CPU Spike - Ingestion suggestions

[data-sync-user]

We have a large spike in CPU exceptions that correlates with this experiment. It started around May 1st.

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┆Issue is synchronized with this Jira Task

[linabutler]

I think the "CPU exception" is a diagnostic that's emitted whenever the app is using too much CPU time in the background, and the OS terminates it—it's not a typical user-visible crash.

I think the high CPU usage might be caused by SuggestStore.ingest() blocking the main thread until it's done. ingest() is called from the RustFirefoxSuggest actor, but, per @OrlaM's comment here, actors aren't really appropriate for this—we should be using a dispatch queue instead, and awaiting its result via withCheckedContinuation to make it play well with async/await.

Once we have a SuggestStore.interruptEverything() API (https://bugzilla.mozilla.org/show_bug.cgi?id=1897264) in the Rust component, we can change iOS to:

• Call SuggestStore.ingest() and SuggestStore.query() on a (concurrent) dispatch queue.
• Add an expirationHandler to our background ingestion task, that calls the new interruptEverything() API.

[linabutler]

Call SuggestStore.ingest() and SuggestStore.query() on a (concurrent) dispatch queue.

Nitpicking my own analysis (🧐): it's almost definitely more efficient to use a pair of serial queues for this (with appropriate QoS), than a concurrent queue. There's a bit more about that captured here.

[data-sync-user]

➤ Norberto Andres Furlan commented:

Lina Butler to confirm if we can have this for FX 127.

CC: Nive Suresh Orla Mitchell

[data-sync-user]

➤ Diana Andreea Barladeanu commented:

Hi, Lina Butler ! What should QA test in this ticket? Thanks!

[data-sync-user]

➤ Lina Butler commented:

Hi Diana Andreea Barladeanu! 👋 I think just a smoke test that enables the Cross-Platform Suggest experiment, and makes sure that the suggestions are eventually ingested and show up in the address bar, would be sufficient for testing. This ticket reworked the implementation, but the user-facing experience should be the same. Thanks!

[data-sync-user]

➤ Diana Andreea Barladeanu commented:

Validated on v127 (42448), with iPhone 15 (17.4.1).

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