Use new hints.mostly-unused
#1491
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Most users of the `rustix` crate will use a fraction of its API surface area. Nightly rustc provides an option `-Zhint-mostly-unused` to tell it to defer as much compilation as possible, which provides a substantial performance improvement if most of that compilation doesn't end up happening. Cargo plumbs this option through using the new `[hints]` table. This will cause users of the `rustix` crate to default to setting `hint-mostly-unused`. (Top-level crates can override this if they wish, using a new profile option.) Note that setting this hint does not increase the MSRV of the rustix crate, as old versions of Cargo will ignore it. New versions of Cargo will respect it automatically (and, until we stabilize it, Cargo will do nothing unless you pass `-Zprofile-hint-mostly-unused` to cargo). Some sample performance numbers: this takes `rustix` compilation time with `all-apis` enabled from 5.9s to 4.3s (a 27% improvement).
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The FreeBSD test failure looks entirely unrelated. |
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Cool! Could you also add a comment, like "most users use a fraction of our API surface area, so this reduces compile times"? |
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@sunfishcode Done. |
sunfishcode
pushed a commit
that referenced
this pull request
Jul 15, 2025
* Use new `hints.mostly-unused` Most users of the `rustix` crate will use a fraction of its API surface area. Nightly rustc provides an option `-Zhint-mostly-unused` to tell it to defer as much compilation as possible, which provides a substantial performance improvement if most of that compilation doesn't end up happening. Cargo plumbs this option through using the new `[hints]` table. This will cause users of the `rustix` crate to default to setting `hint-mostly-unused`. (Top-level crates can override this if they wish, using a new profile option.) Note that setting this hint does not increase the MSRV of the rustix crate, as old versions of Cargo will ignore it. New versions of Cargo will respect it automatically (and, until we stabilize it, Cargo will do nothing unless you pass `-Zprofile-hint-mostly-unused` to cargo). Some sample performance numbers: this takes `rustix` compilation time with `all-apis` enabled from 5.9s to 4.3s (a 27% improvement). * Add comment to the mostly-unused hint
sunfishcode
pushed a commit
that referenced
this pull request
Jul 15, 2025
* Use new `hints.mostly-unused` Most users of the `rustix` crate will use a fraction of its API surface area. Nightly rustc provides an option `-Zhint-mostly-unused` to tell it to defer as much compilation as possible, which provides a substantial performance improvement if most of that compilation doesn't end up happening. Cargo plumbs this option through using the new `[hints]` table. This will cause users of the `rustix` crate to default to setting `hint-mostly-unused`. (Top-level crates can override this if they wish, using a new profile option.) Note that setting this hint does not increase the MSRV of the rustix crate, as old versions of Cargo will ignore it. New versions of Cargo will respect it automatically (and, until we stabilize it, Cargo will do nothing unless you pass `-Zprofile-hint-mostly-unused` to cargo). Some sample performance numbers: this takes `rustix` compilation time with `all-apis` enabled from 5.9s to 4.3s (a 27% improvement). * Add comment to the mostly-unused hint
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This is now released in rustix 1.0.8. |
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Most users of the
rustixcrate will use a fraction of its API surfacearea.
Nightly rustc provides an option
-Zhint-mostly-unusedto tell it todefer as much compilation as possible, which provides a substantial
performance improvement if most of that compilation doesn't end up
happening. Cargo plumbs this option through using the new
[hints]table. This will cause users of the
rustixcrate to default to settinghint-mostly-unused. (Top-level crates can override this if they wish,using a new profile option.)
Note that setting this hint does not increase the MSRV of the rustix
crate, as old versions of Cargo will ignore it. New versions of Cargo
will respect it automatically (and, until we stabilize it, Cargo will do
nothing unless you pass
-Zprofile-hint-mostly-unusedto cargo).Some sample performance numbers: this takes
rustixcompilation timewith
all-apisenabled from 5.9s to 4.3s (a 27% improvement).