https://perfht.ml/2w4zbUp When inserting RDM icon in the toolbox toolbar, we end up loading responsivedesign.jsm which takes 3.9ms / 1.2% of overall JS computing in parent process.

With this patch we go down to 0.5ms / 0.2% for loading responsivedesign.jsm: https://perfht.ml/2w577A1

This patch moves most of devtools/client/responsivedesign/responsivedesign.jsm to devtools/client/responsivedesign/responsivedesign-old.js as it is all related to the old RDM. Then, I added lazy loading in devtools/client/responsive.html/manager.js so that we end up only loading a very small responsivedesign.jsm and only manager.js (and none of its deps).

No particular win reported by DAMP: https://treeherder.mozilla.org/perf.html#/comparesubtest?originalProject=mozilla-central&newProject=try&newRevision=0e3164dff0d4853595075f0a1c46f18abd154d53&originalSignature=edaec66500db21d37602c99daa61ac983f21a6ac&newSignature=edaec66500db21d37602c99daa61ac983f21a6ac&filter=.open&framework=1&selectedTimeRange=172800 (Anything under 5% win is most likely invisible to DAMP)

Comment on attachment 8907043 [details] Bug 1399090 - Lazy load responsive design manager modules. https://reviewboard.mozilla.org/r/178768/#review183992 Thanks, looks like a good cleanup and perf improvement! :) It seems like we could go further though, maybe in a follow up bug / patch. Is there any reason for the new vs. old switch to be a JSM? Can we convert it to a regular module instead? I also noticed some references to RDM in `browser.js` that seem like dead code now that DevTools manages menus and shortcuts: http://searchfox.org/mozilla-central/rev/51eae084534f522a502e4b808484cde8591cb502/browser/base/content/browser.js#8467-8477 (Perhaps the Scratchpad part is dead as well.) ::: devtools/client/responsivedesign/responsivedesign-old.js:1 (Diff revision 2) > -"use strict"; > - > -const Cu = Components.utils; > - > -const { loader, require } = Cu.import("resource://devtools/shared/Loader.jsm", {}); > const { LocalizationHelper } = require("devtools/shared/l10n"); New file needs license header. ::: devtools/client/responsivedesign/responsivedesign-old.js:130 (Diff revision 2) > } > }) > }; > > EventEmitter.decorate(Manager); > +exports.Manager = Manager; Rename the `Manager` object to `ResponsiveUIManager` in the new file. This way both new and old use the same name. (I only changed to `Manager` when adding the new / old switch because of some ESLint rule.) ::: devtools/client/responsivedesign/responsivedesign-old.js:259 (Diff revision 2) > > this.showNewUINotification(); > > // Notify that responsive mode is on. > this._telemetry.toolOpened("responsive"); > - ResponsiveUIManager.emit("on", { tab: this.tab }); > + Manager.emit("on", { tab: this.tab }); These renames can all be reverted with the name change above.

(In reply to J. Ryan Stinnett [:jryans] (use ni?) from comment #6) > Comment on attachment 8907043 [details] > Bug 1399090 - Lazy load responsive design manager modules. > > https://reviewboard.mozilla.org/r/178768/#review183992 > > Thanks, looks like a good cleanup and perf improvement! :) > > It seems like we could go further though, maybe in a follow up bug / patch. > Is there any reason for the new vs. old switch to be a JSM? Can we convert > it to a regular module instead? Opened bug 1399449. > I also noticed some references to RDM in `browser.js` that seem like dead > code now that DevTools manages menus and shortcuts: > > http://searchfox.org/mozilla-central/rev/ > 51eae084534f522a502e4b808484cde8591cb502/browser/base/content/browser. > js#8467-8477 > > (Perhaps the Scratchpad part is dead as well.) That's bug 1250832, I think I will proceed with all these cleanups early during 58 cycle.

Pushed by apoirot@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/665aadca9d5f Lazy load responsive design manager modules. r=jryans