High CPU usage while running on OS X

[dceddia]

After running npm start, the node process consumes ~40% CPU on my machine:

I found that setting a polling interval in the the WebpackDevServer helped:

new WebpackDevServer(compiler, {
    historyApiFallback: true,
    hot: true, // Note: only CSS is currently hot reloaded
    publicPath: config.output.publicPath,
    quiet: true,

    // added this:
    watchOptions: {
      poll: 1000
    }
  })

Here were the settings I tried, and the resulting CPU usage:

poll: 1000  =>  4-6% CPU
poll: 500   =>  8-10% CPU
poll: 250   =>  14-16% CPU

There's a tradeoff between CPU usage and how snappy the dev experience feels. To me, 1000ms felt sluggish, but 500ms felt pretty good. I couldn't discern much difference between 500ms and 250ms.

It seems like adding some kind of polling interval would be a good idea to reduce the CPU usage.

[gaearon]

I wonder if we should just do something like this: https://github.com/researchgate/webpack-watchman-plugin

[gaearon]

Does webpack always use poll mode? Or only when it couldn’t use fsevents? Or are these two unrelated things?

[dceddia]

That's a good question. As far as I can tell poll defaults to true, which apparently means "poll like crazy". It also seems to watch everything in node_modules by default -- adding this ignore line cuts CPU usage to near-zero, even while leaving poll at its default setting:

watchOptions: {
  ignore: /node_modules/
}

I'm not sure if this is a good idea, since I noticed that webpack.config.dev.js has a few loaders that seem to depend on paths.appNodeModules, which I assume is the node_modules directory?

As another data point, my wife also has a Mac and hers doesn't exhibit the high CPU usage while running npm. Different version of OS X (10.9 instead of 10.10) but I'm not sure what else is different.

Update: I'm also sad to report that node has stopped showing high CPU usage on my machine now, too. Sad because... what changed?

[gaearon]

Hmm we definitely don't want to watch node_modules (even though we allow importing CSS from them). If we do, it's an issue and we need to fix it.

[gaearon]

I'll accept a PR adding ignored (not ignore by the way) to watcher settings. webpack/watchpack#23

[gaearon]

This was fixed by #294.

[gaearon]

This should be fixed in the new version. Can you please verify?
Please find the upgrade instructions here.

[dceddia]

Just tried it: node CPU usage now hovers between 0.1 and 0.2% 👍

[shauntrennery]

Seems to be a problem again with Node 7.0.0 and 7.1.0. macOS Sierra reporting CPU usage of 110% during "npm start" operation.

[ggregoire]

Can confirm here.

I updated from node 6.8.1 to node 7.1.0 yesterday and now the node process consumes 100% CPU on my machine.

I didn't find anything relative to CPU usage and node 7 in Webpack issues.

I'm on El Capitan + latest version of CRA.

@gaearon @dceddia Should we reopen the issue or create a new one?

Edit: For those who have the same problem, you can downgrade with brew switch node x.x.x and list all the versions installed with brew info node.