00s down to 4.2s,
all while consuming 50% less system time, with all caches hot.
Something to note is that further improvements will probably happen
with the upcoming `InnerRevlog` series that does smarter
mmap hanlding, especially for filelogs.
Here are benchmark numbers on a machine with only 4 cores (and no SMT enabled)
```
### data-env-vars.name = heptapod-public-2024-03-25-ds2-pnm
# benchmark.name = hg.command.update
# bin-env-vars.hg.py-re2-module = default
# bin-env-vars.hg.changeset.node = <this change>
# benchmark.variants.atomic-update = no
# benchmark.variants.scenario = null-to-tip
# benchmark.variants.worker = default
default: 5.328762 ~~~~~
rust: 1.308654 (-75.44%, -4.02)
### data-env-vars.name = mercurial-devel-2024-03-22-ds2-pnm
# benchmark.name = hg.command.update
# bin-env-vars.hg.py-re2-module = default
# bin-env-vars.hg.changeset.node = <this change>
# benchmark.variants.atomic-update = no
# benchmark.variants.scenario = null-to-tip
# benchmark.variants.worker = default
default: 1.693271 ~~~~~
rust: 1.151053 (-32.02%, -0.54)
### data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm
# benchmark.name = hg.command.update
# bin-env-vars.hg.py-re2-module = default
# bin-env-vars.hg.changeset.node = <this change>
# benchmark.variants.atomic-update = no
# benchmark.variants.scenario = null-to-tip
# benchmark.variants.worker = default
default: 38.901613 ~~~~~
rust: 11.637880 (-70.08%, -27.26)
### data-env-vars.name = netbsd-xsrc-public-2024-09-19-ds2-pnm
# benchmark.name = hg.command.update
# bin-env-vars.hg.py-re2-module = default
# bin-env-vars.hg.changeset.node = <this change>
# benchmark.variants.atomic-update = no
# benchmark.variants.scenario = null-to-tip
# benchmark.variants.worker = default
default: 4.793727 ~~~~~
rust: 1.505905 (-68.59%, -3.29)
```
#require test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "`dirname "$TESTDIR"`"
look for python scripts that do not use /usr/bin/env
$ testrepohg files 'set:grep(r"^#!.*?python") and not grep(r"^#!/usr/bi{1}n/env python") - **/*.t'
[1]
In tests, enforce $PYTHON and *not* /usr/bin/env python or similar:
$ testrepohg files 'set:grep(r"#!.*?python") and **/*.t' \
> -X tests/test-check-execute.t \
> -X tests/test-check-format.t \
> -X tests/test-check-module-imports.t \
> -X tests/test-check-pyflakes.t \
> -X tests/test-check-shbang.t \
> -X tests/test-highlight.t
[1]
The above exclusions are because they're looking for files that
contain Python but don't end in .py - please avoid adding more.
look for shell scripts that do not use /bin/sh
$ testrepohg files 'set:grep(r"^#!.*/bi{1}n/sh") and not grep(r"^#!/bi{1}n/sh")'
[1]