Empty game (no logic) has 50% CPU usage and low FPS (40+ instead of 60) on iOS

[wentao]

Bevy version

Tested on both 0.14.2

[Optional] Relevant system information

Tested on

• iPhone 16 Simulator
• iPhone 13

If your bug is rendering-related, copy the adapter info that appears when you run Bevy.

AdapterInfo { name: "Apple A15 GPU", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }

What you did

I setup a bare minimum project to demonstrate the issue https://github.com/80gen/bevy_ios_bug/tree/cpu_high

What went wrong

The game logic doesn't have anything, not even a camera setup, see https://github.com/80gen/bevy_ios_bug/blob/cpu_high/crates/game/src/lib.rs

When running the game on desktop (in my test it's Macbook Pro M1), it looks fine, with CPU usage at 10%. No error log.

But when the game run in either iOS Simulator or physical phone, the CPU usage stay above 50% and FPS average at 40 (should be 60).

Here is a screenshot from the XCode debugger

The XCode terminal is showing the following log

AdapterInfo { name: "Apple iOS simulator GPU", vendor: 0, device: 0, device_type: DiscreteGpu, driver: "", driver_info: "", backend: Metal }
AddInstanceForFactory: No factory registered for id <CFUUID 0x600000245a60> F8BB1C28-BAE8-11D6-9C31-00039315CD46
Failed to start Gilrs. Gilrs does not support current platform.
processing non `RedrawRequested` event after the main event loop: AboutToWait
Creating new window "App" (0v1#4294967296)
`WindowAttributes::min_inner_size` is ignored on iOS
`Window::theme` is ignored on iOS
processing non-`RedrawRequested` event after the main event loop: WindowEvent {
    window_id: WindowId {
        window: 0x0000000105a9fd30,
    },
    event: Focused(
        true,
    ),
}
processing non-`RedrawRequested` event after the main event loop: WindowEvent {
    window_id: WindowId {
        window: 0x0000000105a9fd30,
    },
    event: Resized(
        PhysicalSize {
            width: 3840,
            height: 2160,
        },
    ),
}
processing `RedrawRequested` during the main event loop
processing non `RedrawRequested` event after the main event loop: AboutToWait
"finished frame"  tracy.frame_mark=true
processing `RedrawRequested` during the main event loop
processing non `RedrawRequested` event after the main event loop: AboutToWait
"finished frame"  tracy.frame_mark=true
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
processing non `RedrawRequested` event after the main event loop: AboutToWait
"finished frame"  tracy.frame_mark=true

And this line get repeated infinitely

�[2m2024-12-09T23:09:26.510999Z�[0m �[33m WARN�[0m �[2mwinit::platform_impl::ios::app_state�[0m�[2m:�[0m processing non `RedrawRequested` event after the main event loop: AboutToWait
�[2m2024-12-09T23:09:26.513511Z�[0m �[33m WARN�[0m �[2mwinit::platform_impl::ios::app_state�[0m�[2m:�[0m processing non `RedrawRequested` event after the main event loop: AboutToWait

[alice-i-cecile]

This is probably the same / similar root cause as #10261, and due to a faulty windowing event loop somehow.

[wentao]

Did more testing, and noticed somehow I can't get anything to render on 0.15, so I updated this bug to be reproduce-able on 0.14.2 for now.

[wentao]

This is probably the same / similar root cause as #10261, and due to a faulty windowing event loop somehow.

I don't think so. I've tested this on my Macbook Pro M1 and the CPU usage is around 10%. The issue with CPU and FPS only happens on iOS.

[wentao]

Sorry I have to take my words back. Tested on Macbook Pro M1 and the CPU is around 40% (not 10%). This time I'm using examples from https://bevyengine.org/examples/3d-rendering/3d-scene/