Doing the Least Amount of Work Possible: An Intro to Runtime Performance

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In this talk we’ll explore a variety of techniques one can employ to ensure that their apps are running at peak performance. With a couple of small tweaks, you can make perf a built-in.

Ken Wheeler
Ken Wheeler
35 min
14 May, 2021

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Video Summary and Transcription

This Talk on runtime performance covers various aspects such as understanding and fixing performance issues, optimizing performance and perceived performance, profiling runtime performance, analyzing performance and debugging memory leaks, and dealing with memory leaks. It also discusses the use of dev tools, CSS transforms, and layout in improving performance. The Q&A session addresses questions about libraries like Immutable.js, common trends in memory leaks, and the impact of animations on performance.

Available in Español

1. Introduction to Runtime Performance

Short description:

Hey, everybody. My name is Ken and I am here today to talk about runtime performance. Let's get started by asking what is runtime performance. When we're talking about performance, we often focus on load performance, like site speed, bundle sizes, and parsing JavaScript. Time to interactive is crucial for users to start using your app or site.

Hey, everybody. My name is Ken and I am here today to talk about runtime performance. This is my talk, doing the least amount of work possible, which, while not only a performance tenet is a personal value that I hold.

So, let's get started by asking what is runtime performance. And you don't hear as much of it comparatively to some of the other stuff, right? A lot of the time when we're talking about performance, when you hear from, you know, I guess what would be devrels or platform advocates, the performance that they're advocating for is your load performance, right? Like a lot of conversion and retention and things like that. That all boils down to how fast your site loads and, you know, your time to interactive and things like that. You have all these lighthouse metrics and that's what's largely optimized for, right? You know, you're seeing things tooling like lighthouse scores, core web vitals now built into create React app. Things like page weight, right? Everyone's concerned with bundle splitting and keeping your bundle sizes in control. And that also funnels into things like the time it takes to parse JavaScript, like if you have a lot of JavaScript you're serving up, right? First contentful paints, right? You have these benchmarks of how fast your site's coming in and most importantly, I think, is time to interactive, which is the time until someone can actually start using your app or your site. They're in the clear to get going.

2. Understanding Performance Issues and Fixes

Short description:

While this talk is not about load performance, it focuses on staying interactive and not blocking the main thread. Issues like computationally expensive tasks, animations, parsing, and memory leaks can adversely affect the user experience. Slow performance, dropped frames, and input delay are indicators of a problem. Fixing performance issues often requires detective work.

While that's super important metrics and it's very well documented, that's not what this talk is about. This is about staying interactive, right? Once you've loaded up, once you've covered your bases, depending on what your app or your site does, what you want to do at the end of the day is continue to be interactive after you've gotten them to that meaningful checkpoint, right? And the core piece of that is to not block your main thread.

In JavaScript, you have a main thread, and it's where a lot of the party goes on. And if you block it, you're going to see things like animations are going to jank out, you're going to be typing into inputs, and there's going to be lag. All things that adversely affect the UX of your site or app, and you don't want that. So the typical issues that you might see, things like computationally expensive tasks, if you have to operate on or clone a big bunch of objects or something like that, animations is where you'll see it. A lot of the time, you got to go and start typing or start trying to click something or do a hover to see it, but if you have an animation going on, you're going to see that almost immediately if it's done a certain way, so it's going to jank out. And it doesn't even have to be like, you know, 900,000 objects. You can have your whole site get janked out just by Reflow, Repaint, and Layout. I was looking at a site for a buddy the other day, and he didn't have any JavaScript, but the site was running slow. And it was the web animations API, it was just browser layout taking place. All right? You know, other things are parsing, right? If you're parsing large buffers or JSON, right, that takes time. That's a computationally expensive task. And my least favorite of all, which you probably have the least insight into and takes real detective work is memory leaks. They're devastating. But again, that's that becomes really apparent. Oftentimes not very quickly. You have to sit there for, you know, an hour, and now the thing slows down. And then you say, oh, boy, like, you know, you have like a CSS problem, you refresh, and you can say, I changed this, I changed that with a memory leak. You have to wait an hour just to reproduce it. It's rough.

So how do you know that you have a performance issue? So I mean, obviously, you write your profile, but a lot of the time, if it's actually an issue, you'll know. Like, you know, as far as you hear a lot of talk about premature optimization, things like that. If you have a performance issue, a lot of the time, it becomes pretty apparent. Your thing will be slow, you know, unless you get used to it being slow. But that's a whole other talk, right? Your best case scenario is you're going to see a lot of dropped frames and things like input delay, right? Those will be the main indicators that you're having a problem. Your worst case scenario is an aw snap, right? And then this is where it memed out, and you know, it's totally crashing your website. So those two points and anywhere in between, it's indicative that, you know, you should probably take a look at the code and think about optimizing it.

So how do you fix it? You've identified that there is a problem. You're not sure what it is, but how do you fix it? And I'll tell you right now that a lot of it is like detective work.

QnA

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