How to Optimize Performance in Unreal Engine 5

welcome friends I'm new all game projects have to deal with performance issues budgets get blown frame targets are missed and FPS tanks today's video has two parts first we're going to look at unreal's Main profiling tool unreal insights is super powerful I'll show you how it works and I'll teach you how to diagnose and fix perf problems in your game second we're going to look at a real world example I've got a nasty perf bottleneck in my time rewinding project why is my game running at 20 frames per second we're going to profile it to find out and then we're going to fix it let's get started unreal insights and tracing functionality now live down in the bottom right of the editor if you're in an older version of the engine you'll need to look around in the tools menu to launch unreal insights we click on trace and then go to Unreal insights session browser this will pull up the session browser which shows all of the traces that we've captured if we've never captured a trace it's completely empty to Capt capture a trace we click the button next to the trace menu to start tracing that will turn red which shows us that we're tracing and if we look at the session browser we now see that we have an entry its status is live and the file size is rapidly increasing I'm going to go ahead and stop tracing before I look at my actual Trace file with that done we can doubleclick on the entry and this will launch on real insights the insights application shows us a ton of performance information across a of different panes and we will go through everything but we're mostly going to be looking at this timeline view or this timing view here in the center within the timing pane you can zoom in and out by using the mouse wheel and you'll notice right away that my editor has been running for quite a while because I I went and got lunch and left it up you can pan left and right by clicking and dragging and you can zoom back in by scrolling in within this view we have a bunch of different tracks so at the top here I have a GPU track I have a track for my game thread track for the rhi thread the render thread a bunch of worker threads basically every thread that is running in my editor process and for each track we have a flame graph so if you've never used a flame graph before it basically goes top to bottom and we can look here at the top and we can see okay we have a frame on the game thread within that frame we ticked the world we drew the viewport slate ticked that slate tick called slate draw Windows which turns around and called slate prepass so on and so forth so we can basically drill into a bunch of deeper calls and as long as those calls are instrumented we can see what they were doing and how much time they spent in this top pane we have timings for all the different frames in our capture the bigger the bar the longer the frame so if I wanted to look at this one fat frame I can see it took 52 1 12 milliseconds which is about 19 frames per second I can left click on that to jump to it and then if I press the F key it's going to focus my timeline view to look at that frame specifically so here I can see I actually spent 26 milliseconds pumping Windows messages this is probably well I don't know what was going on there I would need to to drill in but this is a really long frame along the top view of timing we have a timeline which is the time since the process started we have a bunch of dropdowns which allow us to turn tracks on and off so for some reason I didn't want to look at say the game thread I can just turn that off and turn it back on note for something to show up in this list I have to be capturing it and we'll we'll talk about how you can figure what you're capturing a little bit later the CPU GPU menu also gives you groupings to filter so if I want to turn off all the background workers I can make them disappear like that other has some additional things that we can look at plugins has some other special things as well but basically this is just allowing us to turn things on and off for filtering another hotkey that is super useful is you can tap C to toggle between full View and compact view so if I wanted to get a compact picture of everything that was going on I can tap see and you can look for basically big chunks of color that might be interesting to into and to go back to the full view we just tap C again in addition to the timing view down at the bottom here we have a view of logs and any important events and if we doubleclick it will take us to that position in the timeline so that we can drill in over on the right we have counters and timers I find timers are generally the most useful if I want to look at what happened in a frame I can click on any of the tracks in my flame graph that will select it in the timer view I can look at inclusive and exclusive time and I can also get a full picture of who called whatever my selection is so that's callers we can see here that engine Loop tick called frame which called slate tick which called slate draw Windows which called slate prepass and I can also look at Coles which is everything that the thing I have selected calls in this case slate prepass has widget inv validate called 14 times but these timings are all all tiny 4 and 1/2 micros seconds so there's a whole bunch of stuff going on in slate prepass that that isn't instrumented and if I wanted to investigate this what I would begin doing is instrumenting that code path and and seeing the details of what is going on a couple other cool things that we can do here I can take a snapshot there is a continuous running buffer in the editor and when we click this button it will snap that buffer and create a trace just with those details so this is useful if like let's say I'm playing the game I have a big perf hitch but I wasn't actively tracing I can take a snapshot to see what was there and then you know open it up just like our first trace and we we could see what was going on few other things tracing there's a whole bunch of different channels that we can choose what we want to look at right now I am using the default so CPU GPU some regions bookmarks some other things while a trace is running we can capture bookmarks and screenshots which I'll show you so first let me do a bookmark which I can do from this menu and I can also do a screenshot from this menu or press contrl plus F9 I'm going to stop my Trace I'm going to come back to the session browser we're going to look at our most recent trace and on this this timeline view once we get back to where we were you will see hey there's a bookmark here with a timestamp and that will also show up in our log view here so that was when I pressed that bookmark button and that gives me a clear visual indicator of what was going on there I also have the screenshot right here on this timeline so if I hit a bug or a performance issue and I wanted to take a screenshot so that I could remember what was going on at that point in time we can do that with Control Plus F9 while tracing and similarly that is also down here in our log view so this allows us to really explore and get a full view of what unreal was doing and we can look retroactively we can make changes we can measure things over time other things that are useful to know running in the editor we have a whole bunch of stuff running that is not our game if we want really representative person CF of just what our game is doing we can either build a build cook and package and then run unreal insights against that or we can run against Standalone mode in both cases what we need to do is pass an additional argument as a command line parameter the structure of that command line argument I believe is Dash Trace equals default for what I was capturing before but you can also provide a comma separated list of arguments like CPU GPU for the individual tracks that we want to capture so I'm going to try Trace equals default and then I am going to switch this to Standalone game we're going to run that and with any luck we should see that session pop up and we do so right here I've got unreal insights running I also have the game coming up my game is now up I've lost my mouse Mouse but you can see as the game runs we are capturing a trace just like we did in the editor but now it is just my game running it is not any of the editor because we launched in Standalone mode so that is pretty cool when we close the game we will see the trace stop now let's look at a real world example I've been prototyping a game with time rewinding mechanics the way this works is each actor has a component it keeps track of its transforms and other state over time when I rewind time I simply play that state back in Reverse if you're interested in the full details I have a whole video on it but that's the gist of what's going on I also built a debug visualization feature that allows me to see all of that state unfortunately when I turn it on and a bunch of state has accured my frame rate absolutely tanks I'm really abusing the debug drawing API when I was looking at fixing this issue I was actually really surprised about why it's slow so it's a great example of why profiling is important to figure out what's going on I started by instrumenting my code I added bookmarks which again gives that little text visualization in the timeline view of unreal insights and by adding CPU profiler Scopes which will show up on my flame graph so I've got a bookmark for every time I turn my Snapshot visualization on and off which is that debug feature and I've also got a bookmark whenever I begin or end a rewind I've also gone through and instrumented all of the individual functions in my component so I can confirm that I understand why things are slow I was expecting the slowest part to be in debug draw snapshots because what we're doing is we're going through all of that state that we've captured we're calling draw debug point over and over and over every frame and draw debug line connecting all of those points over and over every frame here is what the profile actually looks like exactly as we expected the moment we turn on the debug visualization our frame rate tanks the density of the work that's happening in our flame graph goes way down and on our frame timings we can see that we go from running around 200 frames per second dropping all the way down to 10 frames per second if I select one of these frames and press F we can drill in and see what's going on the total time on the game thread is about 110 milliseconds interestingly most of that time is spent here in game thread weight for tasks about 90 milliseconds of that 110 milliseconds the rest of the time is being spent ticking our rewind components and calling debug draw snapshots which is what we expected to be slow some of these calls are up to 2 milliseconds for a single actor this would be completely unacceptable in a real game but the 14 milliseconds we spent ticking does not explain why is the frame 110 milliseconds long my original intuition was I'm going to come in to debug draw snapshots I'm going to you know Kick the Can down the road a little bit not really optimize this very hard use the lifetime properties on those apis to to make less calls every frame but this is a pretty good hint that that's not going to work and the reason that's not going to work is the way debug draw point and debug draw line actually work is they write down some State and that state actually gets consumed as part of rendering work and in fact if we scroll down and look at other fra other threads we can see that background worker number 14 in this case is where all that work is happening 94 milliseconds of that 1110 millisecond frame is happening on a background thread if I shift to the compact View and zoom out a little bit what we will see is there are these big blocks of work happening on very ious background threads and that's because the renderer is doing a bunch of background work that is moving around every single frame but this is really what the bottleneck is that is causing uh our frame rate to dip so hard unfortunately the details of what we are doing there is not instrumented my next step was to go into the engine source code add some instrumentation rebuild from Source repoint my project on top of that and this is probably overkill for the common case but I really wanted to cons confirm that I understood what was going on here here's what a similar profile looks like with that instrumentation added we can see that all the time is spent in draw debug Primitives and underneath that we are calling some functions in F batched elements uh so drawing points drawing thick lines in the code if we just scroll through there's a RDG event for adding debug Primitives that then calls into the element back Patcher uh there is a whole bunch of logic that is running here in F batched elements draw and this is where all of the actual work for debug drawing is happening so our current approach is totally doomed I had to do something completely different visualization V2 Grand reveal note we're running at a locked 120 frames per second when I turn the visualization on WE remain at a locked 120 frames per second the way I solved this performance problem is I moved off of the debug drawing pipeline entirely I made a new rewind visualization component that derives from the instanced static mesh component there's only one function here that is really important it's set instances from snapshots and I refactored my debug draw snapshots function on the rewind component to Simply turn around and call set instances from snapshot on the visualization component the way set instances from snapshots works is instead of running through all of of the state snapshots and directly calling debug drawing functions it instead runs through those snapshots samples them pulls out a bunch of transforms based on how much time has passed and how much movement has occurred since the last snapshot it then does a little bit of math to adjust the rotation of those transforms so that they look at one another it then updates all of the instance transforms on that instance static mesh component parent at this point all we're doing is using the standard unreal mesh drawing pipeline which is very good at drawing a lot of meshes and for the mesh I just used unreal's modeling tools to take a Taurus and an arrow and uh make a very super dumb simple mesh kind of looks like a Sonic ring but it makes me happy here's what the profile looks like with the new solution the main thing to notice is that our frame rate remains completely lock locked at 120 FPS we don't have a big degradation even when we turn on the timeline visualization you can see that's happening CU our bookmark is still here if I pick an arbitrary frame and drill in what we're going to see is that one that frame time is way way down uh total frame time now is on the order of about 9 milliseconds versus the 100 milliseconds that we saw before and the time we spent ticking also went way down previously we were ticking for about 13 milliseconds and some of our biggest offenders in the rewind component were taking 2 milliseconds each to tick now they're running between about 10 and 20 micros seconds on a fat one most of this is still in visualized timelines if I wanted to have an absolute ton of actors there are some pretty obvious things I could do to improve this further but for now our total time ticking for the entire frame for All actors in my world is less than a millisecond we have plenty of frame budget left and we are no longer spending 50 to 100 milliseconds on that debug draw Primitives RDG pass so this is solved as usual all my code will be up on GitHub feel free to do whatever you want with it that's all for today's Whirlwind tour of unreal insights if you found this useful you'd be doing me a solid by doing the standard YouTube engagement shenanigan slam that like button ring that Bell and if you want to learn more about my rewind project definitely check out that video until next time be kind to one another Peace

Channel: Nu Makes Games

Views: 22,018

Keywords: unreal engine 5 tutorial, unreal engine 5 games, ue5, unreal engine 5, unreal engine 5 tutorial for beginners, unreal engine, unreal insights, optimize games, frame targets, performance issues, fps, diagnose perf problems, profiling tool, game development, optimization, improve fps, fix unreal engine performance, unreal engine optimization tips, unreal engine performance optimization, How to Optimize Unreal Engine Games with Unreal Insights, game dev, Unreal Insights tutorial

Id: lfjG3z5VVIw

Length: 17min 40sec (1060 seconds)

Published: Sun Jan 28 2024