{"action":"opened","issue":{"url":"https://api.github.com/repos/atom/atom/issues/10920","repository_url":"https://api.github.com/repos/atom/atom","labels_url":"https://api.github.com/repos/atom/atom/issues/10920/labels{/name}","comments_url":"https://api.github.com/repos/atom/atom/issues/10920/comments","events_url":"https://api.github.com/repos/atom/atom/issues/10920/events","html_url":"https://github.com/atom/atom/issues/10920","id":135264738,"number":10920,"title":"Tab Switching Performance Unacceptably Slow","user":{"login":"jordwalke","id":977348,"avatar_url":"https://avatars.githubusercontent.com/u/977348?v=3","gravatar_id":"","url":"https://api.github.com/users/jordwalke","html_url":"https://github.com/jordwalke","followers_url":"https://api.github.com/users/jordwalke/followers","following_url":"https://api.github.com/users/jordwalke/following{/other_user}","gists_url":"https://api.github.com/users/jordwalke/gists{/gist_id}","starred_url":"https://api.github.com/users/jordwalke/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jordwalke/subscriptions","organizations_url":"https://api.github.com/users/jordwalke/orgs","repos_url":"https://api.github.com/users/jordwalke/repos","events_url":"https://api.github.com/users/jordwalke/events{/privacy}","received_events_url":"https://api.github.com/users/jordwalke/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2016-02-21T21:54:08Z","updated_at":"2016-02-21T21:54:08Z","closed_at":null,"body":"### Prerequisites\r\n\r\n* [ x] Can you reproduce the problem in [safe mode](https://atom.io/docs/latest/hacking-atom-debugging#check-if-the-problem-shows-up-in-safe-mode)?\r\n* [ x] Are you running the [latest version of Atom](https://atom.io/docs/latest/hacking-atom-debugging#update-to-the-latest-version)?\r\n* [ x] Did you check the [debugging guide](https://atom.io/docs/latest/hacking-atom-debugging)?\r\n* [x ] Did you check the [FAQs on Discuss](https://discuss.atom.io/c/faq)?\r\n* [x ] Are you reporting to the [correct repository](https://github.com/atom/atom/blob/master/CONTRIBUTING.md#atom-and-packages)?\r\n* [ x] Did you [perform a cursory search](https://github.com/issues?q=is%3Aissue+user%3Aatom+-repo%3Aatom%2Felectron) to see if your bug or enhancement is already reported?\r\n\r\nFor more information on how to write a good [bug report](https://github.com/atom/atom/blob/master/CONTRIBUTING.md#how-do-i-submit-a-good-bug-report) or [enhancement request](https://github.com/atom/atom/blob/master/CONTRIBUTING.md#how-do-i-submit-a-good-enhancement-suggestion), see the `CONTRIBUTING` guide.\r\n\r\n### Description\r\n\r\nTab performance is unacceptably slow. The issue might be masked on top of the line computers, but on my average (new Macbook 12\") it is far too slow. I've performed some profiling and have pasted some screenshots of that profiling. Even with raw text files (no syntax highlighting), at least 62ms is spent purely in JS and DOM manipulation, layout and compositing. I see several forced layouts (one of which takes `13ms` by itself). \r\nBut if those changes happen to end right at the tail end of screen display vsync, that could incur as much as another `16ms` to the latency totaling at least `78ms` (assuming I have a 60hz display). (On average it will be an additional `8ms` though).\r\n\r\nThis alone is beyond the threshold of human perceivable delay, but then these changes still take time to go from the graphics system to my display, and doesn't account for my keystroke from USB keyboard to the Atom process itself, so the total effect might be as much as `100ms` delay. I'll admit, even though I can only measure about `70ms` of delay, it *feels* slower than that - so a large effect here might be attributed to something in the Electron/application infrastructure that escapes our measurement.\r\n\r\n### Steps to Reproduce\r\n\r\n(The file navigation tree is open fwiw)\r\n1. [Open several files]\r\n2. [Switch Tabs]\r\n3. [experience slowness]\r\n\r\n**Expected behavior:** [What you expected to happen]\r\nFast Tab Switching.\r\n\r\n**Actual behavior:** [What actually happened]\r\nSlow Tab Switching.\r\n\r\n### Versions\r\n1.5.3 Running Atom in `--safe` mode\r\n\r\n"}}