Interleave downloads with installations when downloading a toolchain #4471

FranciscoTGouveia · 2025-09-05T15:33:38Z

Continuation of #4436.

This change aims to speed up the overall performance of the rustup [toolchain] install command by allowing the installation of a component to start immediately after its download completes.
This approach is particularly beneficial for slower connections, as it enables installations to progress in parallel with ongoing downloads -- so by the time all downloads are finished, all installations should be completed as well.

NB: This PR is not yet ready for review. I believe this change should be backed by benchmarks and user feedback before moving forward. I’ll share those here in the next couple of days.

src/dist/manifestation.rs

tests/suite/cli_rustup.rs

rami3l · 2025-09-10T14:04:27Z

src/dist/notifications.rs

                }
            }
+            ComponentInstalled(c, h, t) => {
+                if Some(h) == t.as_ref() || t.is_none() {


Nit: Now that we are at it, I would probably give an extra commit to avoid the t.unwrap() here by flipping the if and writing something like:

if let Some(t) = t && t != h { ... } else { ... }

I did this based on how other Notifications were being handled.
Should I refactor all of them now, leave that for another PR, or just change this one?

@FranciscoTGouveia It should be worthwhile to refactor them all in a separate commit (before your addition) lest we forget about it :)

If you agree, I would like to leave this for a follow-up PR, right after this one is merged.
So I suggest leaving this as unresolved for now.

Okay, let's do #4471 (comment) for the particular change in this PR, and then move the rest to that style in a subsequent PR.

src/cli/download_tracker.rs

src/dist/manifestation.rs

FranciscoTGouveia · 2025-09-17T22:10:34Z

As noted in the opening message of the PR, I now present some benchmarks that will enable us to move forward with this change.
As stated before, this will bump the install and update commands' performance, as when the downloads finish, the installations have already executed.

The results are presented in the plot below, for both low-speed and high-speed internet connections.

These results were obtained by running the rustup toolchain install nightly command 10x times for each combination of variables (RUSTUP_CONCURRENT_DOWNLOADS, interleaved or not, and internet connection).
Please note that the y axis do not start on zero, and cannot be directly compared between themselves.

Below, I also leave a small animation of the previous and current behavior of the rustup toolchain install command to illustrate the UX changes that this PR also implies.
On the left you can see the previous version and on the right, the version with the interleaved installations.
Please note that this is just an animation and does not have the purpose of showing any kind of speedup.

Thanks for taking the time to review this PR!

src/config.rs

src/dist/component/package.rs

src/dist/download.rs

src/dist/temp.rs

rami3l

Modulo the previously requested changes and the two extra nits, I think this PR is quite ready. Thanks a lot, @FranciscoTGouveia!

src/dist/manifestation.rs

src/cli/common.rs

…e function

Even though downloads are done concurrently, the installations are done sequentially. This means that, as downloads complete, they are in a queue (an mpsc channel) waiting to be consumed by the future responsible for the (sequential) installations. There was a need to relax some test cases to allow for uninstall to happen before the downloads.

…ation with a download

…how a component was installed

…ready downloaded

…hread installations Co-authored-by: rami3l <[email protected]>

…nue during installations Co-authored-by: rami3l <[email protected]>

djc · 2025-09-19T11:56:46Z

src/dist/manifestation.rs

+        component: Component,
+        format: CompressionKind,
+        installer_file: File,
+        tmp_cx: &temp::Context,
+        download_cfg: &DownloadCfg<'_>,
+        new_manifest: &Manifest,
+        tx: Transaction<'a>,


I think the number of arguments is here too large, and this should be rethought to have a named field struct that can hold all/most of the arguments.

I think the pre-existing code here could benefit from some refactoring as well, for example by packaging together the arguments passed into the compression wrappers. The uninitialized variables structure also sounds out as pretty unidiomatic.

djc · 2025-09-19T11:58:14Z

src/dist/manifestation.rs

+                    let download_tx_cloned = download_tx.clone();
+                    async move {
+                        let _permit = sem.acquire().await.unwrap();
+                        self.download_component(


Pre-existing, but this argument list is also just too long, and I think we should find a different way to express this before layering on more complexity.

djc · 2025-09-19T11:59:20Z

src/dist/manifestation.rs

+
+            let semaphore = Arc::new(Semaphore::new(concurrent_downloads));
+            let component_stream =
+                tokio_stream::iter(components.into_iter()).map(|(component, format, url, hash)| {


Suggest writing this closure as a named function.

djc · 2025-09-19T11:59:25Z

src/dist/manifestation.rs

+
+            let mut stream = component_stream.buffered(components_len);
+            let download_handle = async {
+                let mut hashes = Vec::new();


Suggest writing this as a named function.

djc · 2025-09-19T11:59:36Z

src/dist/manifestation.rs

+                }
+                hashes
+            };
+            let install_handle = async {


Suggest writing this as a named function.

djc · 2025-09-19T12:00:33Z

src/cli/download_tracker.rs

+            .keys()
+            .find(|comp| comp.contains(component))
+            .cloned();
+        if let Some(key) = key


Nit: invert these for early returns.

djc · 2025-09-19T12:01:16Z

src/cli/download_tracker.rs

+    }
+
+    /// Notifies self that the component has been installed.
+    pub(crate) fn component_installed(&mut self, component: &str) {


Can we share the duplicate code?

djc · 2025-09-19T12:02:06Z

src/dist/notifications.rs

+                if let Some(t) = t
+                    && t != h
+                {
+                    write!(f, "installing component '{c}' for '{t}'")
+                } else {
+                    write!(f, "installing component '{c}'")
+                }


Nit: I think this would look better as a match:

match t { Some(t) if != h => write!(f, ..), _ => write!(f, ..), }

djc · 2025-09-19T12:03:14Z

src/cli/download_tracker.rs

+            ProgressStyle::with_template(if pb.position() != 0 {
+                "{msg:>12.bold}  downloaded {total_bytes} in {elapsed}"
+            } else {
+                "{msg:>12.bold}  component already downloaded"
+            })
+            .unwrap(),


Again there's a lot of duplication here, suggest adding a little abstraction to make it more obvious what happens here.

djc · 2025-09-19T12:05:17Z

src/dist/component/transaction.rs

-    tmp_cx: &'a temp::Context,
-    notify_handler: &'a dyn Fn(Notification<'_>),
+    changes: Vec<ChangedItem>,
+    tmp_cx: Arc<temp::Context>,


Seems to me that tmp_cx, notify_handler and process should be bundled up together.

djc · 2025-09-19T12:06:58Z

Very excited about these performance improvements! Personally I don't really feel comfortable with the added complexity in the current changes -- I think there should be some more refactoring before this can be cleanly added.

FranciscoTGouveia force-pushed the install-after-download branch from c4b68b2 to c2954ba Compare September 5, 2025 16:02

rami3l self-assigned this Sep 6, 2025

rami3l mentioned this pull request Sep 7, 2025

fix(cli/rustup_mode): use ASCII-compatible spinner #4473

Merged

FranciscoTGouveia force-pushed the install-after-download branch from c2954ba to 1d7e5f5 Compare September 10, 2025 13:27

rami3l reviewed Sep 10, 2025

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rami3l reviewed Sep 16, 2025

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FranciscoTGouveia force-pushed the install-after-download branch 2 times, most recently from 947b8da to 9e5d0e0 Compare September 16, 2025 10:40