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Torvalds Explains Scheduler Decision
Firedog writes "There's been a lot of recent debate over why Linus Torvalds chose the new CFS process scheduler written by Ingo Molnar over the SD process scheduler written by Con Kolivas, ranging from discussing the quality of the code to favoritism and outright conspiracy theories. KernelTrap is now reporting Linus Torvalds' official stance as to why he chose the code that he did. 'People who think SD was "perfect" were simply ignoring reality,' Linus is quoted as saying. He goes on to explain that he selected the Completely Fair Scheduler because it had a maintainer who has proven himself willing and able to address problems as they are discovered. In the end, the relevance to normal Linux users is twofold: one is the question as to whether or not the Linux development model is working, and the other is the question as to whether the recently released 2.6.23 kernel will deliver an improved desktop experience."
Everyone except you.
Obligatory blog plug: http://www.caseybanner.ca/
Hasn't Linus already said he's very interested in adding it into the Linux kernel (going so far as to say that it could be a reason to consider going GPLv3 in the future if Sun releases Solaris under it), but right now it's tied up in closed source?
As it seems many others don't agree to his opinions of Con, http://lkml.org/lkml/2007/7/27/426
What do CFS and SD stand for in this case? The summary and linked articles do not describe this.
Having had my fair share disagreements with customers over technical issues, it just isn't worth trying to "win." The damage to your working relationships is still there even if you are shown to be 100% right. Try and help them address their problems as much as you possibly can, while trying to compromise as little as possible of the design. It's called diplomacy, and it's the difference between being given huge amounts of responsibility, and wanting to quit. You don't even have to agree with them, you just have to make them think you care.
Finally, it is common for programmers to try to avoid a subset of the problems in an area because it gives them the ability to write something "correct." Certainly a very satisfying experience for a programmer. However, that is exactly why it can be a bad idea to let a programmer rewrite a messy module. Very soon you can find the users of that module asking why a laundry list of things don't work anymore and an idealist developer trying to argue that they shouldn't... And it is exactly those idealists that like to rewrite working code. Not that major rewrites are bad, just that they have to be approached by someone mature enough to both expect a list of things they overlooked, and be willing to work with customers to resolve them.
-- http://thegirlorthecar.com funny dating game for guys
It's not closed source. It's available as part of OpenSolaris (CDDL). FreeBSD didn't have a problem integrating it.
Do you even lift?
These aren't the 'roids you're looking for.
Actually, I have no idea how an OS works and even _I_ know what this article is about.
I'm sorry but the flame wars over whether you call it zee eff ess vs. zed eff ess would make the vi vs. emacs flamewar look like a watergun fight. It would likely tear the Linux project apart as radical Zeddites suicide bomb the Zee Alliance.
The guy walked away. It's like quitting the Internet. Obviously if your reaction is to take your ball and go home (and I know, the ball is everybody's in this situation, but go with it) then you aren't mature enough to handle the responsibility Linus requires.
Slashdot - where whining about luck is the new way to make the world you want.
The real "Libtards" are the Libertarians!
Is CDDL compatible with GPLv2? I may have mispoke in my first post, but I think the gist of what I was trying to say is still there. ZFS is behind a license which isn't compatible with the license Linux is under. Or am I completely misunderstanding things? I'll admit I'm far from an expert on these matters...
Look at the front page much?
Do you even lift?
These aren't the 'roids you're looking for.
Number one can't be done some times. You may want Linux on the desktop, but at this point it is big on the server. It is used for a LOT of important stuff. If a scheduler makes games better but hurts general server performance, they just can't put that in without people eithe forking or switching. Now if it improved games and other desktop usage quite a bit but had a tiny effect on servers, that could be tennable. But if the effect wasn'nt tiny, they just couldn't blindly merge it.
All that said Linus makes a good argument. If the guy wasn't addressing problems well and was just arguing "that's not my scheduler's fault" or "prove that's a big problem" etc instead of working with people, there is a very good reason not to merge the code. Ingo wrote his quick and has spent lots of time with people since he did that working with others to find and fix problem workloads. He just seems to have been much more responsible about maintaining his scheduler and it's good performace.
There are trade-offs in evertying, and it sounds like Linus made a perfectly valid one here.
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
which kernel scheduler is pretty low on the list of factors affecting what the Linux desktop experience is all about...
frankly, really high quality experiences take organizational planning and leveraging the expereince of huge groups in way that the "bazzaar" model of software developemnt in open source does not do well. Would someone please just build a mutual benefit corporation for open source users and maintainers? Let's start paying for project managers and the other experienced professionals required to make a "desktop experience" and you will see Linux take over.
The official kernel site says 2.6.23 is only on release candidate 1.
Having lurked on http://www.lkml.org/ for several years, I find Linus to be rather rude. May be it's because English is not his first language...so words are not well chosen. I must say though, that I excuse him because he produces, [or helps produce] a very useful product on the world today. That is the Linux kernel.
I find Linus' comments very interesting, and very honest. He has good arguments, and to me it seems like he did the right thing. He is even open to change scheduler if someone can prove that SD does a better job than CFS, and get someone reliable to maintain it.
"If a scheduler makes games better but hurts general server performance..."
IIRC that is the reason Con together with another person, whose name I can't
can't be bothered to look up, wanted to merge plugsched to which they got a
reply along the lines of "too much choice will split contributors" or some such
And then Ingo turns around on himself, and claims something along the lines of
"Oh okay, you should work on plugsched, may be it'll get merged"
It's an interesting set of emails. In addition to admitting that he actually didn't have any problem with the SD code, Linus points out that he made a gut call that Con is difficult to deal with without even looking into it because, apparently on near religious grounds, he doesn't believe in reading "specialized" mailing lists. What i find of concern is that he'd express such strong opinions about people basically without having even spent an hour or two browsing some list archives. Further, he seems perfectly aware that he may have heard just one side of the story, and yet he STILL doesn't feel he needs to look into it further or to soften his view? WTF ?
... arbitrary ?
Has Linux kernel development always been this
From TFA (actually form the quoted emails) after several mails where Linus has been bashing this Con Kolivas guy for not taking feedback and being argumentative, and then offers some statements about the virtues of a good maintainer some guy "Kasper Sandberg" asks him:
"Okay, i wasn't going to ask, but i'll do it anyway, did you even read the
threads about SD?"
to which Linus responds:
"I don't _ever_ go on specialty mailing lists. I don't read -mm, and I
don't read the -fs mailing lists. I don't think they are interesting.
And I tried to explain why: people who concentrate on one thing tend to
become this self-selecting group that never looks at anything else, and
then rejects outside input from people who hadn't become part of the 'mind
meld'.
That's what I think I saw - I saw the reactions from where external people
were talking and cc'ing me.
And yes, it's quite possible that I also got a very one-sided picture of
it. I'm not disputing that.
"
You can be pretty damn right that the desktop experience is improved with Ingo Molnar's scheduler! If you have done any serious audio work on any platform you know that Linux kernel + Ingo Molnar's IO scheduler = the best platform for serious audio work. This combination has the lowest latencies. Linux kernel+Ingo Molnar's IO scheduler+Ardour offers currently lowest latencies and the best of all - it's completely free! It is pretty amazing - really. Every true professional audio engineer will agree with me.
That's not really fair. Slashdot pretty much covers all things science, be it computer science, or quantum physics. There are frequently articles posted which I, being in the field of computer science, do not necessarily understand or comprehend. I'm not going to tell all of the quantum physicists out there that "slashdot is not the place for them" because Slashdot IS for them. While it might have a technical slant to it, I think it's a place for anyone more interested in hearing news of advancements in various scientific fields, rather than what prison Paris Hilton is going to next.
For that matter, even when I don't understand what an article is talking about, I am still usually more than interested to read about it.
Whatever way you want to paint it, that's exactly what he did.
He believes that Ingo is a more reliable maintainer, so he chose Ingo's few-day old hack instead of Con's very mature and well tested scheduler.
Personally, I think that the person who is at fault here is Ingo, because he has a "Not Invented Here / By Me" mentality, and instead of developing Con's scheduler further, he totally objected to Con's work for ages (which prevented it from getting into mainline), and then suddenly saw the light and wrote his own quick hack based on the same design.
Ingo may be a good developer and maintainer, but he sure as hell isn't a friendly co-developer.
Why can't there be a flag that determines what scheduler is used at runtime, with both schedulers built into the kernel? I thought the whole point of Linux is that it is customizable and modular - I know this doesn't necessarily apply to the kernel, but why not?
;)
I know very little about operating systems, schedulers, and maintaining large projects, so please excuse any ignorance in my post
Come on, it's quite obvious that Linus's secret superhero alter-ego has done battle with Kolivas' supervillain identity before (I mean, Con Kolivas? Do the writers even try to make these things sound authentic?) and is now trying to thwart his evil plans of global domination.
... I find a bit of hypocrisy.
.... consideration about inclusion of code they wrote.. Uhhh did I forget to say its "Open Source"?
Three is right, as its Con and an email exchange between Linus and another.
Whooo hooo..
That settles it.... everybody is accounted for..... right??
Its open source but with all the talk about having a maintainer of certain character as a part of the consideration of
Its not uncommon for pioneers to be forgotten as what comes next, takes over...
Or does this mean that when a maintainer dies, so does what they were maintaining?
The general message Con seemed to be expressing was more interesting as a general observation than of specific code.
The response from Linus suggest that although Linus does not frequent specific topic lists because of inherent bias, he has his bias none the less.
There is a general across the board bias, proprietary and open source, and it is one of exclusion of the end users.
And it comes across as arrogance motivated by money and/or ego.
To explain, programming is an act that includes creating functionality that is then accessible thru an easier to use interface such as a function call with arguements and expected return value. The general concept is common knowledge in coding regardless of what programming language you are using,
However, this concept is not typically provided to the end user, but instead kept away from the user and certainly not provided to the user, when some distortion of it is provided the user, in any sort of easy common consistent manner.
To clarify, users access programs typically via a command line or GUI. Neither of which are so conducive to allowing teh users to put things together for themselves. All the functionality if available to the user via the programs GUI or command line. But the same functionality is not available in an mode that allows user to call the functionality in the program and make use of the results outside of teh programs command line or GUI interface.
Con mentioned the Amiga. The Amiga had all three user interfaces. The command Line, The GUI and the missing user interface an every other system today, The IPC port interface, most commonly known as the AREXX port but did not need AREXX running in order to use the port for "user putting things together for themselves".
SO YOU DON'T LET USER PUT THINGS TOGETHER FOR THEMSELVES! WHY NOT?
Cause you can dumb down the user and get ideas from them and sell those ideas implemented, back to them.
But when you take away from the users, the ability to put things together for themselves, then that makes you a hypocrite when you then call them ignorant, armchair coders or any other demeaning term. As it is you who have created that self supported dependency of trying to justify your lack of inclusion of others.
Con outright stated how he got started.
Maybe You linus and a whole world of other coders, need to pull you head out of your asses and SERIOUSLY realize, THERE ARE OTHERS you are not considering.
Ultimately, if people want to optimize their system for their needs, they should be able to. But there is serious prevention of that across the board.
Have you improved it to the point that when the system is borderline out of main memory or has a moderately high load average it actually *works* as a desktop system?
E.g. when Firefox is consuming 65-70% of main memory and slower than #%#$ and you know it is waiting on swapped out pages and your swap rate is measured in the dozens to hundreds rather than hundreds to thousands (on vmstat)? (I mean really, how can one take an operating system seriously when only memory is at 100% and not CPU + memory + Disk I/O?)
The real issue, for those who have read comments that Con has made in interviews, seems to be the lack of concern on the part of most of the "in-crowd" Linux developers for performance on the desktop. In part this seems driven by the fact that the people who actually get paid to maintain Linux, benchmark it and "improve" it only care about its performance in server farms and *not* on the individual desktop. I will weigh in on the side of desktop user out there (that wants the Linux sitting beneath their desk to devote its every waking minute to making *them* happy) by saying that if my mplayer "hangs" in the middle of a song (only to continue with a loud burst of noise 10 seconds later) when the CPU is busy with "nice -19" processes, my Firefox browser takes half a minute to scroll a page or open a screen) when memory is tight, and it takes minutes to bring up a tab or minimized program I haven't touched in 3 days and return them to a functional state then the operating system *Has a PROBLEM*.
Con was very clear in his interviews that the problem is the lack of caring about *desktop* performance. Given my comments in the previous paragraph -- some of these areas may be very difficult to benchmark and as a result one is left with nothing but handwaving and loud voices when it comes to discussions about whether the problem exists and how it should be fixed.
I will say this, in the mid-'90s I used X-windows under Unixware on *Pentium 1s* as a desktop machine. I now use X-windows under Linux on a Pentium 4 (with 5-10x more main memory) as a desktop machine. I would argue that my desktop user experience is as problematic now as it was then *despite* the hardware improvements. That IMO is what Con felt was the problem he was trying to address. That is what it would appear the core Linux developers may be failing to address. Con's points raised my awareness level to the extent that I actually went investigating to see whether there were open source distributions of the BeOS and/or Darwin (which is based on Mach) available since they are based on different OS architecture models and might be more end-user friendly [1]. I was hoping to find something I could run in a VM under Linux on my current hardware without major file system surgery. But I have little confidence that such an approach would fix core problems with the Linux scheduling and paging systems. I would *love* to see a real side-by-side comparison of Linux vs. FreeBSD for desktop users with an emphasis on how BSD scheduling, paging and swapping may be different (better?).
(And as a side note, I could care *zero* about the performance of Linux in file server applications!)
1. I did use both Nextstep (on Pentiums) and IRIX (on a R4000) for a while and found both to provide better end-user experience than Unixware (X) or Windows (95-98). I am disappointed that Linux barely manages to match those experiences given the hardware available nearly a decade later.
1. Games run just perfectly on Linux with often better speed than in Windows. Every single game i has played in Linux has worked perfectly and smoothly. What Linux needs for gaming is more normal users who buys games. If there is a market someone will fill it quickly. I will also strongly refute that games are essential to desktops. There are infact people who use their computer to actually do something useful. 2. This decision has nothing to do with egos. This guy just happens to believe that its essential to speed up the kernel when the only slow apps in Linux are non-native apps like Java, OpenOffice or Firefox. Those are not slow because of any sheduler but because they are written with slow toolchains. More work on making the kernel more responsive wont help at all at this stage.
HTTP/1.1 400
[emphasis mine]
I'm gonna have to go with Linus on this one.
That's not true. Non-GPLed kernel modules are "tolerated" by the Linux kernel developers, and in principle, a ZFS module could be created and loaded with no problems, assuming it doesn't rely on GPL-only symbols. AFAIK, the VFS doesn't have many of those.
What can't happen under the CDDL is the ZFS code being included in the kernel source tree the same way XFS, ext3 and so on are. That doesn't mean you can't maintain and distribute a module separately! The only reason a ZFS module doesn't exist today is that nobody's gone through the trouble of creating one.
Whether Con was aware of it, when he tried to integrate into mainline Ingo was his main customer. Specifically the person he was trying to deliver work to. And Con committed the cardinal sin of telling a customer that the customer was wrong about what he wanted. Even if Ingo were too coked up to operate a keyboard reliably and had it all wrong, trying that never seems to work.
Did Con gain anything by refusing to re-introduce the hack to get X working the way it had previously under load? Even if he'd just put in a #define that allowed it, and then spent the next year arguing to take it out, there wouldn't have been this breakdown.
-- http://thegirlorthecar.com funny dating game for guys
Start profiling the damn thing! Write performance tests, good ones, write really evil stress tests, stress the crap out of it, and then you will know what is *wrong*. Might not be the kernel at all, in fact, I think that a lot will be because of applications (always a huge source for problems), the UI/Graphics subsystem (again, huge source for trouble, X11, drivers, UI toolkits, they all tend to be far from perfect) and such.
:(
But pissing and moaning won't do you any good. At least Con did try to write stuff, but not being a professional software engineer hurt his efforts I'm assuming. The guy would probably make a good technical manager though. It is a shame he felt he had to quit, it would have been much better if he could have gotten a few other kernel hackers on with him to go on. I think he ended up with a lot of users backing him, but no coders
Not that I am a Linux person, but I always find it sad to see people who are really into something quitting for bad reasons (bad in the sense that the shouldn't have to, not that he did something unwise).
The situation for Linux is even simpler, since hardly anyone actually uses the stock kernel. Most Linux users use a kernel supplied by a distribution, which is compiled with a specific set of options and typically a few hundred patches. If one scheduler is good for desktops, and one good for servers, then merge them both and let desktop-focussed distros pick one and server-focussed ones pick the other.
I am TheRaven on Soylent News
More like Surf's Up, but with emphasis on kernel development, instead of surfing. By the way, stay tuned for Dreamworks' Pictures "Tux". An animated comedy, starring yet even more penguins, and the lovable little guy himself. Tux is an ordinary penguin, working away at his operating system all day, like good penguins should. A chance meeting with the BSD Daemon and Gnu marks the start of a grand adventure that takes Tux all over the internet (including a brief visit to Slashdot itself). Tux makes friends with a host of colourful characters, meets the girl of his dreams, and learns an important lesson in process prioritization and task scheduling.
Unlike porn, which yada yada rimshot hey-ooh!
And what's with the massive ego? It's as if suddenly Linus thinks he invented compilers or something. I think he needs to take a vacation and regain some perspective.
This post expresses my opinion, not that of my employer. And yes, IAAL.
The CDDL was designed to be GPL incompatible, Solaris didn't want its crown jewels to be in Linux.
Furtunately, you're offering just an uninformed (and trivial at that) opinion. Unfortunately, you opinion seems to resonate with a large segment of similarly narrow-minded slashdot users. It is particularly tragic when folks here gravitate toward one steep world view without any desire to explore anything else outside of their comfort zone. It is a good thing that vocal narrow-minded elitist views (irritating as they are) are easy to ignore. The fact that diverse stories make it onto slashdot for all to discuss speaks volumes about that kind of site Slashdot actually is. We choose which stories we wish to participate in. The reality is that no one person (or even groups of persons) gets to define what slashdot is or isn't. Instead of helping to insulting others for not knowing much about the inner workings of the kernel, wouldn't it be more instructive to educate them on a subject which you (presumably) are more knowledgeble of? Instead of pushing your own agenda on a public community, why not take the time to look around and listen to what others may have to offer and then make the effort to make *your* contribution to other who need it? Please understand, I am not trying to attack you personally. I'm sure you're a decent upstanding guy. But the perspective of the opinion you've just expressed comes from a direction that hails from the most unsavory part of this great community, one that insults inteligent people and gives us all a bad name.
Stay sentient. Don't drink bad milk.
Or having a cat who fubared your keyboard, so you're typing posts via ascii codes.
Your ad here. Ask me how!
over MS ones any day.
Sounds to me either scheduler will do the job just fine.
The decision between two good alternatives is always a difficult decision - someone, no matter how good the ideas, will feel slighted.
A few months before Ingo wrote the O(1) scheduler, he flamed anyone who dared to suggest that an O(n) scheduler is a bad idea. He was *very* aggressive about it, going on and on about why O(n) is best and how O(1) would be worthless. Using Linus's words (about Con), Ingo "ended up arguing against people who reported problems [scheduler linearity], rather than trying to work with them". It therefore seems a bit strange that Linus uses this statement to describe Con, arguing this is why he favors Ingo...
Importantly, Ingo was dead wrong back then (indeed, this is why months after, Ingo came up with the O(1), announcing it as if it was his idea and as if nothing ever happened, not *ever* saying something like "I was wrong, sorry for the flames").
In contrast, Con was right in refusing to pollute the design of SD with Ingo's unfairness discipline. (This is what Linus referred to when he made the "arguing against" statement.) And what do you know? A few years after, Ingo comes up with a "Completely Fair Scheduler"...
I'm in scheduling research for many years. I followed the long Linux scheduling saga, which actually started way before Con was in business. Please believe when I tell you: Linus comments about Con are ludicrous, and petty. This is not Linus's finest hour.
Note however that this does not mean that Linus made the wrong decision: Even though SD is somewhat better than CFS, Ingo is orders of magnitude a better programmer than Con, orders of magnitude more knowledgeable, he gets paid to do the work, has gotten along with Linus for years, and will eventually make CFS as good as SD and even better. This is the real reason for Linus's decision. (Or at least, it should be.)
But the stuff Linus said about Con... well, that's just Linus being small.
Ehmm... I'm not a 'gamer'.. Maybe once every 2 months or so if i don't have anything better to do... But most people i know below 30 are playing games, and without having good support for that in gnu/linux they will never switch away from windows.
The problem the linux distributions have today is that they have a bad reputation that scares people away and this scares people away from it.. (remember that all unknowns are scary for most people)
Now back to the topic... First of all i do want to say that i have not had the chance to try the CFS scheduler yet, but the thing here is that the SD scheduler where great on lots of other tasks too. With the plain O1 scheduler i had lots of problems when playing video-streams during high-cpu load,and the issue was that the scheduler gave background-jobs to large timeslices that cause the player to skip frames and such. With the SD scheduler there where some really nice things you could do then too, like setting the background-jobs to SCHED_ISO that caused the process ONLY to use unused cpu-time and this worked great. Could have 5-6 gcc's loading the cpu without even a frame dropped and did try out a opengl game (enemyterritory) during compilations just to see how it worked, and no problems there either.. Then after switching back to the O1 scheduler i could not even have 2-3 gcc's running without loosing LOTS of frames, and did not even bother with trying out a game..
So you see, games are just a part of it.. All types of lowlatency applications like video, music, games and some daemons like nfsd and such needs a good scheduler to give the best performance/interactivity.
I think i'm gonna give the CFS scheduler a try during the week, but i dont have any high hopes after what people have reported about it yet. And i do think it would be a better idea to implement multiple schedulers that you could choose between instead of having 'one size fits all'.
A few months before Ingo wrote the O(1) scheduler, he flamed anyone who dared to suggest that an O(n) scheduler is a bad idea. He was *very* aggressive about it, going on and on about why O(n) is best and how O(1) would be worthless. Using Linus's words (about Con), Ingo "ended up arguing against people who reported problems [scheduler linearity], rather than trying to work with them". It therefore seems a bit strange that Linus uses this statement to describe Con, arguing this is why he favors Ingo...
Importantly, Ingo was dead wrong back then (indeed, this is why months after, Ingo came up with the O(1), announcing it as if it was his idea and as if nothing ever happened, not *ever* saying something like "I was wrong, sorry for the flames").
In contrast, Con was right in refusing to pollute the design of SD with Ingo's unfairness discipline. (This is what Linus referred to when he made the "arguing against" statement.) And what do you know? A few years after, Ingo comes up with a "Completely Fair Scheduler"...
I'm in scheduling research for many years. I followed the long Linux scheduling saga, which actually started way before Con was in business. Please believe when I tell you: Linus comments about Con are ludicrous, and petty. This is not Linus's finest hour.
Note however that this does not mean that Linus made the wrong decision: Even though SD is somewhat better than CFS, Ingo is orders of magnitude a better programmer than Con, orders of magnitude more knowledgeable, he gets paid to do the work, has gotten along with Linus for years, and will eventually make CFS as good as SD and even better. This is the real reason for Linus's decision. (Or at least, it should be.)
But the stuff Linus said about Con... well, that's just Linus being small.
Don't worry, there are enough non-knowledgeable people here to mod you down. I must admit that this debate really boils down to Linus and Ingo taking a long time to reach Con's conclusions, and then not being as gracious about it as they could be. Con, of course, was insulted by this (who wouldn't be?) and all the while we had two major camps of Linux users: the pro-CK one (holy crap! My system works with this patchset!) and the anti-CK one (damn! My server doesn't need this, wtf?).
In the end this just demonstrates that having egotistical bastards running the show isn't always going to yield the best results. Linus and Ingo do fantastic work, and they do sub-par work. But when someone points the sub-par stuff out, head for the hills! They will always have a legion of fans defending them, more than willing to dumb-down the real issue in favor of pretending their infallible leaders are never wrong.
So, lets says you're running Word (not likely on linux, for quickest example I could come up with)
What the fuck.
After all, I am strangely colored.
This whole situation reminds me a lot of devfs. The developer of devfs (Richard Gooch) was maybe a bit of an outsider with good ideas and strong opinions that sometimes clashed with those of kernel developers that were more insiders or closer to Linus. The story is a little different in that devfs had actually made it into the mainline kernel, but then later was replaced by udev (the first draft of which was by Greg KH in a day or so... again very much like Ingo's whipping up the first draft of CFS).
/lot/ of energy into their work. But that energy was not lost to the rest of us, as without the experience of their groundbreaking we would not have gotten the solutions we eventually did. Even if Greg KH's udev and Ingo's CFS share no appreciable amount of code or algorithms with devfs and SD, if they are honorable, I'm sure they would admit that they could not have so quickly whipped up their solutions without the example and inspiration of RG and CK's work.
/Maybe/ instead of losing them in the long run we could have gotten some more innovation from talented developers like RG and CK. The problem, I think, wasn't the decision adopt CFS instead of SD. Rather, regardless of whether or not is true, the problem is Linus's public judgement that CK is not a "responsive maintainer". I didn't follow the CK or the lkml lists in that time frame enough to know if he is right... but a really good leader would not have made such a judgement public even if hed believed it, and instead would have worked to find a way to keep such talented persons contributing.
Then as now with CK, eventually Richard stopped doing linux kernel work altogether. I thought it was a sad loss of a talented kernel hacker, and I had been a devfs user, but I must say that in retrospect I do think udev is a better solution. It is simpler, has less impact on the rest of the kernel, but has proven itself to solve all the problems devfs tried to solve that actually mattered.
What's the moral of the story? That both sides are right... on the one hand, there's something sad here, because at least several times in linux history an outsider had to fight for innovation and in the end was pushed away even as his innovation was grudgingly adopted by reinventing it. On the other hand the actual results do seem to indicate that linux is NOT resistant to change, and maybe that the better, more maintainable solution tends to win out.
There's also another thing to keep in mind... it is a pattern in this history of technology that the first attempt to solve a problem is rarely the one that becomes dominant. Both Con Kolivas and Richard Gooch should be recognized for the innovators that they are... and if they were wise they should also not begrudge the fact that it wasn't their exact solution which eventually got adopted by the mainstream. I know this is difficult... they both put a
Finally, I would like to add that although the way I see all this, it has little if anything to do with Linus's personality, nevertheless I think Linus could have handled these cases better.
Somebody directing a large effort does not have the ability to fully investigate every subsidiary dispute fairly without the effort grinding to a halt. Shorthand criteria are a necessity, as are rules of thumb as to what sources to bother investigating. This will inevitably lead to a number of less-than-optimum technical decisions along the way, but the results will be markedly superior to those where the manager stops everything to thoroughly investigate every aspect of every decision.
Con Kolivas's reaction to "losing" was not to continue to maintain SD and try to get it in later, or to try to improve CFS, but to quit kernel-hacking entirely. Which means he is not of a temperament that can accept that large projects will have arbitrary decisions that go against him, which means he would be a bad choice for the maintainer of a major kernel system. His actions in retrospect justify Torvalds's judgment that he couldn't trust him as a maintainer. Kolivas proved Torvalds correct on the management question, even if Torvalds is wrong on the technical one.
It would be perfectly possible to have ten different schedulers and just choose at compile time. The question is, is it really worth it? The performance benefits are pretty small compared to if you have better optimized code in the games or better drivers for the graphics card. A better scheduler doesnt solve buggy drivers, bad coding or bad ports. If i understand Linux correctly he is more than fine with people using whatever sheduler they want in their own trees. Hes just not that hot for maintaning more than one in the vanilla tree because its not just worth it. Again, there are much bigger improvements to get in other places that people tend to completely forget.
HTTP/1.1 400
I fully agree with the first part of your post, but I don't buy this 'Con's reaction justify Linus judgment' argument:
1) It seems clear on the mailing lists that Con was really a good maintainer (only one 'problem' reported).
2) Con's reaction seems quite understandable, after a very long time working on a project you see it not only refused by the maintainers (perfecty ok on that), but suddenly 'copied/inspired/wahtereryouwant' by that very same maintainer (not quite right).
EGO leads to sectarism, that's all. The problem is that it seems that Con's scheduler was very good at gamming, and it's a shame that Linux dimissed a good piece of code on a specially sensible area for personal motives.
What's in a sig?
I don't disagree that a story about the scheduler is potentially interesting, and that it's what Slashdot used to be about. But as you can see from the above comments, it's not exactly stuff that "nerds" these days care to Google when they don't understand what it's about. Personally, I started reading this site because I ran (and run) Linux, not the other way around. So I've got nothing against this particular story, even though most of the discussion is very poor, and, sadly, typical for this site.
That said, I do disagree that Slashdot has ever been a science site. There's a lot more to science than what interests the nerd crowds (the proper nerd crowds, not the Apple fanboys and gadget freaks, who could care less about how stuff works). Science, as it concerns Slashdot, is mainly science that concerns technology. Throw in a few dinosaurs and volcanoes for good measure. It's boys' stuff. Science fiction stuff. You won't find anything about the travel patterns of herring or anything that takes the social sciences seriously (plenty of people here would even claim "it's not science", demonstrating their own lack of insight into what the scientific method(s) constitute).
My read is different, but it'll take a few paragraphs to explain why, so please bare with me. The O(1) so called "improved interactivity" was just a hack upon a hack upon a hack that never worked. If you ever read the code you know what I'm talking about. It was a complete mess. The mess was the result of trying to obtain a goal that is unobtainable: very roughly speaking, Ingo (and others) believed that it is possible to deduce how "important" a process is, based on the frequency of the process' sleep events (not the duration of the sleep). I can point you to a few research papers that show that this can simply *not* be done. Briefly, it has been shown that for each "important" application you can find an "unimportant" application such that the CPU usage pattern of the two is very similar; Hence, you would never be able to distinguish the important from the unimportant (if you are only basing you decision on CPU usage). All you can do is (1) divide the CPU equally, and (2) provide good response time to applications that sleep for long periods of time (like editors). According to several of his emails, Ingo is not reading scheduling papers, and proud of it.
I suspect Con doesn't read such papers either. But he knew this is the case nevertheless. For years Ingo and his followers attacked Con on this. Note that this is a purely technical issue, and Con was *completely* right, e.g. take a look at CFS, or at Linus's original scheduler that lasted until 2.2, or, Solaris, *BSD (with the exception of ULE), HPUX, etc. They are all much closer to the SD's philosophy than to the O(1)'s. (BTW, the only other OS that tried to do what Ingo wanted is... the Windows family).
The discussion between Con and others regarding this issue was not about minor details. Ingo and his followers view towards Con was plain and simple: "your design is crap, it doesn't do what schedulers are supposed to do". Con resisted. And I agree, after years in the business, he was occasionally emotional about it. But this is really understandable and reasonable. Especially when you compare it to the way Ingo and Linus express themselves from time to time (talk about "drama queens"). For example, notice how Linus talks to Ingo when Ingo doesn't understand something immediately.
The bottom line is that most of them are "drama queens" from time to time. Nobody is perfect. In absolute terms, however, I think Con usually expresses himself in a calm, quiet, and relatively humble manner. Certainly in comparison to Ingo/Linus.
>Even though SD is somewhat better than CFS
Ah ok a solution is better... We use that solution, right? Because after all is that not what Open Source is all about? (http://en.wikipedia.org/wiki/Meritocracy)
Meritocracy is a system of government or other organization based on demonstrated ability (merit) and talent rather than by wealth (plutocracy), family connections (nepotism), class privilege, cronyism, popularity (as in democracy) or other historical determinants of social position and political power.
>Ingo is orders of magnitude a better programmer than Con, orders of magnitude more knowledgeable, he gets paid to do the work, has gotten along with Linus for years, and will eventually make CFS as good as SD and even better.
Ok so demonstrated was a scheduler that was better, but chosen was somebody who is perceived as being more knowledgeable, and gets along with Linus and EVENTUALLY will make CFS as good or better... And until EVENTUALLY hits I should wait around and suffer the problems? And how is this different from say Microsoft who refuses to fix bugs?
Let's call this what it is! Corporatism at the open source level with Linus's nepotism!
"You can't make a race horse of a pig"
"No," said Samuel, "but you can make very fast pig"
I'm only 19, and I've never contributed a single patch to any software project, but even I know exactly what this is about. The worry here is that the Linux kernel developers are acting like snobby elitists, and that they care more about patting each other on the back than they care about improving the kernel. They're rather shit up the kernel than listen to someone who isn't part of their inner circle. It's pretty major stuff.