The Completely Fair Scheduler's Impact On Games

eldavojohn writes "We've heard a bit about the completely fair scheduler previously, but now Kernel Trap looks at the implications this new scheduler has for 3D games in Linux. Linus Torvalds noted, 'I don't think any scheduler is perfect, and almost all of the time, the RightAnswer(tm) ends up being not one or the other, but somewhere in between. But at the same time, no technical decision is ever written in stone. It's all a balancing act. I've replaced the scheduler before, I'm 100% sure we'll replace it again. Schedulers are actually not at all that important in the end: they are a very very small detail in the kernel.' The posts that follow the brief article, reveal that Linus seems quite confident that he made the right choice in his decision to merge CFS with the Linux kernel. One thing's for certain, gaming on Linux can't suffer any more setbacks or it may be many years before we see FOSS games rival the commercial world."

Comments

Article is misleading

[RailGunner]

Funny, in the article those framerates for Quake III show CFS beating the pants off of SD.

Besides, the biggest barrier to 3d games in Linux is video card drivers (ATI, I'm looking at you!) as 3D drivers in Linux, even the proprietary ones, have tended to be unstable.

Linus is right one this one, the scheduler is a small part.

Re:Article is misleading

[Aladrin]

Yeah, I was just gonna post 'Long story short: CFS is better. -yawn-'

Why not just say that, instead of trying to get a bunch of ./ers to RTFA?

Re:Article is misleading

[complexmath]

The performance of the "patched SD" mentioned near the bottom show SD to be slightly better than CFS on the test system. However, a few FPS one way or the another really amounts to testing "noise" -- it doesn't mean anything. If there are any problems with 3D, it obviously isn't common to all systems, which suggests to me that the scheduler isn't the problem. Not unless the problem systems have some background job running that the others don't, which is messing up CFS in some way (and this seems unlikely).

Re:Article is misleading

[Omnifarious]

FPS is a poor measure of the feel of a game. I know it's what all the graphics card benchmarks use, and it does do a good job of measuring the total processor and video card throughput, but that's not the most important thing.

The most important thing is the time between you pressing a key and the changed game state being reflected on your screen and how consistent that delay is.

One of the arguments that CK has made about kernel development is that kernel developers have become obsessed with throughput to the exclusion of all else and that this leads to very poor desktop performance because throughput is a poor measure of 'interactivity'. Someone posting 3D game framerates as evidence of one scheduler being better than another is exhibiting exactly this bias.

IMHO latency is a better measure, but still not perfect and it can be hard to measure in some cases.

I don't know enough about the scheduler to know which one is better or which one exhibits particular properties. But I can see that the throughput bias is evidenced in force in the thread the article points to.

And CK is also right that big iron shops care more about overall throughput than any measure of 'interactivity'. IMHO there ought to be some kind of pluggable scheduler system that allows you to completely change the algorithm to reflect the preferred behavior of the computer you're using.

Re:Article is misleading

[sumdumass]

I believe that you can swap the scheduler out. I might require you to rebuild the kernel but there is nothing stopping a distro, you or anyone else from using a different scheduler.

And actually, If people think this is a problem, Distro's already heavily customize the kernels so switching this out in their particular kernel shouldn't be much of a problem.

Re:Article is misleading

[Bob-taro]

FPS is a poor measure of the feel of a game. I know it's what all the graphics card benchmarks use, and it does do a good job of measuring the total processor and video card throughput, but that's not the most important thing. I disagree. Responsiveness is important, but I've never encountered a situation where the frame rate was good and the machine couldn't read my keyboard clicks fast enough.

You won't get good games until you get marketshare

[nweaver]

This is irrelevant to the gaming front.

The limit to games on Linux is market share. Its not (much) easier to develop a good 3D game for linux as it is Windows, so why code for 2% of the market when you can code for 92% of the market?

Thus you will only get games where the developer has gone out of their way to ensure complete portibility and provides a port mostly out of courtousy.

The scheduler details are irrelevant for this: what Linux Games need is 10%+ marketshare on the desktop.

Re:You won't get good games until you get marketsh

[Zironic]

Sounds like an evil circle.

To get Market Share you need games.
To get Games you need Market Share.

Pluggable

[cerelib]

That is why Linus should have listened to Con Kolivas when he tried to introduce a pluggable scheduler system. With a modular system we could have CFS and the staircase scheduler and both problems solved.

Setbacks?

[ichigo 2.0]

One thing's for certain, gaming on Linux can't suffer any more setbacks or it may be many years before we see FOSS games rival the commercial world.

Linus mentioned somewhere that CFS and SD are both superior to the old scheduler, so in what way can choosing CFS be considered a setback?

Linux and Games

[CopaceticOpus]

I've figured out how to get games running with Linux!

1. Set up your Linux system. Use onboard video and don't overspend on your processor.
2. Buy a PS2, a Wii, or a 360.
3. Play games on your game console and do everything else on Linux.

Be glad they chose CFS over SD then.

[delire]

Sayeth Kenneth.

Alright, Just got done with some testing of UT2004 between 2.6.23-rc1 CFS and 2.6.22-ck1 SD. This series of tests was run by spawning in a map while not moving at all and always facing the same direction, while slowing increasing the number of loops.

CFS generally seemed a lot smoother as the load increased, while SD broke down to a highly unstable fps count that fluctuated massively around the third loop. Seems like I will stick to CFS for gaming now.

--
Kenneth Prugh

Sayeth Matthew

My experience was quite similar. I noticed after launching the second loop that the FPS stuck down to 15 for about 20 seconds, then climbed back up to 48. After that it went rapidly downhill. This is similar to other benchmarks I've done of SD versus CFS in the past. At a "normal" load they're fairly similar but SD breaks down under pressure.

The only other thing of interest is that the -ck kernel had the WM menus appear in about 3 seconds rather than 5-8 under the other two.

The only chap that says otherwise doesn't post his results.

From TFA

Re:FOSS games

[sqlrob]

It depends on the artist.

Are you saying all of "Snow White" was drawn by one person? All 24 fps, 83 minutes worth?

Re:Strange, I've been gaming in Linux for years.

[Stephan Seidt]

Performance improvements could come from i.e. unsupported and thus unvirtualized eye-candy DirectX features which would have a negative impact on performance under normal circumstances. Anyway, afaik all the mentioned games have OpenGL renderers, but I assume that you use the stanard DirectX renderer in World of Warcraft.

On the other hand, performance drawbacks because of wine's virtualization are very small but naturally they do exist. Adding an extra layer of wrapping takes time. Of course, maybe wine's handling of win32-specific calls and systems is more efficient than Microsoft's implementation in their operating systems ;-)

Re:FOSS games

[Catil]

Artists usually have a huge archive of unused material, either done in their free time for practice and fun or for games that never used it due to a redesign or cancelation. Even some of the dummy objects most artists produce, to give the coders something to work with, can be better than actual graphics made by a hobbyist.
I always wondered why they just wouldn't contribute at least some early works to the open source community? Is it maybe just the lack of a good website where stuff like this could be indexed or isn't there a good enough standard license model to release something like that for free? I thought the Creatice Commons license would be quite suitabel for it.

Everybody who spent some time finding a good textured and rigged low-poly character model, preferably with basic animations, on the net for use in an open source game, knows that there is next to nothing available. Well, at least not when I could have needed one about two years ago.
It really doesn't have to be that professional or finished - even that untextured rat someone made a decade ago to have something to shoot at, later to replaced by some creatures, could maybe be of use to someone; and if he textures it, and maybe do a simple animation and perhaps record some sounds, and then uses it in his project, he should give the additional stuff he made to other developers as well.
Soon there will be a nice looking 3D rat with some textures to choose from, various sounds, walking and death animations, etc. and everybody did his part. That's the open source way - why does it seem it's not very common among artits and only coders?

Anyway, I think it could be really just the right website that is missing - some Sourceforge-style page with a nice upload-frontend, where stuff gets properly indexed based on categories, tags and styles and with a feedback option, where contributers can see which projects are using their works. Add some voting to rank it, karma, apply a fair license to it upon upload and I think something like this could really take off.