Use new hints.mostly-unused to speed up compilation
#4208
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Most users of the AWS SDK crates will use a fraction of their API surface area. Nightly rustc now 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 AWS SDK crates 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 AWS SDK crates, 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 `aws-sdk-ec2` compilation time ~4m07s to ~2m04s, a ~50% speedup.
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This is a most welcome PR so first thank you. We've been discussing for a while now how we're going to improve compile times for the SDK crates but working on the compiler is not our area of expertise and some service models like EC2 are just large and there will only be so much we can do on our side.
Happy to help try and work through the gradle issues, relying on CI is fine as well though.
| @@ -138,6 +139,7 @@ fun testRustSettings( | |||
| moduleAuthors, | |||
| moduleDescription, | |||
| moduleRepository, | |||
| hintMostlyUnused, | |||
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ought to be something like
...
license,
examplesUri,
minimumSupportedRustVersion = null,
hintMostlyUnused,
)
|
Reading through the proposed blog post on this feature and the corresponding Zulip thread I wonder if it would be best to scope this change to just a few of our larger more compilation heavy crates to begin? The blog says:
Compilation improvements are a frequent ask from our users (see the most upvoted issue on the aws-sdk-rust repo), so this is definitely something we want, and I think the intent here applies to some of the more popular AWS crates, especially ones that combine control/data plane operations in a single client (EC2, S3, DDB). But I don't know that we would want this on all crates from the outset without a ton of benchmarking of customer applications. Since this is such a high user priority if you don't feel like you have the comfort with Kotlin (or desire/free time to develop it) to scope this we can discuss taking over the work on our team. If you were interested in doing the work it would probably look something like a simple decorator customizing the manifest that is registered in AwsCodegenDecorator and only targets a few specific services. |
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Love the overall direction! We can definitely massage this on our end, if needed. As Landon says, having an allow list for target services and making the list configurable through codegen settings might be desirable (like the one we used to have for event streams). |
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I'd be happy to see this taken over by someone familiar with both Kotlin and the code generator. And it seems fine to scope this to just the biggest crates; it wouldn't make sense, for instance, for a crate with only a couple of functions. |
Awesome, thanks for bringing this new feature to our attention. I will take over this work in a week or two when I clear out my current tasks. |
Most users of the AWS SDK crates will use a fraction of their API
surface area.
Nightly rustc now provides an option
-Zhint-mostly-unusedto tell itto 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 AWS SDK crates 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 AWS SDK
crates, 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
aws-sdk-ec2compilationtime ~4m07s to ~2m04s, a ~50% speedup.
Please note that this change to the code generator is the first Kotlin code
I've ever written, and I can't seem to get gradle to run locally in order to
test it, so this is a draft. I've extensively tested the addition of the
hintstable manually, but I'm currently relying on CI to verify that thisproduces the expected
Cargo.tomlchanges for theaws-sdk-*crates.Checklist
.changelogdirectory, specifying "client," "server," or both in theapplies_tokey..changelogdirectory, specifying "aws-sdk-rust" in theapplies_tokey.By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.