What You Should Know About Load Times

(cleverly abbreviated as WYSKALT)

If I have time to get pissed off and say "I can't help but notice that I'm not playing your game RIGHT NOW," then it means your load times suck and I'm probably wondering why I bought your game in the first place.

This seems bad!

Loading your game off media isn't rocket science. I'm going to assume that we're loading off some kind of disc with a 'c' media like in a console game rather than your hard drive like on your PC of choice. However, anything applied to optimize load times on disc-with-a-c will also optimize disk-as-in-hard-drive as well. I'm not going to cover everything with load times in this post, but this is the absolute bare minimum of stuff you need to know but I couldn't fit it in quite as catchy an acronym. There's lots more stuff that will make load times even better which I might rant about at a later date.

So at any rate, here we go.

Opening Files Sucks
Most times we don't notice this. Occasionally you run into something where you need to load N files which are kinda small but where N is something gigantic (like 1000). Then you notice--even if you have an uber fast machine. On this generation of console, N is usually on the order of thousands for a given level load for those who might be curious.

Fixing this is uber-easy: pack all your files into one giant uber-file so you only ever need to have one or at most a small number of file handles open. We often know of these as zips, wads, paks, pigs, etc. (The one I use for BEER is "keg". Clever, no?)

This makes load times suck less which is the goal. Sadly, they still suck.

Loading Non-Sequential Data Sucks
So now you've got your data all archived and it's time to load it. Surprise! It still takes a long time because you're constantly seeking around in your uber file. I can hear you smug Win32 people scoffing--but remember that your file mapping eats virtual address space and I know that since you're still using WinXP that you only get two gigs of VM. Ha!

This is pretty easy conceptually: stick all the data in your archive in order. The bad news is that depending on your particular data set and load time trickery, this might be really hard in practice. Chances are good that it leans toward the really hard side because you might only load some subset of your data and probably don't have a fixed order for it. If you can make your loading respect a fixed order then the problem moves pretty quickly to the easy side again.

I've found that in most cases the best we can hope for is that some subset can be made to lean toward "most" for fixed sequentiality. Sometimes you can change the loading code to do nicer things; sometimes you can't for <fill in the blank> reason that fits your situation. In either case you need to generate a sequence list for some set of your data then stick all the data in your archive in that order as best you can. Neither of these are particularly difficult assuming you have source code and enough time to do stuff and an archive builder that doesn't totally blow chunks.

Why does this work? Once file open issues are dealt with, seek time tends to be the dominant factor in unruly data sets. On discs-with-a-c, each seek is going to weigh in at roughly between 50 and 150 milliseconds depending on your particular hardware. So, if you're loading 10MB of data but seeking 100 times, your load bandwidth for that data can be no better than 1MB/s in the best case (assuming a flat 100ms/seek which is normal). If you try to load a gig of data with that bandwidth, then, well, I'll not be alone in returning your game.

So: if you can significantly reduce the number of seeks your game needs to do, you can significantly reduce the load time of your game. I've seen particularly poorly loading data sets extend the load time of a 100MB data set more than five minutes. For those in the audience reaching for calculators, that's a bandwidth of less than 1MB/3seconds. Glacial.

But Our Game Is On the Hard Drive!
Don't care. These will still make your loads better. Your seeks are still on the order of 8ms and your bandwidth isn't free. Wait till your users start fragmenting the crap out out their drives. Galactic Civilizations is a reasonably fun game but its load times are absolutely brutal. Why? Tons of tiny files none of which seem to be in easy-to-load formats just sittin' there on the disk. Lots of games are like this for the PC and it's a damned shame.

Oh! You did that for your modders, did you? Guess what; you can still put most of your stuff in order in archive. You can even give modders your packing tools so their stuff loads fast too! Sure, you have to design for it but you're already designing extra stuff in for modders, right?

Odds, Ends, and Disclaimers
As mentioned atop, this is the bare minimum you need to know about load times. There are lots of other things you can optimize to make your loads suck less but I'll save that for another rant.

This has been a public service announcement paid for in part by the "Your Game Loads Too Slowly" foundation of Maryland and made possible by viewers like you!