bevy: Very high CPU usage with empty example using just default plugins

Bevy version

Tested on both 0.4 and recent master a8952569253c5712e890e250cd10c999c1a6b379.

Operating system & version

macOS 10.14 x86_64 (MacBook Pro 2014, 2c/4t 2.8GHz Intel Core i5). Latest nightly rustc, with the default rust linker (I haven’t installed lld).

What you did

I tested the following code on both versions mentioned above, in debug and release modes.

main.rs:

use bevy::prelude::*;

fn main() {
    App::build()
        .add_plugins(DefaultPlugins)
        .add_plugin(bevy::diagnostic::FrameTimeDiagnosticsPlugin::default())
        .add_plugin(bevy::diagnostic::LogDiagnosticsPlugin::default())
        .run();
}

Cargo.toml:

[package]
name = "city_simulator"
version = "0.1.0"
authors = ["nehalem501"]
edition = "2018"

[dependencies]
bevy = { git = "https://github.com/bevyengine/bevy", rev = "a8952569253c5712e890e250cd10c999c1a6b379" }

What you expected to happen

Have the app window show app with low CPU usage.

What actually happened

I have 100% CPU usage with this code when compiled in debug mode, and around 50% CPU usage in release mode. This seems very excessive for drawing an empty window and displaying a few log lines in a terminal. Am I doing something wrong ?

Additional information

These are the logs in debug mode, vsync seems to work:

Feb 17 09:27:18.040  INFO bevy_diagnostic::log_diagnostics_plugin: frame_time  : 0.017584    (avg 0.016661)
Feb 17 09:27:18.040  INFO bevy_diagnostic::log_diagnostics_plugin: fps         : 59.463637   (avg 59.926370)
Feb 17 09:27:18.040  INFO bevy_diagnostic::log_diagnostics_plugin: frame_count : 227.000000  (avg 227.000000)

And these the logs in release mode:

Feb 17 09:44:54.987  INFO bevy_diagnostic::log_diagnostics_plugin: frame_time  : 0.017124    (avg 0.016655)
Feb 17 09:44:54.987  INFO bevy_diagnostic::log_diagnostics_plugin: fps         : 60.254282   (avg 60.020315)
Feb 17 09:44:54.987  INFO bevy_diagnostic::log_diagnostics_plugin: frame_count : 1605.000000  (avg 1605.000000)

Screenshot of System Monitor with the debug version: Screenshot 2021-02-17 at 09 29 39

Screenshot of System Monitor with the release version: Screenshot 2021-02-17 at 13 34 36

About this issue

Original URL
State: closed
Created 3 years ago
Reactions: 9
Comments: 37 (11 by maintainers)

Most upvoted comments

briefly puts on world-weary project owner hat however given the frequency of percent-cpu-usage-related issues, maybe we should optimize for public perception anyway, despite the facts of the situation

cart on Mar 5, 2021

@geNAZt

I consider that to be a separate issue. The many sprites example is a intended to be stressful (and we are already in the process of optimizing it). This thread is about “baseline” cpu usage when nothing is happening.

cart on May 14, 2021

I agree that using CPU percentage for measuring performance of big multithreaded apps is not very serious. But an empty project with just the default plugins shouldn’t make a laptop fan spin at full speed.

If I write minimal C code to show a window and call glClear at 60hz, I expect it to not be very demanding and not use 60% of my CPU. Bevy is of course much more complex, so I expect more bloat than this very simple example, but if I write a game, I want most resources to be used on this game’s complex algorithms, not on the framework.

Please don’t view this as a rant, I’m just trying to understand what is going on.

nehalem501 on Mar 5, 2021

How about CPU temps? 😝

I am definitely not getting 60 fps on a high end macbook pro with really simple bevy projects so something is wrong.

samnm on Mar 5, 2021